PhotoGIFェ Text Docs 1. Copyright 1996 BoxTop Software, Inc. All rights Reserved.
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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.
(Continued in "PhotoGIFェ Text Docs 2")
PhotoGIFェ 2.1 is Copyright 1996 BoxTop Software, Inc. All rights reserved. PhotoGIFェ is a Trade Mark of BoxTop Software, Inc.