16-bit colour representation
steve at holdenweb.com
Wed Jul 25 18:18:22 CEST 2007
Diez B. Roggisch wrote:
> beertje wrote:
>> This has me a bit stumped...
>> I'm trying to extract pictures from a file. So far I'm successfully
>> retrieved the header and what I think is the colour for each pixel.
>> Here's the description:
>> 3) The picture data format:
>> The color information is 15 bit data stored in 16 bit. This means the
>> significant bit is unused. The data is stored line for line in little
>> endian Intel format starting with top left edge to bottom right edge.
>> is normally called chunky format.
>> Bit 0.. 4 blue value
>> Bit 5.. 9 green value
>> Bit 10..14 red value
>> So I've got a list of 16-bit numbers, but how to extract RGB info from
>> those I'm a bit lost. I thought at first I should convert the decimal
>> (say 23294) into a binary (say 0101101011111110) into something like
>> blue: 01011
>> green: 01011
>> red: 11111
>> But encountered two problems: First, I don't know what the best way is
>> to do this conversion, but more importantly I don't see how every
>> colour could possibly be represented like this. 65535 is presumably
>> white, but converting this into chunks of 5 gives me a 31, 31, 31, a
>> dark shade of grey.
>> I guess I'm on the wrong track completely?
>> I'm a bit unsure about how to treat what the guide calls 'UWORD'...
> ANDing and SHIFTing are your friends here:
> v = 0x0bcd
> b = v & 0xf
> v >>= 4
> g = v & 0xf
> v >>= 4
> r = v & 0xf
> print r, g, b
Alternatively, using 5-bit colors you would use
b = v & 0x1f
g = (v >> 5) & 0x1f
r = (v >> 10) & 0x1f
Steve Holden +1 571 484 6266 +1 800 494 3119
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