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L O O K E R I m a g e P r o c e s s o r Copyright 1987 by Frederick Hawkins LOOKER may be freely distributed as long as this document accompanies it. ________ Q U I C K R E F E R E N C E __________________________________ File L LOAD .PI1, .PI3, .DTH S SAVE .PI3, .DTH Palette [Clr Home] START a new palette list. [Insert] ADD to a palette list. [Undo] DISCARD palette list. [Up,Down] SELECT a color to change. [Right] LIGHTEN the halftone of a palette color or palette list. [Left] DARKEN the halftone. [1 to 9] Set INCREMENT used by Lighten and Darken. N Show a NEGATIVE view of a color. R RESET palette to default values. Z ZERO all other palette values. Transform A Show ALTERNATIVE settings. C COPY current settings to ALTERNATE. D DITHER. G GRAY. H HALFTONE. T Change Dither TYPE. X MEZZOTINT. [0 zero] Perform TRANSFORM. Buffers [cr] Toggle between MAIN and WORK. K View KEEP buffer. [*] ERASE Keep buffer. [+] SET Keep with Work buffer. [-] CLEAR Keep with Work buffer. [/] STRIKE last Keep buffer change. System [#] Load TEST pattern. [Help] HELP. I INSTALL or change Dither tables. Q QUIT. M MAGNIFY. V VERSION. [&] Trap to SID. ________C O M M A N D S alphabetical_________________________________ [Clr Home] START a new palette list. Palette [Help] HELP. System [Insert] ADD to a palette list. Palette [Left] DARKEN the halftone. Palette [Right] LIGHTEN a color or list. Palette [Undo] DISCARD palette list. Palette [Up,Down] SELECT a color to change. Palette [/] STRIKE last Keep buffer change. Buffer [-] CLEAR Keep with Work buffer. Buffer [+] SET Keep with Work buffer. Buffer [*] ERASE Keep buffer. Buffer [&] Trap to SID. System [#] Load TEST pattern. System [cr] Toggle between MAIN and WORK. Buffer [0 zero] Perform TRANSFORM. Transform [1 to 9] Set INCREMENT. Palette A Show ALTERNATIVE settings. Transform C COPY settings to ALTERNATE. Transform D DITHER. Transform G GRAY. Transform H HALFTONE. Transform I INSTALL Dither tables. System K View KEEP buffer. Buffer L LOAD a .PI1, .PI3, .DTH file. File M MAGNIFY. System N Show NEGATIVE. Palette Q QUIT. System R RESET palette to default. Palette S SAVE a .PI3, .DTH file File T Change Dither TYPE. Transform V VERSION. System X MEZZOTINT. Transform Z ZERO all other palette values. Palette WHAT? LOOKER interactively transforms low resolutiooon image to a high resolution image. BUTS No GEM, no alerts, no buttons, no menus, no C, no PASCAL, no MODULA2, not for color systems (not enforced), not a slide show, no mouse, not a well-behaved application, not a replacement for TINYSTUF or PICSW6 or GRAFCON. NOT YET Medium resolution load and transforms, rotate, zoom, mouse draw/erase, high resolution load as pseudo-low resolution, John Brochu's any-type file load (thanks, John!), printing, image placement, disk directory, RLE compression in memory, frame transforms. ________F O R E G R O U N D _______________________________________________ LOOKER can selectively convert each individual color in a low resolution image. Transforms include a middle gray, a mezzotint, a five-level halftone and eight preset dithering patterns of 64 gray levels. These dithering patterns may be interactively changed, saved and loaded. Entire colors may be eliminated or set to black. The high resolution output file may be just the default transformation. Or it can be assembled from one or more images. Mixing of halftoning methods within a single image is possible and encouraged. Side by side comparisons of different settings and/or halftone methods are easily accomplished. Colors in the original may be linked together so that all may be darkened or lightened equally, thus holding their relations. ________B A C K G R O U N D _________________________________________________ Memory management: LOOKER maintains two screen buffers, two sub-screen buffers and an input file block, giving an overhead of 100K. This version can run out of 220K ramdisk with NO desk accessories on a 520. LOOKER takes all of the memory that TOS gives it and assumes that the memory between it and the desktop screen is available. LOOKER doesn't mess with anything below itself, nor does it use any interrupts. Inputs in general: Pressing [Return] or [Enter] will accept the default reply. A 'n/y' stands for a simple no/yes -- and the default will have the cursor on it. Prompts for filenames and pathnames are separate. LOOKER doesn't force either case. LOOKER uses the ST's keyboard buffering and pulls keystrokes off until it gets caught up. On occasion, LOOKER has crashed when overloading the buffer (more than 64 characters, I think). Key sequencing is nevertheless useful. Moving up or down one Palette table entry takes about a second, owing to the overhead in calculating the micro screen. Shooting past the desired entry is a common source of irritation. An alternative might calculate and keep all palette views, but the fourfold increase of input data overrhead would make a 520's ramdisks tediously small. ________K E Y M A P _______________________________________________________ 1 2 Tst 4 5 6 Sid 8 9 xfm - = ` HELP List ( ) Keep Quit W E Rst Typ Y U Ins Out P [ ] List ^ List Increm. Keep | | Alt Sav Dit F Gr Hf J Kp Ld view \ Palette Keys Increm. Keep | | Zro mez C V B Ng Mg , . /| | Increm. | | spacebar | | xform . view LOOKER attempts to combine both mnemonic representation -- [H] for halftone -- with a cursor pad 'home' position. What this means is that your left hand gets to hunt and peck command keys and your right will stay on the cursor pad. Thus, [cr] -- use your thumb -- flips between the main and work screen and [0] -- use your little finger -- forces the transform. The KEEP buffer keys, [/,*,-,+], are modestly inconvenient on purpose. ________F I L E ___________________________________________________________ LOOKER's file handling is simple in extreme. Either command prompts you for a file name and then tries it. If LOOKER thinks it has an error it will tell you. LOOKER has no directory command, so write down filenames before you fire it up. In any case, LOOKER is so small, QUITing to the Desktop is often the fastest memory aid. LOOKER uses the filename's extension to find the appropriate routine. L LOAD filename.PI1 image file to source image buffer. A low resolution image file stays resident until you load another or cover it with the test pattern (# command). filename.PI3 image file to the WORK screen. A high resolution image file may be loaded directly into the WORK buffer. It is temporary -- you must either move it to to the KEEP buffer or take care not to invoke any command that changes the WORK buffer. Useful to load in area masks that you have created with DEGAS or whatever. filename.DTH file to Dither tables. Loads a previously created custom dither table. Also if you have tried out INSTALL and hashed up the standard patterns, you may load LOOKER.DTH to restore them. S SAVE .PI3 image file from KEEP buffer. This is a standard high resolution DEGAS file. .DTH dither table file. ________P A L E T T E _____________________________________________________ After loading a .PI1 file, LOOKER creates a palette table (displayed on the MAIN screen) by converting each color's red-green-blue settings into a single number between 0 (white) and 3F (black). This derived value may be freely changed, so that user may adjust the new monochrome image to the best possible compromise. All palette commands may be invoked from either the WORK or MAIN screen, and none change the WORK screen's current display. [Up] The palette value is SELECTED by moving the cursor up and down [Down] the Palette table. If the MAIN screen is current, you will see the cursor move and the MICRO screen change. The dark parts of the MICRO screen are those parts of the source that contain the current palette. (A white palette entry will look like a negative of the image. See [N].) [Left] The left cursor key will REDUCE the selected palette value. [Right] The right cursor key will INCREASE the palette value. [1-9] Number keys will set the adjusting INCREMENT. Additionally, HALFTONE will set it to 11. Just reset it as needed. C COPY the WORK buffer's settings to the Alternate settings. This command also copies the current transformation mode. N Often colors are really highlights. Sometimes it is useful to view them as NEGATIVE. This command only changes the MICRO screen's view of the palette entry, not the transformed result. Once made NEGATIVE, you may do as you please. When you return to the palette entry again the display will remember. To remove the NEGATIVE, press [N] again while the proper entry is current. O You may OUTLINE the MICRO screen. This is merely a fallout of internal routines, but what the hell. R After fiddling with the palette for a while, the source values can get quite shuffled -- light is dark, dark is plaid, etc. You may RESET them at any time. Z To isolate a single palette entry, you may ZERO the rest. The cur- rent palette entry will remain unchanged. To zero that one as well, move to another and ZERO again. A powerful feature of LOOKER lets you change several palette values while keeping their relations to each other intact. A PALETTE LIST will change in concert; that is, adjust one by five and all change by five. A list is signified by a CHECKMARK on the palette table. Unlisted values work as before and do not alter the list or the list's settings. Insert ADD the current palette entry to the list. If there is no list, one will be created. ClrHome START a palette list. If there is already a list, it is discarded. Undo DISCARD a palette list. You may change values individually again. ________W O R K B U F F E R & S C R E E N ___________________________ Any valid command may be pressed while the WORK screen is 'current'. If the command requires additional information the MAIN screen is forced current. An invalid key also forces the MAIN screen and leaves the keystroke reminder. [cr] [cr] is a simple toggle to view the WORK buffer. No changes are made to the WORK buffer. A The WORK buffer's settings are saved and the ALTERNATE settings are used to transform the WORK screen. D Makes DITHER the current transformation method and the source image is transformed through a DITHERed halftone, adjusted by the Palette table settings. The pattern selection is unchanged (see T). G Makes GRAY the current transformation method. Any palette entry that is not zero will be forced near middle gray. This transformation is low contrast; only extremes of light and dark will be discerned. GRAY is close to the Desktop's gray but has an entirely different texture. When used in concert with the KEEP buffer, images can be constructed by adding darks and clearing highlights. This is LOOKER's slowest transformation. H A five step HALFTONE is made current and the WORK screen is trans- formed. This is the fastest transformation. (Side effect: the palette increment is set to 11. Thus the right/left keys will go from black to white in five steps.) T TRADE DITHERing pattern for the next in the series of eight, making the new pattern current and transforms the WORK screen. 1) rectangular halftone. 2) clustering halftone. 3) vertical. 4) horizontal fine. 5) crosshatching. 6) diagonal. 7) diagonal. 8) "TV" -- horizontal coarse. X Make MEZZOTINT the current transformation and performs operation on WORK screen. This method reduces image clarity and is slower than Dithering. The mnemonic, by the way, is XOR in reference to the machine language technique used. Sorry. 0 TRANSFORM the WORK screen using the current settings. ________K E E P B U F F E R & S C R E E N ___________________________ LOOKER's output image is built in the KEEP buffer. There is no automatic creation -- you must choose the pieces and add them. The two commands that do this, [+] and [-], change the WORK buffer first. If the next command is STRIKE [/], the KEEP buffer will not be changed. The WORK screen won't be restored after the STRIKE, facilitating comparisons. K You can take a look at the KEEP buffer by pressing [K]. If you haven't kept anything, all you will see is a blank screen. LOOKER then waits for any keypress and then returns you to the previous screen. ( MAIN > KEEP > MAIN or WORK > KEEP > WORK) Since LOOKER doesn't label the WORK and KEEP screens, sometimes you may be con- fused. Just tap the space bar two or three times, until the MAIN screen returns. * ERASEs the KEEP buffer. LOOKER forces the main screen current and asks you if you're sure. Pressing [cr or Y] will ERASE, anything else doesn't. [*] isn't much of a mnemonic, but it does line nicely on the keypad with the next two commands. / STRIKE [/] lets you try out an ADD or SUBTRACT without making a change to the KEEP buffer. [/] must be the very next command after [+] or [-]. Anything else means that you like the results and the KEEP buffer will be changed accordingly. + The next two build the image. ADD sets on the black pixels in the image. It copies all of the on pixels in the KEEP buffer to the WORK buffer. The logical operation is an OR. Thus, if there is anything in the KEEP buffer [+] will ADD to it. - [-] performs a logical AND of the WORK buffer, in effect, copying the white portions of the KEEP buffer. Think of it as SUBTRACTing, but be mindful that you are just cleaning up the whites. However, if you SUBTRACT a light image from very dark image, the effect will approach a straight copy of the light image. Here's a classic bit manipulation table: [+] WORK 0 1 [-] WORK 0 1 _________________ _________________ KEEP 0 | 0 1 KEEP 0 | 0 0 1 | 1 1 1 | 0 1 | results | results The WORK buffer is the one that is really changed at first. If the next keypress is not [/] then the KEEP buffer is updated. To restore the WORK buffer, just press [0]. The KEEP buffer, on the other hand, isn't so flexible. If you change it, it stays changed. Of course, you may ERASE it as often as you like; but recreating the old version can get problematic. Consider changes carefully and like an adventure game, when in doubt, SAVE. ________S Y S T E M ________________________________________________________ # Loads a TEST pattern into the input file buffer. [Help] Shows a command summary on the MAIN screen which is forced current. I INSTALL or alter the DITHER halftone tables. INSTALL maintains its own menu of commands, explained below. Q QUIT is safeguarded: you must reply [y] to exit LOOKER. If you discover another way out while the Main screen is not current, you will not see the Desktop. That is, you will have to reboot. M MAGNIFY shows a 2x view of the Work screen. The cursor pad controls the image and a ghost box helps orient you. Press any key other than the cursor controls to escape. V Prints the current version number of LOOKER, my address for bug reports and 'donations'. & If you have a mind to check how LOOKER works, this version includes a prompted ILLEGAL. Immediately trailing the ILLEGAL is a branch to the top of the menu. If you have neglected to run LOOKER from a debugger, a smallish row of bombs will speed you to the desktop. ________I N S T A L L _____________________________________________________ A single source pixel corresponds to four destination pixels. Taken by themselves, these four can create a five-level halftone. But by applying the source to a larger pattern more levels can be attained. LOOKER uses an array of values ranging from 0 to 63. Each value in this Dither table corresponds to a destination pixel in an 8x8 block of pixels. The blocks are mapped to the screen as 50 rows of 80 blocks. A 64 level halftone is produced by assuming a direct relation between a source pixel's palette entry, table value and location. Different patterns may be introduced to the source image by variously arranging the values in the Dither (threshold) table. INSTALL lets you tailor any of LOOKER's eight tables. The screen shows you the dither table as a grid of numbers, the AUTO-SET value, and three visual displays -- the complete halftone rainbow and two single-value squares magnified 2x. These squares show you what the halftone would look like if all of the source pixels were the same value. You may set this value as you like, using the V command. The keyboard is remapped, so the minimal command set is printed as well. R RETURN to the LOOKER environment. [cr] Select table to change. [arrows] SELECT the value to change. The table wraps both vertically and horizontally. [##] CHANGE value. For single digit values, you may either use a leading 0 or any non-numerical key to signify "that's all". Notice that when the value is accepted, the cursor advances to the field to the right. F[##] FILL the dither table with a single value. V[##] Set the VIEW threshold. U UPDATE moves the changes to memory. A 64 level halftone contains the values 0 to 63 with no repeats. Manually entering the sequence is a hassle, so several commands are provided to facilitate entry. With exception of the first, all are on the cursor keypad. A[##] Set AUTO-INCREMENT value. A [cr] starts from zero. [Help, Undo] Copy the AUTO value to the current cursor position. [Clr Home] Change the value located by the cursor to the current AUTO value then INCREMENT the AUTO value. [Help] Change the value located by the cursor to the current AUTO value then DECREMENT the AUTO value. Here's a sample pattern that abandons the halftone concept. 8 32 7 32 6 32 5 32 32 0 32 7 32 0 32 5 0 48 0 0 0 48 0 32 0 63 48 63 48 63 0 6 0 48 0 48 0 48 0 32 0 63 48 0 48 63 0 7 7 0 63 0 63 0 8 32 32 7 0 0 0 5 32 8 Please note: Work out your pattern on paper first. Although INSTALL is somewhat interactive, it is more suited to rapidly reconfiguring a table that has already been worked out. In designing it, give thought to the derivative patterns created by adjacent blocks. Lastly, INSTALL is more or less slapped together; for its rough spots, I apologize. _______F O O D f o r T H O U G H T___________________________________ The basis of LOOKER's transformations is the source image's palette. The monochrome replica of the source image is an interpretation of its hue and saturation. Photographers are familiar with the distinct differences be- tween the skills required for color work and those for black and white. Often an image that 'works' in one form suffers when translated. On the other hand, many images can be strengthened by judicious emphasizing. Try XEROXing several photographs. Try to pick a photograph that won't work and one that will. If you can fiddle with the machine's controls, do so. Turn off the color on your TV. News shows often look good in either mode. Color movies and series often lose something. "There's no substitute for experience": Buy a roll of black and white film and shoot it up. Do some fast drawings with one crayon. Then do some with sixteen. Run LOOKER at every PI1 file you can get your hands on. A monochrome user's biggest surprise is how mediocre many public domain images really are -- this emperor often has no clothes. Your run-of-the-mill color slide has about fifty visible levels of tone. So does a black and white negative. Modern photographic papers compress this scale, yeilding ten different tones in a photograph. Photographic negatives have remarkable resolution. Consider a family reunion and its mandatory line-em-up-and-smile. Even the cheapest camera results in recognizable renderings, even when enlarged 20 times or more. Photographs in the daily paper usually use 85 dots per inch. Each of these dots vary in size, typically labeled 10%, 20% and so on to 100%. Newsprint is not the best material on which to print ink, thus only six or seven steps are actually distinguishable. However those 85 dots per inch on newsprint can readily exceed the capacity of the ST's screen. Let's compare 50% grays: 640 pixels in row with half on, half off equal about 3 3/4 inches of newspaper. The 400 vertical dots are about 2 1/4 inches. Now vary the newsprint's gray down to 10% and up to 90%. The printed dot gets smaller or bigger. Not so with the computer screen. One has to clear more pixels or darken more pixels. So, as we lighten and darken, the computer screen loses resolution. A guesstimate: a dithered LOOKER image is comparable to 1" x 3/4" high of newspaper. Something to try: cut a 1" x 3/4" hole in an index card and hunt through the newspaper for interesting images. ________M I S C E L L A N Y______________________________________________ Files in this release include: LOOKER.PRG, LOOKER.DOC, LOOKER.DTH. LOOKER is shareware. What I would like you to do is to put a real dollar bill in a envelope and mail it to me. Put your return address on the envelope. I will put the dollar in my wallet and the envelope in a safe place. Individuals may obtain LOOKER's source code (Alcyon AS68) by sending $10, a disk and a return mailer. Commercial enterprises are welcome to make me an offer I can't refuse. LOOKER is a live program, that is "not done". I will cheerfully correspond to anyone about LOOKER, its use, its documentation, its future and what a crummy user interface it has. Write! Bibliography: Atari ST Internals by K. Gerits, L. Englisch, R. Bruckmann (Abacus) Hitchhiker's Guide to BIOS (Atari developer's kit) Tip: use a black magic marker to block out the cute shit in the LINE-A 'documentation'. Computer Graphics by Donald Hearn/ M.Pauline Baker (Prentice Hall) Programming the 68000 by Steve Williams (Sybex) Crappy binding, mathematics nonexistent. [Rule of thumb for judging 68k AL books: multiplication and division routines for 32 and 64 bit values. Most fail.] Solid Shape Drawing on the Commodore 64 by Richard Rylander (Dr. Dobb's Journal, May 1985) Sets out the underpinnings to dithered halftones and other marvels. This is a great article. GRAFCON ST by Patrick Bass (Antic, July 1986) A Digital Dissolve for Bit-Mapped Graphics Screens by Mike Morton (Dr. Dobb's Journal, November 1986) Frederick Hawkins ~ 1020 N. 6th Street ~ Allentown, Penna 18102 July 31, 1987 ________G L O S S A R Y__________________________________________________ author One Frederick Hawkins, BFA/MFA in Printmaking from the San Francisco Art Institute, whose obsession with computers has prevented him from driving a cab. Still looking for the ideal hakker's job. Credentials: none. Demerits: likes FORTH, hates MODULA2, PASCAL, and C; writes only assembly with com- ments. buffer A block of memory set aside for a particular purpose. LOOKER has a WORK buffer, a KEEP buffer, two small window buffers and an INFILE buffer. Each buffer consists of the image data and some additional information. color A set of points in the source image that are all alike. LOOKER doesn't change the color;; it changes how the color is represented. This is the absolute bones of an image. dither A technique whereby a destination pixel is set or not, depending upon the value assigned to its corresponding source pixel and a threshold value. In LOOKER, the screen is cut up into 8 by 8 blocks of 64 pixels, eash assigned a number from 0 to 63. This number is a threshold and the block is called the threshold table. If the source pixel's color is darker than the threshold, the destination pixel is set. By variously arranging these threshold tables, different halftone patterns are possible. DTH The semi-obligatory extension. This is LOOKER's, indicating the saved dither tables. DTH files are made of 8 tables of 64 bytes. The tables are not demarked in any way except by length. halftone A method of simulating a gray by interspersing white and black dots. Halftones are always patterned. image A short word for picture. KEEP The buffer and screen that is used to assemble LOOKER's output. list A linked set of colors that may be adjusted in concert. MAIN The usual desktop screen where text is printed in LOOKER. mezzotint A random patterning that simulates an etcher's technique. This is a low resolution transformation because the random- ness adds noise to the image. MICRO A quarter-size window used to show the palette and magnified views. onebuck A token of your esteem, which, in quantity, may pay for the disks used in creating LOOKER. palette In general, a set of sixteen colors that comprise a low resolution image. In LOOKER, these colors are converted to a gray level, ranging from 0 to 63 (white to black). resolution Nominally, this is the sharpness or clarity of an image. ST usage is based on the number of pixels in a given type of image. Low resolution is made up of 200 rows of 320 points, medium resolution has 200 rows of 640 points, and high has 400 rows of 640 points. LOOKER maps a single low rez pixel onto a 2 by 2 dot of four pixels. screen The part of a buffer shown to the user and variously changed by LOOKER's commands. settings The gray level assigned to a palette color. Sometimes refers as well to current transform (dithering, mezzotint et al) as well. shareware A poor man's justification for spending so much time. WORK A temporary screen buffer. It must be moved to the KEEP buffer to be saved.