Re: RelCol Mapping of Middle Gray
Re: RelCol Mapping of Middle Gray
- Subject: Re: RelCol Mapping of Middle Gray
- From: daniel westcott <email@hidden>
- Date: Tue, 08 Mar 2005 20:08:08 -0500
Title: Re: RelCol Mapping of Middle Gray
Hi Ray,
I realized my misread immediately after hitting send but alas twas too late. Hopefully this will help.
The reference for emissive is defined as a hypothetical perfectly transmitting diffuser for PCS Lab. I think you are asking for the case of absolute transforms since relative and perceptual transforms are by definition always relative. The reference viewing environment and Medium is, AFAIK, only defined for reflective in V4 spec (D.1.4, D.1.5), And this reference only applies to the perceptual transform. Viewing is D50 at 500 lux. The medium would have 89% neutral reflectance and the darkest color would be neutral and .30911% of that 500 D50 would be reflected back.
In the absence of a defined emissive standard, one could try to emulate the standard we do have meaning the hypothetical perfectly transmitting diffuser would, hypothetically, emit 445 Lux, D50 neutral at brightest and 1.5455 lux, D50 neutral at its black point, etc. etc. Assuming everything in between was linear, this could, hypothetically, be the ideal relative transform reference monitor. (Anything outside of this must be compressed into the allowed values in the PCS space anyway) Of course things are never that easy.
Actual Practice: Taking note of the gamut map for a display profile does however provide the practical answer. That is that the PCS Lab values for an emissive source are indeed typically stated relative to the black point and the white point of the measured source and not a hypothetical standard, thus each emissive profile contains both L*=0 for V2 (3.1373 in V4) and L*=100. If it were used in practice otherwise then only the standard and anything meeting/exceeding it in spec would contain both points.
Simplified, the profile connection space is then used to define what those values mean and how they are mapped to other profiles. The luminanceTag in the icc spec along with the mediaWhitePointTag can be used by the CMM with various rendering intents then to give us what we want to see in the case of a pseudo-absolute rendering.
Practically speaking, one must optimize the display characteristics (contrast/brightness/etc) of a given device to maximize those things considered important and then measure this.
Regards,
Daniel
Ray Maxwell wrote:
Hi Daniel,
I think you are referring to transmissive. I agree with what you have said.
However, I am interested in emissive. This would be reading taken from CRTs, LCDs, and video projectors.
Thanks,
Ray
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