Re: camera colour spaces
Re: camera colour spaces
- Subject: Re: camera colour spaces
- From: email@hidden
- Date: Tue, 11 Mar 2008 11:36:21 -0500 (EST)
- Importance: Normal
Thank you for your help understanding. The picture is getting clearer. I
think I understand the concept of output referred¨, and it really doesn't
surprise me, nor bother me, to know that camera manufacturers are
embellishing the capture to fit generic pictorial conventions as opposed
to accurate colour rendering. But I am still, after much time and
concentrated effort, unable to imagine how this rendering takes place
without a profile. I have come to the conclusion that this rendering that
occurs before encoding has to be an icc profile otherwise I cannot follow
the data flow.
Using the example of a neutral grey card that, if we had photographed in
3200k light using a tungsten custom camera profile and then subsequently
converted to srgb, would have produce RGB=128 and L*54, 0, 0 in srgb. If
we photograph the same grey card without the input camera profile, camera
settings would indicate a white balance of 3200k but the data itself would
not be decipherable as neutral grey. It is possible that control signals
resulting from the capture produce R=122 V=147, B=119 to which a custom
input profile would have assigned the chromatic value 54, 0, 0 in order to
pivot to the srgb data of RVB= 128. But without the input profile I cant
find the bridge from data to colour. Even if the manufacturer wanted to
deliberately warm or cool this grey he would first need to know how the
camera responds to grey.
The only way my limited understand of colour management is able to
understand this in- camera rendering is to see it as a cryptically
assigned generic input profile followed by an imposed conversion to a
selected colour space. The choice of rendering I can only see as different
input profiles, each one with its own table, or a single input profile
using different custom rendering intents, much as some profile
manufactures use the saturation intent to flavour the colour pallet,
(apparently there aren't any icc standards for this intent.)
Am I mistaken or is this rendering simply an input profile with a mandate
other than accurate colour rendition
Paul Lowy
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