Re: relative colorimetric without black point compensation
Re: relative colorimetric without black point compensation
- Subject: Re: relative colorimetric without black point compensation
- From: Marco Ugolini <email@hidden>
- Date: Sat, 24 Jan 2009 20:21:16 -0800
- Thread-topic: relative colorimetric without black point compensation
In a message dated 1/24/09 7:18 PM, Graeme Gill wrote:
> Marco Ugolini wrote:
>> I have not encountered any instances in which it made sense, esthetically or
>> otherwise, to blunt the dynamic range of the converted image by generating
>> blacks and shadows that look too light, as they *may* appear without BPC.
>>
>> Also, if the darkest detail in the source image is colorimetrically deeper
>> than the black point in the destination (as is most often the case with RGB
>> images that are converted to CMYK output spaces), shadows will get clipped
>> without the use of BPC, whereas BPC scales and maintains visible detail.
>
> Right, but the way I would interpret this is that what you really want to
> do is use a perceptual mapping, but typically the perceptual intent
> table has not actually been created to perceptually map from your
> chosen source to destination space (this being a fundamental problem with
> the ICC idea of creating a perceptual mapping knowing only the destination
> space), so you resort to the closest thing you have to a "smart"
> perceptual mapping, relative colorimetric + BPC.
Yes, it does look that way, Graeme.
My approach is pragmatic, and often enough using Perceptual (compared to
RelCol + BPC) sacrifices too much saturation without a noticeable gain in
visible detail.
Also, without claiming fully to understand the underlying mechanism, it
looks to me as if RelCol + BPC is often not clipping as much as we are told
it is supposed to, and instead performs a fair amount of re-mapping even of
out-of-gamut detail.
Marco Ugolini
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