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Overview
PhotoGIFｪ is the most powerful tool available for creating optimized GIF and GIF animation files for the web. It uses advanced color reduction and compression technology combined with powerful features not found elsewhere to make producing GIF and GIF animation files easy and efficient.
PhotoGIFｪ is an Adobe Photoshop 3.0 File-Format plug-in that integrates seamlessly into Adobe Photoshop. It combines open-and-save simplicity with the most powerful features available for creating GIF and multiple image GIF animation files.
What is GIF?
ﾔGIFﾕ stands for the ﾔGraphics Interchange Formatﾕ and was developed in 1987 by CompuServe, Inc. to provide a simple, efficient format for the presentation of graphics over the CompuServe on-line service. Because the needs of CompuServe, Inc., when developing the GIF format, closely matched the needs presented by the web, GIF was adopted as the in-line graphic file format for early web browsers. It has since become the primary graphics file format for the web and is supported by all graphical browsers now.
GIF is an ﾔindexed colorﾕ format, which uses a palette limited to 256 colors or less. RGB data is stored only in the palette of GIF files, and pixel colors in a GIF image are referenced to the RGB values stored in the palette with one byte indexes into the palette. This means an uncompressed indexed image will be exactly a third as big as an uncompressed RGB image.
In addition to the reduction in image size by the indexed image, GIF is a compressed format and uses ﾔlosslessﾕ LZW compression to further reduce the size of the image data in the GIF file.
There are two versions of the GIF format, GIF87a and GIF89a. GIF87a files are based on the original file format specification, while GIF89a files are based on a later revision of the specification which added transparency and multi-image capability to the GIF format. GIF89a is backwards compatible with applications only supporting GIF87a files.
Installing PhotoGIFｪ
To install PhotoGIFｪ simply place the ﾔPhotoGIFｪﾕ plug-in inside your Adobe Photoshop ﾔPlug-insﾕ folder and, optionally, inside the ﾔFile Formatsﾕ folder within the ﾔPlug-insﾕ folder. PhotoGIFｪ will then be available to use as a method to open and save files the next time Photoshop is restarted. ﾔPhotoGIFｪﾕ will then appear as a new item in the file format menu in Photoshopﾕs open file and save file dialogs.
PhotoGIFｪ is a FAT plug-in and will run in native mode on both 68k and PPC based Macintosh computers for best performance.
The PhotoGIFｪ Interface
PhotoGIFｪ has many capabilities, and its interface is comprised of many different dialogs, unlike most plug-ins that only have one dialog that controls all functions of the plug-in. There are 14 dialogs in PhotoGIFｪ, 11 of which control the operation of the plug-in. Below is a hierarchy of the dialogs in PhotoGIFｪ.
･ The about box dialogs
･ The preferences
･ The credits
･ The support
･ Multi-image open options dialog
･ Open image picker
･ Palette options dialogs
･ Palette get file
･ GIF palette picker
･ Color reduction options
･ The single-image options dialogs
･ Appending get file
･ Appending insertion picker
･ Multi-image options
Using PhotoGIFｪ to perform a ﾔSave as...ﾕ on an image minimally requires one dialog, the single-image options dialog, if saving from bitmapped, grayscale, or indexed mode and at most, seven dialogs if saving from RGB mode, loading an existing palette from a multiple image GIF file for color reduction, appending the file being saved to an existing GIF file and resetting the multiple image options for an animation at the same time.
The Multi-image open options dialog
The multi-image open options dialog allows you to choose what method with which to open a multi-image GIF file. It will only be presented if the file being opened contains multiple images. If the file being opened does not contain multiple image no dialogs will appear when opening the file.
There are four methods that can be used when opening multiple image GIF files: ﾔEdit single image...ﾕ, ﾔEdit in cell-strip formatﾕ, ﾔExtract single image...ﾕ, ﾔExtract all imagesﾕ. Methods ending with ﾔ...ﾕ signify that a second dialog is required for that method.
- Edit single image
Opening a multiple image GIF animation file with the ﾔEdit single image...ﾕ method opens a single image from a multiple image GIF animation file to edit, while preserving the multiple image structure of the original GIF animation file. If you select ﾔEdit single image...ﾕ from the multi-image open options dialog, a second image picker dialog will be presented for you to preview the individual images contained in the multiple image GIF animation file and choose which image to edit.
- Edit in cell-strip format
Opening a multiple image GIF animation file with ﾔEdit in cell-strip formatﾕ method causes all of the images contained in the multiple image GIF animation file to be opened into one document oriented either horizontally or vertically. This method also preserves the multiple image structure of the file upon saving. The ﾔEdit in cell-strip formatﾕ method will only be available as an option if all the images in the multiple image GIF animation file use a common, global palette. If any image from the file uses a different palette from the other images, this option will be disabled. Note that ﾔEdit in cell-strip formatﾕ will add redundant information to your multiple image GIF animation files if they are not composed of images that are the full logical size of the animation.
- Extract single image
The ﾔExtract single imageﾕ method does not open the original file. It creates a new single image GIF file of the image selected from the multiple image GIF animation file, then opens the new file for editing. The new file created is always placed in the same folder containing the original file. If you select ﾔExtract single image...ﾕ from the multi-image open options dialog, a second image picker dialog will be presented for you to preview the individual images contained in the multiple image GIF animation file and choose which image to extract from the original multiple image GIF animation file.
- Extract all images
The ﾔExtract all imagesﾕ method does not open the original file. It creates a new single image GIF file for every image contained in the original multiple image GIF animation file and then opens all of the new files for editing. The new files created will always be placed in the same folder containing the original multiple image GIF animation file.
- The Open image picker
The open image picker dialog is presented only if the ﾔEdit single image...ﾕ or ﾔExtract single image...ﾕ methods are chosen from the Multiple image options dialog. The open image picker dialog allows you to preview the images contained in a multiple image GIF animation file in order to choose which image to open or extract.
The current image and number of images contained in the multiple image GIF animation file is displayed in the title of the group box surrounding the image preview.
The checkbox labeled ﾔShowﾕ controls the visibility of the image preview in the open image picker dialog. When it is checked the preview will be visible, and when it is unchecked the preview will not be visible.
The spinner control, beneath the preview in the open image picker, allows you to step forward and backwards though the images contained in the multiple image GIF animation file. The sequential number of the currently selected images will be displayed in the title of the group box surrounding the preview, as well as in the edit text box next to the spinner control. You may also enter the number for which image to preview in the edit text box.
Color reduction options
When using PhotoGIFｪ to save a file from RGB mode the first dialog that is presented, not including Photoshopﾕs put file dialog where you supply the name of the file and designate the location to place the file, is the color reduction options dialog.
When saving to GIF from RGB mode the image must first be color reduced to 256 colors or less, because the GIF format supports a maximum of 256 unique colors in an image. The color reduction options dialog allows you to choose first whether color reduction will be performed by generating a custom palette or by using an existing fixed palette. This is controlled by the group of two radio button in the top, left of the dialog labeled ﾔGenerate custom paletteﾕ and ﾔUse fixed paletteﾕ, respectively.
If using an existing fixed palette, the color reduction options dialog allows you to choose any palette from the ﾔPaletteﾕ pup-up menu and displays the palette in the dialog. The Mac system palette, a gray scale palette, and the infamous Netscape palette are built in options for fixed palettes. You may also use the ﾔLoadﾕ button across from the ﾔPaletteﾕ pop-up menu to load any palette from a GIF file or Photoshop CLUT file or to unload any palette from the ﾔPaletteﾕ menu by depressing the ﾔoptionﾕ key. When you press the ﾔoptionﾕ key, the ﾔLoadﾕ buttonﾕs title will change to ﾔUnloadﾕ and hitting the ﾔUnloadﾕ button will remove the current palette from the ﾔPaletteﾕ menu.
When using both custom and fixed palettes for color reduction, you must specify the depth or number of colors desired. Any number of colors between 2 and 256 is valid and there are preset radio buttons for even bit depths of 256 (8 bit), 128 (7 bit), 64 (6 bit) and 32 (5 bit) colors in the ﾔResolutionﾕ group box. Any other valid number of colors between 2 and 256 may be used by selecting the ﾔOtherﾕ radio button in the ﾔResolutionﾕ group box and entering the desired number of colors in the corresponding edit text field.
The last set of controls in the color reduction options dialog controls dithering. The dithering in PhotoGIFｪ is unlike other dithering methods you may be familiar with that are either ﾔonﾕ or ﾔoffﾕ. To improve both image quality and compression PhotoGIFｪ uses a new variable magnitude, selective dithering method. Dithering can be turned on or off with the ﾔDitherﾕ checkbox. This method of dithering allows control over the magnitude of dithering used for the particular image with the ﾔMagnitudeﾕ slider, and where dithering is applied is controlled internally and limited to only where necessary instead of the entire image. The range of the ﾔMagnitudeﾕ slider is -5 to 5, with 5 being the maximum amount of dithering possible. Lower settings will result in smaller files, but higher ones will generally result in better looking files. Settings between 0 and 3 usually work best as a happy medium between image quality and file size.
The palette get file dialog
If you hit the ﾔLoadﾕ button from the color reduction options dialog, the palette get file dialog is displayed. This is a standard dialog for selecting the GIF or Photoshop CLUT file containing the palette you wish to load. It will alternately display a list of GIF files or a list of Photoshop CLUT files depending on whether the ﾔGIF fileﾕ or ﾔCLUT fileﾕ radio button is selected.
Select the file you wish to load a palette from by double-clicking it in the file list or hitting the ﾔOpenﾕ button while the file is highlighted in the file list. You may also cancel loading a palette from the palette get file dialog, and you will be returned to the palette options dialog without canceling the entire saving process.
If you select a GIF file containing multiple palettes the next dialog that will be presented is the GIF palette picker dialog. If you select a GIF file containing only a single palette or a Photoshop CLUT file the next dialog will be the fixed palette color reduction options dialog.
The GIF palette picker dialog
The GIF palette picker dialog is presented only if you select a GIF file containing multiple palettes from the palette get file dialog, when loading a fixed palette.
The GIF palette picker dialog allows you to preview the palettes contained in a GIF file that contains multiple palettes in order to chose which palette you wish to load.
The current palette and number of palettes contained in the file are displayed in the title of the group box surrounding the palette preview. The checkbox labeled ﾔShowﾕ controls the visibility of the palette preview in the GIF palette picker dialog. When it is checked the preview will be visible, and when it is unchecked the preview will not be visible.
The spinner control beneath the palette preview in the GIF palette picker allows you to step forward and backwards though the palettes contained in file. The sequential number of the currently selected palette will be displayed in the title of the group box surrounding the palette preview, as well as in the edit text box next to the spinner control. You may also enter the number for which palette to preview in the edit text box.
When you have chosen what palette to load from the file, hitting the ﾔOKﾕ button in the GIF palette picker dialog will load the currently selected palette and return you to the palette options dialog. You may also cancel and not load a palette with the ﾔCancelﾕ button, which will also return you to the palette options dialog.
The single image options dialog
The single image options dialog is the main dialog in PhotoGIFｪ. It allows you to preview your image, set interlacing, transparency and gives you the option to show additional dialogs for creating multiple image GIF animation files.
- The preview
The preview allows you to see the effects of color reduction if saving from RGB mode, the effects of transparency settings and an editing window for the advanced transparency tools. The default position of the preview area is the top, left portion of the image. The horizontal and vertical scroll bars can be used to change the preview area to any portion of the image being saved.
- The transparency tools
To the left of the horizontal scroll bar are the transparency tools. They are the brush tool, the dropper tool, and the edge tool, respectively.
The brush tool is for removing transparency artifacts that are away from the edges of your transparency such as speckles in the transparent area.
The dropper tool is used to select the transparent color when using the color transparency method. The dropper can be used to pick a color from the image visible in the preview or from the image palette. Only one transparent color can be selected at a time with the dropper tool.
The edge tool can be used to easily and quickly remove unwanted halo effects from the edges of your transparency caused by antialiasing. The edge tool works much like a brush except that absolute precision is not required. The position of the edge tool is only used by PhotoGIFｪ as a starting point to determine the location of the intended edge of the transparency in your image and the length of the edge that has the unwanted halo effect. The operations performed to remove the halo effect after the affected edge has been located with the edge tool are automatic. One pass with the edge tool is generally all that is required to achieve perfect transparency edges.
NOTE: The brush and edge tools operate on a transparency mask maintained internally by PhotoGIFｪ and do not actually change the image data in the preview or the original image data maintained by Photoshop. If you switch between transparency methods after using the brush or edge tools to correct transparency the changes will be lost. Also, note that changes made in the preview using the brush or edge tools will not change the original open image and those changes will be reverted if you ﾔSaveﾕ the open image again. You should close the image, and reopen it to make permanent the changes made using the brush or edge tools.
- The transparency method
Beneath the preview is the ﾔTransparency methodﾕ group box. Using PhotoGIFｪﾊthere are three possible transparency methods, ﾔAlphaﾕ, ﾔColorﾕ, and ﾔNoneﾕ that are set with the radio buttons in the ﾔTransparency methodﾕ group box.
When the ﾔAlphaﾕ radio button is selected, PhotoGIFｪ will use a saved alpha channel as a transparency mask. This may be any alpha channel in the working document, and when the ﾔAlphaﾕ radio button is selected, a popup menu will appear to the left of the ﾔAlphaﾕ radio button for you to select an alpha channel. Note that if there are no alpha channels present, the ﾔAlphaﾕ radio button will be disabled.
When the ﾔColor' radio button is selected, PhotoGIFｪ will use the color selected with the dropper tool as the transparent color of the GIF file being saved. The decimal and hexadecimal values for the current transparent color will be displayed next to the ﾔColorﾕ radio button and the current transparency color will also be displayed in a large color swatch beneath the values for the selected color.
- The ﾔShow multi-image options dialogﾕ check box
The ﾔShow multi-image options dialogﾕ check box controls whether the dialog for setting options, required for saving multiple image GIF animation files, will be shown.
- The ﾔAdd to existing GIF fileﾕ check box
The ﾔAdd to existing GIF fileﾕ check box controls whether additional dialogs, required for appending files together to create multiple image GIF animation files, will be shown. When this option is checked two radio buttons, ﾔCreate local paletteﾕ and ﾔFactor into global paletteﾕ, will become active. These control how the palette for the image being saved will be handled, when it is merged with the existing file. ﾔCreate local paletteﾕ causes a local palette to be used for the image being saved. ﾔFactor into global paletteﾕ performs super palette factoring, thus creating a new global palette the multiple image GIF file being created or added, that best represents all the images within the multiple image file.
- The image size read out
The image size readout is the top text line above the palette and is simply a display of the dimensions of the image being saved as pixels-wide by pixels-high.
- The bit-depth read out
The bit-depth readout is the text line directly above the palette. The bit-depth read out displays the lowest depth in bits at which the image can be saved and the number of used colors in the image, which may be fewer than the number of colors contained in the displayed palette.
- The palette
The imageﾕs palette is always displayed. PhotoGIFｪ will not change the ordering of colors in the palette, nor remove colors from the palette when the image is saved. This ensures the integrity of palette indexes for multiple image GIF animation applications and when application dependent palettes, such as the Netscape palette, are used.
- The ﾔOptimize palette usageﾕ check box
ﾔOptimize palette usageﾕ is a lossy option that further reduces the number of colors used in the image to compensate for palette redundancy and to improve compressibility. The number of colors removed from the image will vary and is automatically determined, based on the values of the colors in the imageﾕs palette. This option does change the appearance of the image being saved and, at times, can cause noticeable loss in image quality, particularly if there are large, smoothly changing gradients in the image. ﾔOptimize palette usageﾕ does allow a very significant saving in file size, but it should be used with caution. It is not recommended to save an image multiple times with the ﾔOptimize palette usageﾕ. Note that if ﾔPalette optimizationﾕ is used, PhotoGIFｪ immediately defaults to no ﾔPalette optimizationﾕ for subsequent ﾔSaveﾕ operations.
- The ﾔInterlaceﾕ check box
To the right beneath the palette is the ﾔInterlaceﾕ check box. Interlacing allows for the incremental display of GIF images as they download and gives the effect of faster downloading of your image. Note that it is not advisable to save images that are part of multiple image GIF animation files with interlacing.
- The ﾔBrowser background colorﾕ RGB sliders
The group box titled ﾔBrowser background colorﾕ contains a set of RGB sliders for setting the color that will be used as your web page background color. Note that this is not the same background color as the background color of your GIF file which can be set in the multiple image options dialog.
The browser background color is to allow accurate preview of how your image will look as a transparent GIF and also has effect on how the edge tool operates. You should accurately set the browser background color to the color you intend to use on the page that will contain the image being saved or the results of setting the image's transparency may be different than those you expect.
Each of the sliders in the ﾔBrowser background colorﾕ group box has a corresponding text edit item that a decimal value can be directly entered in. Note that the sliders themselves are limited to even numerical values and odd numbers must be entered as text. The hexadecimal value of each color component is also displayed.
Appending get file dialog
If you check ﾔAppend to existing fileﾕ in the single image options dialog, the next dialog shown is the appending get file dialog. This dialog is a standard get file dialog that will allow you to select an image to combine with the image being saved. Note that the file selected in the appending get file dialog is left unmodified, as the images are combined into the file being saved.
Appending insertion picker
The appending insertion picker dialog allows you to specify where to put the image you are saving into the multiple image file, being created or modified. It is shown after the appending get file dialog.
The appending insertion picker dialog allows you to preview the images in the file. The sequential number of the currently selected image within the multiple image GIF file is also displayed in the title of the group box surrounding the preview. The check box titled ﾔShowﾕ at the bottom, left of the preview group box, controls the visibility of the image preview. The spinner control to the right of the ﾔShowﾕ checkbox steps forward and backward through the images contained in the multiple image GIF animation file. The edit text box next to the spinner control allows you to enter the number of the image directly.
There are three choices for the insertion point of the image being saved. ﾔAfter all imagesﾕ inserts the image being saved into the multiple image GIF animation file after all images currently in the file. ﾔBefore all imagesﾕ inserts the image being saved into the multiple image GIF animation file before all images currently in the file. ﾔAfter selected imageﾕ inserts the image being saved after the image currently selected in the preview.
Multiple image options dialog
The multiple image options dialog allows you to control settings that are specific to creating GIF animations such as logical screen size, image position, delay time, disposal method, looping and the GIF background color.
The logical screen size of a GIF animation is the size of the area in which the animation will be played. It can be larger than the dimensions of the largest image within the multiple image GIF animation file, but the logical screen size may not be so small that it will not contain the entirety of all images in the multiple image GIF animation file, taking into account the position of the images. PhotoGIFｪ will automatically increase the logical image size to insure that it is large enough to contain all images within the multiple image GIF animation file, but should PhotoGIFｪ have to increase the logical image size, your images within the multiple image GIF animation file may no longer be positioned where you intend within the logical screen size. It is good practice to plan well enough in advance when creating a multiple image GIF animation file that the logical image size will not have to be adjusted afterward to accommodate a larger image or the position of an image.
The position of the image being saved is the horizontal and vertical offset from the top, left corner of the logical screen bounds. Individual images within a multiple image GIF animation file do not have to be the same size and can be positioned anywhere within the logical screen bounds.
The looping value applies to the whole multiple image GIF animation and is not specific to the individual image being saved. It is the number of times the animation is expected to play, before stopping.
The delay time is the length of time of delay after an individual image in the animation is rendered before beginning to render the next image in the animation. Delay time is measured in 1/100ths of a second, so a delay value of 100 would result in a 1 second delay for the specific frame of the animation.
The disposal method determines how the individual image is removed or not removed after display, as the GIF animation plays. There are four available disposal methods and an option for requiring user input before proceeding available.
Disposal methods
- ﾔUnspecifiedﾕ
This disposal method lets the viewing application determine how the image will be disposed in the animation and may vary in result, depending on what viewing application is used to play the multiple image GIF animation.
- ﾔDonﾕt Disposeﾕ
This disposal method leaves the image in place and the subsequent image from the multiple image GIF animation will be rendered on top of the image left in place.
- ﾔRestore background colorﾕ
This disposal method removes the image and replaces it with the GIF background color before rendering the next image from the multiple image GIF animation file.
- ﾔRestore previous contentsﾕ
This disposal method removes the image and replaces it with the previous contents, there before the image was rendered, before rendering the next image in the multiple image GIF animation file.
- ﾔRequire user inputﾕ
This is an optional flag that can be set with any disposal method that signals the viewing application to wait for user input, before proceeding to dispose of the current image and rendering the next image from the multiple image GIF animation file. The type of action for ﾔuser inputﾕ is defined by the viewing application.
Note, that not all disposal methods are supported by all viewing applications. If the set disposal methods do not appear to be functioning properly when viewing it is because they are not supported in the viewing application.
Preferences
PhotoGIFｪ has the most advanced preferences capabilities of any Photoshop plug-in. The default behavior of nearly every aspect of opening and saving single image GIF files and multiple image GIF animation files is controllable through preference settings. In PhotoGIFｪ the preferences dialog is available from the plug-in about box. This is accessed from the Apple menu. While Photoshop is running in the foreground the first menu item under the Apple menu is ﾔAbout Photoshop...ﾕ and directly beneath that is a hierarchical menu item, ﾔAbout plug-inﾕ. When you select ﾔAbout plug-inﾕ from the Apple menu, a hierarchical menu will be shown to the left of the Apple menu with a list of plug-ins in it. ﾔ PhotoGIFｪ...ﾕ will be one of the top items in this menu and selecting the ﾔ PhotoGIFｪ...ﾕ item from the hierarchical menu of plug-ins will cause the PhotoGIFｪ about box to be displayed.
In the about box there are four buttons, ﾔCredits...ﾕ, ﾔSupport...ﾕ, ﾔPreferences...ﾕ and ﾔDoneﾕ. The ﾔCredits...ﾕ button displays the credits screen. The ﾔSupport...ﾕ button displays the contact information for technical support for PhotoGIFｪ. The ﾔPreferences...ﾕ button displays the preferences dialog for PhotoGIFｪ. The ﾔDoneﾕ is equivalent to an ﾔOKﾕ button, and makes the about box go away.
The preferences dialog for PhotoGIFｪ has four separate panels for controlling various aspects of the plug-inﾕs behavior. Individual panels are accessed from the popup menu in the top, left of the preferences dialog. The panels accessible from the popup menu are ﾔReadingﾕ, ﾔImage optionsﾕ, ﾔMulti-optionsﾕ, and ﾔQuantizationﾕ.
- The ﾔReadingﾕ panel
The ﾔReadingﾕ panel controls default behavior for opening multiple image GIF animation files. The settings in the ﾔReadingﾕ panel correspond directly to the controls in the Multi-image open options dialog and allow you to choose the default editing method for multiple image GIF animation files.
- The ﾔImage Optionsﾕ panel
The ﾔImage optionsﾕ panel corresponds directly to settings in the single image options dialog and allows you to set default behavior for whether to show the multiple image options dialog after the single image options dialog; optimizing palette usage; transparency; interlacing; and whether the dialogs for adding the file being saved to an existing file, to create a multiple image GIF animation file, will be shown by default.
- The ﾔMulti-Optionsﾕ panel
The ﾔMulti-optionsﾕ panel corresponds directly to settings in the multiple image options dialog and allows you to set default values for disposal method, looping, and delay time.
- The ﾔQuantizationﾕ panel
The ﾔQuantizationﾕ panel applies to the color reduction options dialog. The ﾔQuantizationﾕ panel allows you to set default values for color reduction method, the resolution, and dithering.
Canceling from the preferences dialog at any point will return you to the about box for PhotoGIFｪ without changing any of the PhotoGIFｪ saved preference settings. Hitting the ﾔOKﾕ button will save the new preferences settings if you have made changes and will also return you to the about box for PhotoGIFｪ. To exit the about box, hit the ﾔDoneﾕ button.
Opening Files with PhotoGIFｪ
Opening files with PhotoGIFｪ takes no special action from the finder. Simply double-click on or drag a GIF file onto Photoshop, and PhotoGIFｪ will be used as the default method for opening all GIF files. There is no user control over this behavior, and there are no variants of GIF files that PhotoGIFｪ cannot open.
PhotoGIFｪ automatically determines if a GIF file contains one or multiple images. If the file is a single image GIF file, no additional user input is required, and the file is opened directly into Photoshop without any dialogs being presented. However, if PhotoGIFｪ determines that the file being opened contains multiple images, additional input is required before the file can be opened, and the multiple image open options dialog is presented.
The multiple image open options dialog allows you to specify the mode in which you would like to edit the multiple image file. There are four editing modes available, each having its specific advantages for working with multiple image GIF animation files.
The first mode ﾔEdit single image...ﾕ allows you to directly edit one image within a multiple image GIF animation file while maintaining the integrity of the multiple image structure of the original file. If you select ﾔEdit single image...ﾕ as the editing mode, an additional dialog, the open image picker, will be displayed after the multiple image open options dialog so you can select which image from the multiple image GIF animation file to open.
The second mode ﾔEdit cell-stripﾕ is most useful for viewing all the images within a multiple image GIF animation file at the same time. It is not suitable for editing animations, unless all the images within the animation are the same size as the logical screen size of the multiple image GIF animation file. If any of the images within the multiple image GIF animation file are smaller than the logical screen size of the multiple image GIF animation file, reserving the file from ﾔEdit cell stripﾕ mode will increase the size of the file, because the images smaller than the logical screen size will be increased in size by filling the area between the image size and the logical screen size with the GIF background color. You can view either vertically or horizontally in ﾔEdit cell-stripﾕ mode.
The third mode ﾔExtract single image...ﾕ allows you to extract a copy of a single image contained within a multiple image GIF animation file to edit. The original file will be left unaltered and a new single image GIF file will be created and opened into Photoshop for editing. The new file created is automatically named with the original file name and the sequential number of the image being extracted. If a file already exists with this name, PhotoGIFｪ will return an error. If you select ﾔExtract single image...ﾕ as the editing mode, an additional dialog, the open image picker, will be displayed after the multiple image open options dialog so you can select which image from the multiple image GIF animation file to extract.
The fourth and last editing mode, ﾔExtract all imagesﾕ operates in much the same way as ﾔExtract single image...ﾕ except that all images are extracted into new single image GIF files and then opened into Photoshop for editing. The new files created are automatically named with the original file name and the sequential number of the image contained in each new file. If a file already exists with the same name as PhotoGIFｪ tries to assign to a new file, PhotoGIFｪ will return an error and will not extract the corresponding image from the multiple image GIF animation file. The original multiple image GIF animation file is not altered.
Saving Files with PhotoGIFｪ
There are two means of saving files using PhotoGIFｪ. The first is using the ﾔSave as...ﾕ command in Photoshop and the second is ﾔSaveﾕ or Command - S. You should be very familiar with save and save as from within Photoshop and using PhotoGIFｪ works in much the same way as saving in other formats from Photoshop, except in some cases when performing a ﾔSaveﾕ requires user input not present with other formats.
If you perform a ﾔSave as...ﾕ, you first see Photoshopﾕs put file dialog where you select the format to use and supply the name for the new file. Once you hit the ﾔSaveﾕ button in that dialog, PhotoGIFｪ will show the required options dialog for the saving process. Which dialog shown immediately after Photoshopﾕs put file dialog depends on the image mode of the working image within Photoshop.
PhotoGIFｪﾊsupports saving from bit-mapped, greyscale, indexed and RGB image modes. When performing a ﾔSave as...ﾕ from bit-mapped, greyscale, or indexed image mode, the first dialog presented by PhotoGIFｪﾊis the single image options dialog. However, if performing a ﾔSave as...ﾕ from RGB mode, the working image must first be color-reduced, because the GIF format supports a maximum of 256 colors per image, and the first dialog presented will be the color reduction options dialog.
In the color reduction options dialog you specify whether to use a custom palette optimized for the individual image or an existing fixed palette when color-reducing the image. You can also load any palette from any existing GIF file or Photoshop CLUT file by using the ﾔLoadﾕ button in the color reduction options dialog.
You need to specify the resolution or number of colors desired in the color reduction options dialog. When using a custom palette, most images can be represented very effectively using a low number of colors, 32 or 64 will accommodate most images using the custom palette color reduction in PhotoGIFｪ. However, color reduction is more difficult when using an existing fixed palette because the palette may not be well suited to the image. The fixed palette color reduction in PhotoGIFｪ is more advanced than that found in other applications and will generally do a much better job of color reduction using an existing palette, but the results will still vary greatly depending on the palette and how suited it is to the image.
You also need to set controls for dithering. There is a check box to turn dithering on/off and a slider control to set the level of dithering. Higher values for dithering with the fixed palette color reduction can improve visual quality, but will adversely affect file size. Dithering should be set to the lowest acceptable value for image quality to achieve the smallest GIF file size, and the amount of dithering necessary will vary with the image being color-reduced.
The single image options dialog will be displayed immediately after Photoshopﾕs put file dialog if you are saving from bit-mapped, grayscale, or indexed image modes in Photoshop, or immediately after the color reduction options dialog previously displayed, if saving from RGB image mode in Photoshop.
The single image options dialog is the primary dialog for PhotoGIFｪ, and the last dialog required if saving a single image GIF file. In the single image options dialog, you set GIF image parameters for transparency, as well as interlacing, have control over palette usage optimization, and whether you require the dialogs for creating and editing multiple image GIF animation files.
Setting transparency is the primary function of the single image options dialog. There are three tools that allow you to get flawless transparency for your GIF images, and PhotoGIFｪ can also use any saved alpha channel to designate transparency in the image.
To use an alpha channel to set transparency, you will need to select the portion of the image that you DO NOT want to be transparent, and save that selection to an alpha channel before using PhotoGIFｪ to save the file. Using an alpha channel provides the most accuracy and control for setting transparency and is also the simplest way to set transparency if the portion of the image you want to make transparent contains many different colors. Once in the single image options dialog to set transparency using a saved alpha channel, select ﾔAlphaﾕ as the transparency method and pick the alpha channel you saved for transparency with the popup menu that appears when you select the ﾔAlphaﾕ transparency method. You will see how your image will look with transparency set with the saved alpha channel in the preview.
To set transparency based on a color, first select ﾔColorﾕ as the transparency method, then use the dropper tool to select the transparent color from either the preview or the palette. The preview will always show exactly how your image will display as a transparent GIF, but it is important that you use the RGB sliders for browser background color to set the actual color you intend to use on your web page for the preview. Visual halo effects around the edges of your transparency are directly related to the browser background color and if a different browser background color is used to preview the image than the actual color used on the web page the image will appear on then there is no guarantee that the edges of your transparency will appear clean and free from unwanted halo effects.
To remove halo effects from the edge of your transparency, use the edge tool. Exact precision in not necessary when using the edge tool. Simply trace the outline of your image with the edge tool and halo effects will be automatically removed. Note that the operation of the edge tool is dependent on the correct browser background color being set in the single image options dialog.
If you do not want to save a transparent GIF, check ﾔNoneﾕ for the transparency method.
After setting transparency, you should set interlacing for the image. Large single image GIF files should generally be interlaced since interlacing lets viewers see the image faster as it downloads. Very small single image GIF files and images within multiple image GIF animation files should generally not be interlaced.
From the single image options dialog, you can also select the ﾔOptimize palette usageﾕ option. This option will remove redundant colors from the image being saved and significantly improve file size. It is a lossy option and can result in possibly loss of image quality if used on images with large, smooth gradients. On most images no unacceptable loss of image quality will occur, but it should be used with caution.
If you are saving a single image GIF file, make sure that the ﾔShow multi-image options dialogﾕ and ﾔAdd to existing GIF fileﾕ checkboxes are NOT checked. If PhotoGIFｪ goes through the multi-image options dialog, it will add the Netscape looping extension block to the saved GIF image. In certain versions of Netscape this will cause your single image to continuously reload and redraw.
Saving Multiple Image GIF animation Files with PhotoGIFｪ
PhotoGIFｪ creates multiple image GIF animation files by appending the contents of an existing single or multiple image GIF file together with the image being saved.
There are three dialogs that control saving multiple image GIF animation files. The multiple image options dialog allows setting GIF animation parameters for looping, delay time, logical screen size, position and disposal method; while, the appending get file dialog and the appending insertion picker dialog work together to allow you to combine images together into multiple image GIF animation files.
These dialogs are optionally shown, depending on whether ﾔShow multi-image optionsﾕ or ﾔAppend to existing GIF fileﾕ are checked in the single image options dialog.
To create a multiple image GIF animation file, begin with a single image that will be the first image in your animation and save it with PhotoGIFｪ. Make sure to check the ﾔShow multi-image options dialogﾕ check box from the single image options dialog, but not the check box for ﾔAppend to existing GIF fileﾕ.
In the multiple image options dialog, set the initial global parameters for looping, logical screen size, and background color. These can be changed at any time while building the multiple image GIF animation file. Also set the local parameters for delay time on the image being saved, the position of the image relative to the logical screen size and the disposal method.
The file will be saved with all the required information for a multiple image GIF animation file, but you will need to add more images to create a multiple image GIF animation file. To do this close the image just saved and open the next image you want to use in your animation. Follow the same steps when saving it but in addition to checking ﾔShow multiple image options dialogﾕ from the single image options dialog, also check ﾔAppend to existing GIF fileﾕ.
After the single image options dialog, the appending get file dialog will be presented. Select the image you saved previously for the first image in your animation by double clicking it in the file list. The appending insertion picker dialog will then be presented. You can chose to insert the second image before or after the first image you saved. If you there is more than one image in the file you are combining to the file being saved, you can also choose to insert the new image after any image in the existing multiple image GIF animation file.
After you have selected the insertion point for the current image being saved, the multiple image options dialog will be shown so you can set the local parameters for the image being added to the multiple image GIF animation file and change global parameters, if necessary.
The image being saved becomes a multiple image GIF file containing more images and the file selected in the appending get file dialog remains unmodified. The last file saved will be your completed multiple image GIF animation file, and all other files will remain as intermediate steps in creating your animation.
NOTE: There are limitations to PhotoGIFｪﾕs editing ability with multiple image GIF animation files. Although, it is easy to add images to your animations, there is no good way to change the ordering of the images within a multiple image GIF animation file or remove an image from a multiple image GIF animation file with PhotoGIFｪ at present. The cell strip editing mode does provide a primitive way to change the ordering of images and to remove an image but it requires careful selecting of the image area and also careful changing of the working documentﾕs canvas size, while editing the multiple image GIF animation file in cell-strip mode.
PhotoGIFｪ is the only tool that provides direct editing capability for images within GIF animations and also the only easy way to separate images from multiple image GIF files into single images again but, GIFmationｪ, another BoxTop Software, Inc. tool, is a video editor for GIF animations that provides more advanced capabilities for editing GIF animations and preview capability that is not present in PhotoGIFｪ.
Optimizing GIF images for the web with PhotoGIFｪ
GIF files use a lossless compression method called LZW that is an efficient general purpose compression algorithm. Image data is encoded a scan line at a time and LZW compression efficiency is closely related to the amount of linear change in the scan lines of the image being compressed.
Dithering, a common technique to improve the quality of indexed color images, adds entropy, or change, that makes the LZW compression used by GIF less efficient. Dithered images will generally compress as well as non-dithered images. The custom palette color reduction in PhotoGIFｪ does not use traditional dithering techniques, it uses a variable intensity selective dithering method that minimizes the entropy added to the image by dithering and thus improves compressibility as much as possible while still ensuring satisfactory visual quality.
Aside from dithering and the entropy it causes that adversely affects the compressibility of image data, the biggest factor effecting image size is resolution, or bit-depth of the image. The lower the bit-depth and fewer number of colors used in an image, the smaller it will compress as a GIF file. PhotoGIFｪ has superior custom and fixed palette color reduction that allows you to achieve acceptable visual results, while using fewer colors in images. This capability will allow you to create smaller GIF files that download and display faster.
In addition PhotoGIFｪ has optimization features that automatically find and remove redundant colors in the palette from the image being saved. This can result in unwanted quality loss for images with smooth gradients but for most images the effects are not visually apparent, while the effects on file size are significant.
Beyond the capability built into PhotoGIFｪ, GIF images can be optimized by hand to improve their compressibility. This is not a fast process but it is an easy one that can make a very large difference in file size at times. By manually removing areas of horizontal change in the scan lines of an image to be saved as GIF files, you can make a very noticeable difference in file size with no question of image quality.
PhotoGIFｪ 2.0 is Copyright 1996 BoxTop Software, Inc. All rights reserved. PhotoGIFｪ is a Trade Mark of BoxTop Software, Inc.
