[Digikam-devel] [Bug 148540] Improvements of adding noise tool

Gilles Caulier caulier.gilles at gmail.com
Tue Mar 23 15:37:27 GMT 2010


Gilles Caulier <caulier.gilles at gmail.com> changed:

           What    |Removed                     |Added
             Status|RESOLVED                    |CLOSED

--- Comment #51 from Gilles Caulier <caulier gilles gmail com>  2010-03-23 16:37:15 ---

I think the chrominance noise generator is not too bad, excepted in shadows and

Conversion in YCbCr color space is done in floating point to prevent rounding
error. Noise is added to Chroma red and blue chanels and clamped to prevent

But, with highkey or lowkey photo, color are saturated if noise is too
important. I don't know why exactly, but i suspect a problem with the
"footroom" and the "headroom" values as explained in wikipidia page :


In this page these ranges are defined for 8 bits color depth integer conversion
matrix, not for floating point conversion matrix. So i have a doubt here, but i
think that clamping values must be adjusted accordingly [not clamp(0.0, 1.0,

What do you think about ?

Gilles Caulier

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