Re: Sony Artisan 1.2 Colorspaces Question
Re: Sony Artisan 1.2 Colorspaces Question
- Subject: Re: Sony Artisan 1.2 Colorspaces Question
- From: "Bertho Boman" <email@hidden>
- Date: Tue, 2 Sep 2003 11:10:04 -0400
----- Original Message -----
From: "Roger Breton" <email@hidden>
To: "Bertho Boman" <email@hidden>
>
Bertho,
>
To make the measurements, I took the time to mount the Luminance meter
onto
>
a tripod and measured at normal angle of incidence relative to the press
>
sheet which I taped onto a wall at about 5 feet from the floor. No matter
>
how much I redo the measurement I got the same reading.
>
>
If instead I place my sample press sheet in my GTI D5000 viewing booth
where
>
there is 3120 Lux illumination, I get:
>
>
White stock 650 Cd/m2
>
350% CMYK patch 40 Cd/m2
>
>
A ratio of 16.25 to 1. So, the amount of light falling on the sheet has an
>
effect on the contrast ratio. Si it seems that there are many
interpretation
>
for the concept of "Contrast Ratio".
Obviously we have a definition or measurement problem. Here are a few
thoughts:
If a white sheet is measured and it is them substituted with a sheet that is
printed all black, the ambient illumination will vary because of the change
in reflected light that will re-radiate onto the sample. The re-radiation
depends on the surrounding environment.
I assume that the meter you are using is a spot meter. Is it by chance
picking up light outside the defined spot? What about moving the meter
closer?
What happens if you move the 1000W lamp to different positions?
I would expect the best way would be to have a checker pattern printed and
then use a spot meter with a physical shield and to verify that adjacent
light from a bright patch is not affecting the reading of the black patch.
Would not the ultimate test be to measure reflectivity vs. wavelength and
then plot contrast vs. wavelength? That would visualize what is happening.
>
>
Do you have more info on this paint?
The paint is made by Behr: 1050 Ultra Pure White; Interior Flat
Actually, the best paint I measured was Munsell 6080 white reflectance
paint. It is 99% reflective in the visual range but at US$ 221.00 per 500
ml it is not very practical to use except for very specialized applications
like building integrating spheres.
Bertho
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