How to optimize images for 256 color versions of PCD7.D4xx MB panels

FAQ #100979

 

The 256 color versions of PCD7.D4xx MB panels can display a well defined palette of RGB colors. The gif files used as images in the S-Web-Editor can as well contain up to 256 colors, but they are most of the time optimized according to the colors that are present in the image, which do usually not match with the colors of the PCD7.D4xx palette.

If you use unoptimized images, the panel chooses for each pixel the color that matches best, but the result can be suboptimal. This FAQ proposes a procedure that allows to improve the results using the PC based image processing software photoshop or the freeware alternative gimp. The FAQ assumes that you have one of them available and know how to use it.

There are three advantages when converting the images on the PC instead of leaving the color conversion to the panel:

• you can preview and optimize the result (playing with the dithering, contrast or what ever properties according to the image to convert)
• thanks to dithering the conversion is not oriented to single pixels but to larger parts of the image. This is particularly advantageous for images that contain a lot of similar colors like images of metal machine parts for instance
• a far better result in most of the cases

Suggested procedure

1. Getting the right sources
   Best results are acheived using image files with a sufficient number of colors, which means usually jpg, png, psd or tiff files.
   
2. Resize the image to the required dimensions
   Avoid making images bigger, the results are most of the time not satisfactory.
   
3. Change the color mode to indexed (custom)
   Attached to this FAQ you can find a color table for photoshop (.act) and another one for gimp (.gpl). These files contain a definition of the 256 RGB colors the PCD7.D4xx 256 color panels can display.
   
   To make the color palettes available in photoshop: 
   Copy the act file to any place on your computer that you remember when you have to choose a custom color palette
   
   To make the color palette avaiable in gimp:
   Copy the .gpl file to the palettes folder, example for gimp 2.0: c:\program files\gimp-2.0\share\gimp\2.0\palettes
   The path will depend on the program and language versions, so you might have to search for .gpl files to find the right location. The SBC color palette is available at the next start of gimp
    
4. Store the image as gif file
   
   Gimp
   Save as... 
   
   Photoshop
   Do not use Image Ready (CS, CS2) or the Store for Web... feature (CS3 +) of photoshop like you would usually do to create images for the web! These wizards suggest per default other color palettes and it is easy to make errors that make you loose the improvements of this procedure. Use Save As with file type gif instead.
   
5. Use the images in your S-Web-Editor project
   Same procedure as usual.