Are there any image editing or research tools, commercial or otherwise which will allow me to:

  • map colors (images) from 16-bit RGB (565) space to 24-bit RGB (888) space or vice versa
  • save files in PNG, GIF, or JPEG
  • give user the ability to control how colors are mapped from 16-bit space to 24-bit space.

Here's a little background for this request.

I'm working on a project evaluating an LCD display panel. The native bit depth of the panel is 24-bits (RGB 888) and it is currently available on an evaluation kit that uses an LCD controller that supports 24-bit output only.

The LCD controller on the product for which this panel is being evaluated only supports 16-bit output (RGB 565). In the final design the remaining bits for each color channel on the panel will be connected in some way.

The evaluation kit does not take RGB inputs (as mentioned above it only takes PNG, JPEG, or GIF). I'm looking for a way to create 16-bit and 24-bit RGB files which will then be converted to a PNG. By manipulating the values of the R, G and B channels in the source files (16-bit and 24-bit) I want to compare the difference between driving a 24-bit display with 24-bits of color and 16-bits of color (extended to 24-bits).

I'd also be interested in learning about others experiences with this sort of evaluation and the sanity of my proposed test methodology.


1 Answer 1


I don't think you'll be able to accurately mimic the 16bit display without knowing more about the dithering method it uses. Some 16bit and 18bit displays animate their dither pattern, meaning they actually look better than you may expect (I believe lots of laptop displays use 18bit with an animated dither).

Also, there's quite a few dithering methods (patterned, stochastic etc), with a big range of results.

Photoshop's indexed colour mode converts to index colour (of course!), but it tops out at 256 colours, so it doesn't do what you're after.

If you save an image as a BMP from Photoshop, you are given the option to save as 16bit with the R5 G6 B5 mode (click Advanced Modes when saving). If you want to convert that image back to 24bit, simply open it again in Photoshop. The image won't gain any quality back, but I assume that's what you're after.

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  • @dinesh: Marc makes a good point about animated dithering. You will need to check the monitors for this, or if it has Frame rate control which is the technical name for this. If the monitor applies FRC (which is a cyclic dithering) you won't be able to see the actual raw 16-bit data converted without dithering to 24-bit.
    – user7179
    Nov 13, 2012 at 0:27
  • @Marc Edwards: Thanks for the explanation. I was able to run the tests that I needed to evaluate my display with the info you provided. I need to read up on dithering but as far I can see the difference between 16bpp and 24bpp on a 24-bit panel is minute.
    – dinesh
    Nov 13, 2012 at 8:24
  • @Abdias Software: Thanks for your comment. In my case I'll be able to control the dithering that is applied to the lower bits of the color channels. Even so it doesn't look like there's any appreciable difference between the two cases.
    – dinesh
    Nov 13, 2012 at 8:27
  • For the benefit of other readers, Photoshop allows you to save a file as bmp only if the file is opened in Image -> Mode -> RGB color and Image -> Mode -8Bits/Channel
    – dinesh
    Nov 13, 2012 at 8:32

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