Hi

Am 09.05.22 um 23:00 schrieb Jocelyn Falempe:
> On 09/05/2022 18:04, Michel Dänzer wrote:
>> On 2022-05-09 16:22, Thomas Zimmermann wrote:
>>>
>>> It might also make sense to adjust the starting value of the lut 
>>> table such that its final entry is used for the final entry in the HW 
>>> palette. For typical gamma ramps ~2, the curve is fairly flat for 
>>> small values and goes up steeply at high values. (Please correct me 
>>> if I'm misinterpreting the gamma ramps.)
>>
>> I don't think that's accurate. The most common ramp should be a 
>> straight line from 0 to the maximum value, and others may be curved 
>> toward the top or bottom.
>>
>>
>>> For 15-bit case I'd do thing like this.
>>>
>>>   lut += 7;
>>>   for (i < 0; i < 32; ++i, lut += 8) {
>>>      // write  lut
>>>   }
>>>
>>> 16-bit is complicated and may better be done in 2 loops
>>>
>>>   lutr += 7;
>>>   lutg += 3;
>>>   lutb += 7;
>>>   for (i < 0; i < 32; ++i, lutr += 8, lutg += 3, lutb += 8) {
>>>     // write  r/g/b lut
>>>   }
>>>   for (; i < 64; ++i, lutg += 3) {
>>>     // write  0/g/0 lut
>>>   }
>>
>> That'll just drop the first 3-7 entries of the LUT instead of the last 
>> ones, i.e. generally the full black entries instead of the full white 
>> ones.
>>
>> Ideally, the loop should start at 0 and then count as evenly as 
>> possible up to 255/63/31. I realize that's tricky though, and I don't 
>> have any specific suggestions for how to achieve this offhand.
>>
>>
> 
> If you want 32 values from the 256 table, something like this should work:
> 
> for (i=0; i<32; i++) {
>     lut_index = i * 8 + i / 4;
> }
> 
> lut_index will have this value:
> 
> 0, 8, 16, 24, 33, 41, 49, 57, 66, 74, 82, 90, 99, 107, 115, 123, 132, 
> 140, 148, 156, 165, 173, 181, 189, 198, 206, 214, 222, 231, 239, 247, 255

Great. That's even better.

Best regards
Thomas

> 
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev