You keep saying 16-bit, but there is no way my computer can produce a 16-bit color image. Even when I download the "bye.BMP" that was posted here, it still says 24-bit.
In Corel Photo-paint 11 under Windows XP, the only 16 bit option is a "16-bit greyscale".
Even when I click properties on the image in Windows Explorer, the file manager summery says that the image is 24-bit color.
When I add my own custom 24-bit BMPs to a firmware, it flashes fine.
In Photoshop and many good graphics applications you can save as 16-bit. BMP can be saved as 16, 24, and 32-bit.http://paulbourke.net/dataformats/bitmaps/
As you will see on this page,
16 bit RGB
This is generally a direct system with 5 bits per colour component and a 1 bit alpha channel.
Throughout the firmware (for menu resources/backgrounds) you can use 24-bit PNG with alpha-transparancy (nice smooth see-through bits, with anti-aliased edges). For some parts of the firmware, such as the folder/filetype icons, you need to use 8-bit PNG with a #ff00ff mask where you want them to be see-through (this isn't smooth, and has blocky edges).
From my experience the bootscreen/shutdown screen have had to always be 16-bit BMP. This could be a filesize limitation rather than a palette limitation, but either way, the 16-bit is going to be a smaller filesize, so if you can do it that way it is a good idea.
There are some examples of different bit-depth BMPs on this page - http://wvnvms.wvnet.edu/vmswww/bmp.html
You should be able to notice the difference between the 16-bit and 24-bit BMP examples, most notably in the white>black gradient.
MSPaint adds to the confusion about bit-depth because it uses a stupid naming convention for the types of BMP you can make:
Monochrome Bitmap = 1-bit
16 Color Bitmap = 4-bit
256 Color Bitmap = 8-bit
24-bit Bitmap = 24-bit
And then ofcourse you have the largely compressed JPEG on MSPaint which is no good for anything, and the largely under-compressed raw 24-bit PNG on MSPaint which produces files too large to be used practically.
So there you go, a computer can produce a 16-bit color BMP image, you just need the correct software for it. I personally use Adobe Photoshop CS3.
A free alternative to Photoshop would be The Gimp
, which lets you save 16-bit BMP files just fine. Don't be confused by the number of 16-bit options it gives you, the one we're interested in is the 16-bit RGB 565 option, which is the standard 16-bit.
When choosing to save a file as BMP in The Gimp, just click the little 'Advanced Options' toggle, and you will be able to pick the correct bit depth.
It's all too easy to forget that 15 years ago, our computers used to have 2MB onboard video and could output at a maximum of 1024x768@16bit "High color"!