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A program to display images saved as GIF files on an IBM PC Hercules
graphic card. The program operates as follows:
Read GIF file header and determine size of the image.
Dynamically allocate enough memory to hold all the image internally.
One byte per pixel is always allocated, so a little bit more than
width*height (of screen, not image) bytes are required.
Reads the image in. Interlaced images are read correctly, although
they are displayed sequentially.
Display first image using the defaults as set by the command line option.
Goes to interactive mode. For full description of the interactive mode
gif2herc [-q] [-d dither] [-z zoom] [-t bw] [-m map] [-i] [-b] [-h] gif-file
If no gif-file is given, gif2herc will try to read a GIF file from stdin.
Quiet mode. Defaults off on MSDOS, on under UNIX. Controls printout
of running scan lines. Use -q- to invert.
Sets size of dithering matrix, where dither can be
2,3 or 4 only (for 2x2, 3x3 and 4x4 dithering matrices). Default is 2.
Note: the image will be dithered only if the mapping (see -m)
selected dithering mode.
Sets zoom factor of the image. Zoom factor should be
power of 2 up to 256. Default is 1 (no zoom).
Sets threshold level for B&W mapping in percent.
This threshold level is used in the different mappings as selected via -m.
Default is 19%.
Select method to map colors to B&W. Mapping can be:
Default is option 0, which is much faster than the other two.
Every non-background color is considered foreground (white).
0.3 * RED + 0.59 * GREEN + 0.11 * YELLOW > BWThreshold is considered white.
Colors are mapped as in 1, and use dithering of size as defined using
-d option. BWthreshold is used here as scaler.
Invert the image, i.e. black -> white, white -> black.
Disable beeps. Every time the image is complete, or a wrong key was
presses, sound is generated. The -b option disables that.
Print one line of command line help, similar to Usage above.
Once the image is displayed, the program goes into an interactive mode
which recognizes the following commands:
- C - get Color and position
- In this submenu, a cursor appears and the location and color of the
pixel underneath it are printed. The 4 arrows may be used (shifted for
faster movement) to move the cursor. Any other key will abort this
- D - zoom Down
- Zoom down by factor of 2 unless current zoom factor is 1.
- H - Increase dither matrix size
- ...unless current size is maximum (4), in which case size is set
to minimum (2).
- I - Invert
- Invert the image, i.e. white -> black, black -> white.
- M - Method
- Increment color -> BW mapping method, unless current method is maximum
(2), in which case method is set to minimum (0).
- R - Redraw
- Redraw the image.
- S - print Status
- Print status of image and program.
- U - zoom Up
- Zoom up by factor of 2 unless current zoom factor is 256.
- arrow keys
- The 4 arrow keys can be used to pan in the desired direction, if the image
overflows in that direction. If the image fits into the screen, arrow
keys are ignored. The panning steps are 1/2 screen if not on image end.
- SPC - abort
- Space bar may be used to abort current image drawing.
- ESC - abort
- Escape may be used to abort current image drawing.
Eric S. Raymond <email@example.com>