[Digikam-users] jpeg from DSLR workflow: to 16bit or not

[stefan at binaervarianz.de]

>> I know jpeg is 8bit but stretching histograms in 16bit color space
>> should avoid posterization anyway. read the third tip at the end of
>> this page:
>> http://www.cambridgeincolour.com/tutorials/posterization.htm
> 
> This is wrong. Switching 8 to 16 do not feel missing data. Histogram
> will be full of holes.
> 
> To wrap around this problem you need powerfull algorithm to recompose
> histogram. There is nothing like this in opensource world.
> 

Sorry to just jump into that conversation, but I couldn't help to notice
that everyone seems to miss the question.
It's not if the picture itself gains from changing the color depth, but if
filters applied to it do.

Just a little example: Lets say his original image is that of a
checkerboard and it's encoded in just 2 bit - black and white.
Now we change the depth to 8 bit. Of course the image doesnt change. It
still has only two colors, black and white. All the new possible colors are
not used.
No gain whatsoever.

Now we apply a very heavy blur filter to both images. The original 2bit
image will transform into something resembling a black & white noise map.
Very ugly.
But the 8bit image will become a smooth gray picture. So the filter output
is improved by converting the original image to a higher color resolution.


So the answer is: it depends on the filter. If whatever you want to do with
the picture afterwards needs to create new color values for pixels, you
gain from the increased color depth.
But be aware that you need to decrease it again to save the image into .jpg
again. And you may loose anything gained beforhand depending on the
algorithm used for that decrease.

Now someone with more knowledge about digikam needs to say to which filters
this applies.


Best Regards,

Stefan