Re: how to determine the Ambient White Point?
Re: how to determine the Ambient White Point?
- Subject: Re: how to determine the Ambient White Point?
- From: Robin Myers <email@hidden>
- Date: Tue, 11 Jun 2002 13:27:52 -0700
- Organization: Robin Myers Imaging
Jirtme Louradour wrote:
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Hello,
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I am wondering how to determine the ambient white that is considered to
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make the conversion from (X,Y,Z) to (L,a,b) or (L,u,v).
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1- For the norm sRGB, I have the 'x' and the 'y' (of the D50), but how can
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I get the ratio (Y ambient white)/(Y computer white 255,255,255)? I have a
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Display Luminance level (cd/m2) and a Reference ambient illuminance level
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(lux), but i don't know how to deal with these data.
In practice the Y of the light source is taken to be 100 (or 1 if the
scale is 0 to 1). This is due to adaptation of the human visual system.
Thus, the D50 white point would be represented as x 0.3457, y 0.3585, Y 100.0.
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2- In practice, how to measure the Ambient White Point?
A spectrophotometer that can measure emissive devices is used. Low cost
spectrophotometers include the GretagMacbeth Spectrolino and the X-Rite
Colortron II.
Robin Myers
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