Say, I have a JPEG photo image with lots of colours. Grayscale or colour one. When I load it on Iliad it looks pretty ugly. Is there a smart color reducing / predithering linux pipeline that image gurus out there could advice? Manual tweaks in gimp are not welcome, but I can do it as a last resort. Can ImageMagick convert(1) be told about what the iliad's palette is?

man ImageMagick :-P

I have to say i never used IM. but this could prove helpful:

-map filename

choose a particular set of colors from this image.

[convert or mogrify].

By default, color reduction chooses an optimal set of colors that best represent the original image. Alternatively, you can choose a particular set of colors from an image file with this option.
Source: http://www.imagemagick.org/script/command-line-options.php

Say, I have a JPEG photo image with lots of colours. Grayscale or colour one. When I load it on Iliad it looks pretty ugly. Is there a smart color reducing / predithering linux pipeline that image gurus out there could advice? Manual tweaks in gimp are not welcome, but I can do it as a last resort. Can ImageMagick convert(1) be told about what the iliad's palette is?I don't know about the quality but sunning convert with the arguments -colorspace GRAY and -colors 16 as arguments should do it.

don't know about the quality but sunning convert with the arguments -colorspace GRAY and -colors 16

-colors 16

reduces the palette to <= 16 colors, but not necessarily THE 16 colors available on iliad! the -map option advised by b_k was what I initially thought of myself, but it requires an image with a correct palette in it to start with as a map.

so whats the problem? ask iRex for a BMP. I would think they have one.

so I guess I am asking them and anyone else who's got it set up already...

OTOH, you could try to create a palette by yourself with GIMP. The supported colors are mentioned in the "How to create content ..." document from iRex.

I'm attaching the pinlock file included in the ipdf sources. If you have imagemagick installed on your computer, you should be able to use the following command to convert it to a color map that best matches the iLiad.

convert -dither -map pincode_lock_background.png original_image.jpg updated_image.jpg

Thanks for posting the PNG. Unfortunately, neither your command line, nor the same with the addition of -colorspace GRAY -colors 16 improved anything with my photo :( The resulting picture looks great on my PC display, yet looks ugly, with visible added edges at color boundaries, on the iliad. Dithering doesn't seem to visibly help a lot...