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HamLab Version 1.1 (c) Copyright 1990, 1991 J. Edward Hanway All rights reserved. OVERVIEW The purpose of HamLab is to read "foreign" images, especially those created for high-resolution, deep-bitmap displays, and convert them to Amiga Hold-and-Modify (HAM) and Sliced-HAM images, while trying to preserve as much of the original's quality as possible. The HAM and SHAM images can be displayed (on a large "virtual screen" if necessary) and saved as IFF files, suitable for use with a HAM paint program like NewTek's DigiPaint. Currently, HamLab understands the following formats: GIF, TIFF, Spectrum 512, MTV, QRT, DKBTrace, PBMPLUS, Sun Rasters HamLab should work on images up to about 1500 pixels wide and any height, although you will probably need a 1M Agnus chip to display images more than 1008 pixels wide. HamLab has been tested with 1152 x 900 and similar images. SYSTEM REQUIREMENTS REQUIRED AmigaDOS 1.3 and ARP 1.3 (only the 17100 byte LIBS:arp.library file is required) *OR* AmigaDOS 2.x RECOMMENDED PIPE: device (comes with AmigaDOS; needed only if the "Use Pipes" option is used) HamLab runs on a 68000, a 68030, and everything in between. At least one megabyte of memory is recommended. (That should be enough to work with 640 x 480 images when the "Use Pipes" option is used.) INTRODUCTION To use HamLab effectively, it helps to understand the basic idea of what it's doing behind the scenes. The complete conversion process looks like this: Original image | | filtering v 24-bit image | | scaling, color mapping, then quantizing | (with optional dithering) v 12-bit (4096-color) image | | cropping, then analysis v 12-bit image + 16-color palette | | display or save v cropped HAM image In the first step, called filtering, the original image is decoded and the image data is saved in a temporary 24-bit RGB file. This is the only step where the original image format (GIF, TIFF, etc.) matters. In the next step, several things happen. First, the image is resized, then the color of each pixel is remapped using the color response curves (this allows adjustments for brightness, contrast, etc.), then the 24-bit RGB data is crammed into the 4096-color palette of the Amiga, optionally using dithering. The 4096-color image is then cropped, then HamLab analyzes the remaining area to select 16 color registers that will minimize the "fringing" associated with Hold-And-Modify mode. Once the 16 color registers have been selected, the 4096 color picture can be displayed or saved in HAM mode. COMMANDS OPEN (shortcut: 'o') This command brings up a file requester and allows you to open a new image file. HamLab tries to identify the file according to its configuration information, and if it can be identified, the appropriate input filter will be run and the image will be converted to a 24-bit RGB temporary file. If the "Use Pipes" option is selected, then a temporary file won't be created. Instead, a pipe will be opened and part of what is normally the ANALYZE command will be executed using the data coming through the pipe. See below for more information on using pipes. ANALYZE (shortcut: 'a') This command reads the 24-bit temporary file and does the necessary calculations (called quantizing) to fit it to the Amiga's 4096 color palette, then picks 16 colors to use in HAM mode to minimize HAM fringing artifacts (analyzing). Depending on how you set the "Cache12Bit" option in the configuration file (see below) the resulting picture will either be held in RAM or in another temporary file. Color correction and scaling are also done in the quantizing step. DISPLAY (shortcut: 'd') This command opens an intuition HAM or SHAM screen and renders the picture into it. If your Workbench screen is overscanned, this screen will be overscanned, too. If the image that you're converting is larger than the screen size, then you can pan around the image using the arrow keys or by holding down the left mouse button and dragging. The right mouse button or space bar will close the display screen. (Other shortcut keys still work, too.) SHAM screens are limited to 320 pixels wide (any wider and the Amiga Copper doesn't have time to load a new palette for each line.) You can still pan SHAM screens, although panning, especially vertically, will be very sluggish compared to a HAM screen. SAVE (shortcut: 's') This selection brings up a file requester and allows you to save the image as an IFF file. You need not display an image before saving it. REVERT (shortcut: control-R) This button is enabled any time you change a setting that would require you to re-analyze a picture. It will restore all settings to the ones that were used the last time the picture was analyzed. Close Gadget (shortcut: 'q') Clicking the close gadget of the HamLab window exits the program. OPTIONS OUTPUT OPTIONS SHAM (shortcut: 'm') When this option is enabled, HamLab creates a "Sliced-HAM" image rather than a normal HAM image. A SHAM image uses a different palette for every line (every other line for interlaced images). This means that, on some pictures, HamLab can do a much better job of minimizing HAM artifacts. However, SHAM doesn't come without a price. SHAM pictures will show artifacts if they are overscanned horizontally. They are much harder to scroll, and currently no paint program that I know of can work with them. INTERLACE (shortcut: 'i') When this option is enabled, the HAM (or SHAM) image will be interlaced. The image size is not changed. For HAM images, toggling this option does not require any recalculations, and can even be done while the image is being displayed. For SHAM images, the image must be re-analyzed. OTHER OPTIONS USE PIPES (shortcut: 'p') When this option is enabled, the next time you OPEN a file, rather than creating a huge temporary 24 bit RGB file, the image will be piped directly through part of the ANALYZE command using the AmigaDOS PIPE: device. Although this saves a lot of temporary file space and can get the conversion done faster than going to a temporary file, even in RAM:, it does mean that if you need to re-quantize an image (like after you turn dithering on or off), the image must be re-opened and converted from its original format all over again. FIX BACKGROUND (shortcut: 'k') This option causes HamLab to reserve color 0 for the background/ border color, and assign the other 15 to minimize fringing within the picture. Normally, HamLab will assign all 16 colors to minimize fringing, then assign the closest background match to color 0. In SHAM mode, this option has a different meaning. To be compatible with current SHAM viewers, HamLab forces color 0 to be black for SHAM pictures. If this option is turned on, HamLab will use the true background color, instead. After toggling this option, the image must be re-analyzed, but the 24-bit to 12-bit quantization will not be recomputed unless changing one of the other options necessitates it. FREEZE PALETTE (shortcut: 'f') While this option is set, HamLab will keep the current palette and not do any analysis to find a better one. This can be useful if you wish to convert several images using the same palette. Load one, analyze it, and lock the palette for the remaining pictures. This option can also be useful if you want to improve rendering in a portion of the image. Crop out the unimportant parts of the picture, then analyze it. Lock the palette, then restore the cropping area to the full image. FAST ANALYZE (shortcut: 'z') This option affects how HamLab chooses the 16 color palette used to minimize HAM fringing artifacts. When disabled, HamLab analyzes the picture separately for each of the 16 colors, each time picking the one which helps the most. When enabled, HamLab only analyzes the picture once and then picks all 16 colors. Although the slow analysis should, in theory, be better, in practice, I notice little or no difference in quality between the two methods, and the fast analysis is 16 times as fast. After toggling this option, the image must be re-analyzed, but the 24-bit to 12-bit quantization will not be recomputed unless changing one of the other options necessitates it. SCALING OPTIONS HamLab incorporates very fast scaling routines which can resize a 24-bit image to anything from 10 to 1000 percent of its original size. You can enter separate scale values for X and Y directions, and you can specify them either as a percentage of the original size, or as the desired size in pixels. QUICK SELECTION (shortcuts: 'x' 'y') A few commonly used scaling values are built into HamLab as special cases so that they'll run even faster. Clicking on the X or Y letters will cycle between these values, which are: X: 50%, 100% Y: 50%, 100%, 200% CONSTRAIN (shortcut: '=') When the '=' gadget is selected, changing one scale value will automatically change the other proportionally. With the gadget off, you can make changes to one value at a time and correct aspect ratios. When you change scaling values, the image must be re-quantized. NOTE: When you load a new picture, the scaling values will be unchanged. Usually you'll want to have the scaling gadgets in percent mode, or else the picture will be scaled to the same size as the last one. CROPPING OPTIONS Using these options you can throw out all but a portion of the image. You can set the cropping area in three ways: Specify the upper left corner and the size of the cropping area. Specify the upper left corner and the lower right corner. Display the picture, hold down the shift key, then use the left mouse button to select the cropping area. Whenever you change the cropping area, you must re-analyze the image. Since you still have the same number of colors in the palette to minimize fringing, but a smaller area to cover, you can usually get slightly better results on cropped areas than the whole image. FULL IMAGE (shortcut: '#') This button resets the cropping area to include the entire image. COLOR CONTROL OPTIONS HamLab allows you to modify 24-bit RGB data by using each red, gren, or blue value as an index into a lookup table. These tables are shown on the screen as "Color Response Curves." You can manipulate these curves through the Brightness, Contrast, and Gamma controls, or you can use the mouse to draw parts of the curve by hand. RED (shortcut: 'r') GREEN (shortcut: 'g') BLUE (shortcut: 'b') These buttons make the corresponding curves active and inactive so that you can work on them individually or in combination. BRIGHTNESS (shortcuts: '(' ')') Shifts the color response curves up (brighter) and down (dimmer). CONTRAST (shortcuts: '[' ']') Changes the slope of the active color response curves. A steeper curve will result in a more contrasty image. GAMMA (shortcuts: 'c' 'u') (The letters stand for "Compensate" and "Uncompensate.") Gamma refers to the nonlinearity of an real-world device like a monitor. Basically, this means that changing from 0 to 1 may not produce the same change in brightess as going from 14 to 15. Different monitors have different gammas (1.0 is perfectly linear, but most NTSC monitors are more like 2.2), so the same image will look different depending on the monitor. The use of this option depends on the original image. Images created by Amiga programs are likely intended for NTSC or PAL monitors and won't need gamma correction, while VGA GIF images are probably intended for monitors with lower gamma. If you know the gammas of the original image and of your monitor, you can enter the original gamma, hit "Uncompensate," enter the new gamma, and hit "Compensate." Experimentation helps. Gamma correction can have other uses, too. By setting the gamma value to something like 1.1, clicking "Compensate" will gradually bring dark portions of the picture out of the shadows while reducing the contrast of the lighter portions. NEGATE (shortcut: 'n') Inverts all active curves so that the image produced looks like a photographic negative. INIT (shortcut: ',') Resets each curve to a 45-degree line, so that the output exactly matches the input. ONly the active curves are affected. LOAD (shortcut: '.') Brings up a file requester and allows you to load the color response curves. Only the active curves will be loaded. SAVE (shortcut: '/') Brings up a file requester and allows you to save the color response curves. All three curves are always saved. DITHERING OPTIONS Whenever the 24-bit file is squeezed into the Amiga's 12-bit palette, (the quantizing operation) some loss of color accuracy may occur. The fastest way to quantize is to simply pick the closest 12-bit color for each pixel, but for some images this can cause "banding," an artifact where a gradual color change results in several sharp-edged bands of color. (This happens a lot in soft shadows.) Dithering can significantly improve the results when converting images which began life on a system with a larger color palette, such as the 262,144 color palette used by the VGA and the 16.7 million color palette of many 8-bit and 24-bit systems. After changing dithering options, the image must be re-quantized. NONE (shortcut: '0') All dithering is disabled. This is the fastest option. FLOYD-STEINBERG (shortcut: '1') Whenever each pixel is quantized, the resulting error is distributed to four adjacent pixels. In my opinion, this selection is a good tradeoff between computing time and quality. JARVIS (shortcut: '2') Similar to Floyd-Steinberg, except the error is distributed to 12 pixels. Quite slow. STUCKI (shortcut: '3') Very similar to Jarvis and about the same speed. ORDERED (shortcut: '4') Uses fixed patterns to represent intermediate shades. This option is quite fast, but the regular dithering patterns aren't as pleasing as the more irregular patterns produced by Floyd-Steinberg. RANDOM (shortcut: '5') Adds some random noise to the picture while quantizing. This avoids the regular patterns of ordered dithering, but the resulting image can look like a TV with bad reception. About the same speed as ordered dithering. SPIRAL-DOT (shortcut: '6') Similar to ordered dithering, and the same speed, but the patterns used makes it look like you're looking through a screen. This looks better the farther away you get. Seriously. MISCELLANEOUS HamLab and its input filters are "pure" code, so they can be made resident if you so desire. Displaying the picture is the only thing that requires any significant amounts of CHIP RAM. Note that a 640 x 480 HAM image takes about 230K of CHIP ram, though not all contiguous. ACKNOWLEDGEMENTS Thanks to Scott Rider for assistance in debugging and testing, and to everyone who submitted suggestions and comments on the original version.