[Digikam-users] Digikam internal precision?

[Greg Kennedy]

But my camera only outputs JPG - I can't get RAW out of it!  (it's
old).  So I have no choice : )

On Wed, Jan 20, 2010 at 9:39 AM, Gilles Caulier
<caulier.gilles at gmail.com> wrote:
> This is why, working with RAW file is interresting here. RAW is 12/14
> bits color depth format. digiKam store it as 16 bits color depth
> internally. All manipulation are processed with 16 bits. It's
> definitively better than 8 bits.
>
> At end you export to 8 bits with JPEG.
>
> Gilles Caulier
>
> 2010/1/20 Greg Kennedy <kennedy.greg at gmail.com>:
>> On Wed, Jan 20, 2010 at 8:22 AM, gerlos <gerlosgm at gmail.com> wrote:
>>>
>>> Il giorno 19/gen/2010, alle ore 08.40, Gilles Caulier ha scritto:
>>>
>>>> 2010/1/19 Greg Kennedy <kennedy.greg at gmail.com>:
>>>>> But would it not help, say if you were doing repeatedly lots of
>>>>> operations, to prevent loss of quality due to imprecision in 8-bit?  If
>>>>> the 8-bit numbers were expanded to 16 bit (say mul. by 256) then you
>>>>> could do all kinds of operations on them, then save the result back as
>>>>> 8-bit rounded or truncated.
>>>>
>>>> With current code to convert 8 to 16, no, because expanded histogram
>>>> has holes everywhere. Color informations are missing.
>>>
>>> This is true, after we convert to 16 bits there are holes everywhere, but after a little tinkering with the image (for example denoising, blurring, curves adjust, ...) don't we get a more uniform histogram?
>>> Image editing don't spread that color informations around?
>>>
>>> From this point of view, don't you think that working in 16 bits and truncating them back to 8 bits could be useful?
>>>
>>> These are only my hypothesis. I'm sure you can give us better explanations. Or maybe we need some experiments with some images...
>>>
>>> bye
>>> gerlos
>>>
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>>
>> Right, that was my thinking: convert 8 -> 16 (or 24, 32, etc) gives no
>> benefit until you start doing image manipulations.  Sometimes I adjust
>> white balance, then further do brightness / contrast adjust, then
>> change the saturation.  All these repeated manips done in 8-bit surely
>> have a loss in precision, while 16+ bit would help to prevent that to
>> some degree.
>>
>> (Yes I could probably do it all in one go with curves, but that's
>> unfamiliar territory for me...)
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