Venu image import distorts BOTH in simulator and on device.

Long story...

The venu device does indeed support 16-bit color, which doesn't normally use dithering. Unfortunately the venu has such a large screen, a full-screen bitmap without any transparency requires 304KB of memory, even if you only use a few colors. Someone decided that it would be a good idea to automatically reduce the number of colors in the image when compiling.. to reduce the required memory. A full-screen image with 4 or less colors would take 38KB. But once you reduce an image down to a smaller color set, you often need to apply dithering to keep it looking decent.

If you don't mind using all of the memory on the image, you can set automaticPalette="false" in the bitmap element in your resource file. As you've discovered, you can set dithering="none" to disable dithering, and you can explicitly set a color palette using the <palette /> element.

You’re right, a very good article. 

One question is why dithering even affects Venu with a range of colours that should be able to handle pure red, green, blue. So error should consistently be zero. 

I’m guessing dithering goes to a much smaller range of colours than Venu supports?

This is indeed an artifact of the dithering algorithm that we are using (Floyd-Steinberg). You can avoid this by disabling dithering. Of course we could provide a few more options for dithering algorithms.

This is an interesting article describing several different dithering techniques:

tannerhelland.com/.../dithering-eleven-algorithms-source-code.html

Hi, a ticket has been created and we are looking into this. 

OK, it looks like this is specifically a bug with dithering.

If I set dithering="none" in the resource file, the bug disappears.