[maemo-developers] [maemo-developers] Nokia SDL color format for pixels

[From: Joni Valtanen]

On Thu, 28 Aug 2008, Michael Stepanov wrote:

> On Tue, Apr 15, 2008 at 3:50 PM, Frantisek Dufka <dufkaf at seznam.cz> wrote:
>
>> Michael Stepanov wrote:
>>
>>> So, how in that situation I can get correct color?
>>>
>>
>> It is already correct. The color format is RGB565. What 'correct' means to
>> you in this context? If you need the value in different format you need to
>> convert it.
>>
>>
> Yes, I need to convert RGB565 to RGB888 to compare two values - actual pixel
> color and pink color. Could you suggest me, please, some way to do that?


If you converts 565 to 888 you should do some and(&) to 888 also because 
three less meaning bits are missing from red and blue, and two bits from 
green.

so I recommend to do 888->565 conversion. Following example should work.


/* convert RGB888 to RGB565 */
.......
#define R_RGB888_OFFSET 16
#define G_RGB888_OFFSET 8

#define R_RGB565_OFFSET 11
#define G_RGB565_OFFSET 5
.......

/* get rgb888:s r,g and b */
uint8 r8 = (rgb888 & 0xff0000) >> R_RGB888_OFFSET;
uint8 g8 = (rgb888 & 0xff00) >> G_RGB888_OFFSET;
uint8 b8 = rgb888 & 0xff;

/* creates rgb565 from r8, g8 and b8 */ 
uint8 r5 = (r8 >> (8-5)) << R_RGB565_OFFSET;
uint8 g6 = (g8 >> (8-6)) << G_RGB565_OFFSET;
uint8 b5 = (b8 >> (8-5));
uint16 rgb565 = (r5|g6|b5);

uint16 rgb565_from_sdl = get_pixel_rgb565_from_sdl (...);

if (rgb565 == rgb565_from_sdl) {
   /* same value */
}
...


- Joni Valtanen