Forum > Sony Ericsson / Sony > Software, Firmware and Drivers > C901 camdriver modded

On 2008-10-03 15:59:51, Raiderski wrote:
guys, leave these compression settings. you will not squeeze nothing more from K800. moreover if you will stress out compression algorithm using too high values (big quality and file size) result will be opposite from planned (lower quality and small file size)

it's not possible to use 100%. of course you can always use higher value than 91% but you should remember about compression system:

1. rule #1: max jpeg file size
2. rule #2: jpeg quality
3. rule #3: both rules restrict each other

SE phones have variable compression, this means that final quality is calculated from 3 above rules. that's why your pictures don't have constant quality. variable quality is the result of fulfilled rules. ok, simple examples what can happen with 91% quality and 900kb buffer:

1. jpeg can be created with 91% and in ~900kb file
2. 91% is too much for ~900kb, quality will be decreased
3. 91% is good but file size will be much smaller than ~900kb, quality will be increased

results can be various. 800kb file with 75%-97% quality is nothing strange. now look at Goldmen's picture. he wrote that used driver had declared 100% quality, what happened in compression system? something like this:

- can I compress picture at 100% quality in ~900kb?
- no, increase compression and try again
- can I compress picture at 98% quality in ~900kb?
- no, increase compression and try again
- can I compress picture at 93% quality in ~900kb?
- no, increase compression and try again
- can I compress picture at 85% quality in ~900kb?
- no, increase compression and try again
- can I compress picture at 75% quality in ~900kb?
- yes

final result is 75% quality (according to EXIF). good conclusion...
of course we can force compression system to use very high quality but this will be useless. variable compression is really smart thing, no matter of what you won't force it to do impossibe things

On 2008-07-30 23:56:05, Raiderski wrote:
SE phones are equipped in very nice algorithm and great feature - variable compression. it is seeking the best quality % level. question: seeking? yes, this means that quality of all your pictures can be different (therefore name is variable compression). question: so, what for is 91% quality defined in driver? well, this is nothing more than simple tip for the algorithm, in this way it knows where to start process of seeking. question: ok, it knows where to start but where it ends? it's trying to predict jpeg file size with various combinations of quality % levels. predicted file size is then compared to jpeg file size rules (defined by modders in driver). if comparision will be positive then jpeg can be created, otherwise quality % level is increased (if predicted result is below defined file size rules) or decreased (if predicted result is above defined file size rules) for next file size prediction. question: does this means that defined file size rules in driver are major parameters? yes, they are, quality % level will be adequate to max file size we want to have. you can set in driver quality 100% but in fact this level of quality is unreachable in 900kb file (you can check this with EXIF readers). question: no matter of what can I set quality 100%? yes you can but for what? this is only initial stress for compression algorithm and it will blow out into dust your dreams about 100% quality

my observations:
- average file size is ~820kb (many folders, more than 100 files in each folder)
- average file size of shots with flash or low detailed scenery is ~680kb

so, I can push the rules a bit higher in next version. top quality range 90 - 95% in cameraphone? madness! with SE you guys are really in jpeg's compression heaven even if you don't believe