[argyllcms] Re: noise and gamut, input profiles with B2A table

To Grame:
I must to support Klaus. It may be extremely useful to introduce in tiffgamut a 
filter, downsampler and test tiff output, in a similar manner as in scanner 
chartread. It's one a problem which prevent to use Argyll CMS stand-alone.

About great gamut difference with denoising:
I do downsampling for gamut computing more often, then denoising, because most 
of denoise filters are trend to desaturate noisy areas, especially in darks. 
Denoising is prescribed in case of sparkling noise, for example at long 
exposures.
Klaus, may be Your image is very noisy, as I've seen in normalVsDenoised.wrl?
Usually I do downsampling to 12.5-25%. I'm determining the number of 
downsampling by smallest colored details, which I want to preserve good mapped. 
But I'm converting the original image without denoising.

-----Original Message-----
From: Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>
To: argyllcms@xxxxxxxxxxxxx
Date: Sun, 20 Apr 2008 20:00:57 +0200
Subject: [argyllcms] noise and gamut, input profiles with B2A table

>
> Hi Graeme,
>
> I'm just trying to gain experience with tiffgamut, profile -g and
> icclink -G and tried to test the impact of noise on the gamut size /
> gamut mapping.
>
> I applied Photoshop's denoise filter to a scan and compared the gamut
> volumes before and after denoising:
>
> I set the strength of the filter more heavy than beneficial for a
> pleasant reproduction intentionally (to allow some clipping of the noise
> in the resulting profile), but nevertheless I was very surprized about
> the result:
>
> viewgam -cn -t0.5 -s Frau-prophoto_abs.gam -ce -t0 -s
> Frau-denoise7-prophoto_abs.gam -i normalVsDenoised.wrl
>
> Intersecting volume = 54073.6 cubic units
>
> 'Frau-prophoto_abs.gam'
> volume = 222885.1 cubic units,
> intersect = 24.26%
>
> 'Frau-denoise7-prophoto_abs.gam'
> volume = 54527.7 cubic units,
> intersect = 99.17%
>
> (see also attached wrl file)
>
> I didn't create the profiles as yet, and I'm very curious about the
> results :-)
>
> Did you gain experience with the effects of downsampling, denoising or
> bluring on typical image gamuts? Did you thing about adding some kind of
> smoothing or denoising options to tiffgamut?
>
> Besides, I came across a little issue with the argyll scanner profile I
> used: Photoshop's denoise filter doesn't work with it as the profile has
> no B2A table. This is not a big issue: as a workaround one can temporary
> attach a matrix profile or convert the image to the working space, but
> sometimes I prefer working with the image in its native colorspace
> without workarounds or redundant conversions.
>
> IMHO the option to add B2A tables or additional matrix tags to input
> profiles would be nice feature. Is this possible without to much hassle?
>
> Thanks,
> Klaus
>

Other related posts: