Photoshop plugin to create convert 8,8,8 color images to 6,6,6 color with dithering

[aryaabraham]

I need to generate images for a mobile device which only support 64 R, 64 G and 64 B levels. A long monochromatic gradient that looks good on my computer monitor shows up with bands on the device since the display can only support a quarter of the colors that a regular display can.

Is there a way to convert a 24-bit (8 R, 8 G, 8 B) color image into an 18-bit color (6 R, 6 G, 6 B) image with dithering. I have used the mode change to create images with a 256 color palette. That does not help me because I have more than 256 color to work with.

Is there anybody who has worked with mobile devices that can give me some pointers on how to covert my images so they will look good on a mobile screen with a lower color depth 6 bits/color instead of 8 bits/color?

Thank you
Arya

[Tron]

Sorry I don't really know the answer to this, but I do know 18-bit is not standard.

[aryaabraham]

Tron,

We have an option of running the screen in 5,6,5 color mode (16-bit RGB). Is that a standard format and do you know whether there is a plugin at that color depth for removing bands from slow gradients?

Sincerely
Arya

[Tron]

Yes... 8, 16, or 32-bit depth is standard. I don't know if Photoshop supports anything else actually.

Maybe if you post one of the images and let us know the desired output specs we can help you more.

How many of these images are we talking about? If it's just a few you may have better luck just remaking the gradients in a lower bit depth mode.

[aryaabraham]

Tron,

Thank you for offering to help. Since I need to create many images in this fashion, I will have to learn how to do this from you.

First, let me try generating a gradient at a lower color depth as you have suggested. If that works, I shall post the solution to this group. If it does not, I shall post the most troublesome image to see if you can help me find a solution. I don't have Photoshop at home so I shall try this at work tomorrow.

Sincerely
Arya

[Gaussian]

If you can figure out a method that works, you can easily create a Photoshop Action to apply the process to a large number of images very quickly. Photoshop has excellent automation tools

[aryaabraham]

While testing out the dithering gradient operation in Photoshop/GIMP, I noticed that both software packages could display a 24-bit/32-bit image on a 16-bit display color display without banding. I trudged through the GIMP source code to find the algorithm they used and incorporated it into my own program.

I have posted my software (LoRes) online so anybody else on this helpful group who needs it can get to it.

Arya