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1 2nd February 08:41
ronald_hirsch
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Default 10 step grayscale card with defined RGB values


Photoshop User Magazine had a very good article on color correction in
Photoshop using Taz Tally's 10 step grayscale card, with defined RGB values,
in the Jan-Feb issue.

I'd like to get feedback from anyone who has used his card and approach.

Also, any feedback about availability of calibrated cards would be
appreciated.

Ron Hirsch
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2 2nd February 08:42
john_slate
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Default 10 step grayscale card with defined RGB values


One would think you'd need the Lab values not RGB.
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3 2nd February 08:42
jasonsmith
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Default 10 step grayscale card with defined RGB values


Yup.
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4 3rd February 11:06
ronald_hirsch
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Default 10 step grayscale card with defined RGB values


John,

While normal profiles may use LAB, the article in question uses RGB values.
What I'm attempting to do is get feedback on the process, and locate where I
can get such a card. To get the details, one should probably read the
article, which is not an amateurish presentation. And, Taz Tally is a very
respected source.

My IT-8 card for profiling seems like more card than needed for this use.

Ron Hirsch
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5 3rd February 11:08
jasonsmith
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Default 10 step grayscale card with defined RGB values


ALL profiles reference Lab, while RGB numbers are relegated to a particular monitor profile/setup.

Lab values are universal, RGB can and usually do vary from machine to machine.
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6 4th February 12:09
ronald_hirsch
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Default 10 step grayscale card with defined RGB values


Jason,

I take no issue with what you said. But the procedure in question is not
really a profile per se.

What it does is to make color corrections similar to what the black and
white eyedroppers in Levels and Curves do, except that it's done at 10
levels of grey.

Have you seen the article???

Taz Tally is a Photoshop guru, and his procedure is certainly not whimsy.

Ron
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7 6th February 15:25
jasonsmith
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Default 10 step grayscale card with defined RGB values


I have not seen the article - but to say that RGB values will give you definitive results across the board - across thousands of users and machines is FALSE.

If Taz is really such a guru - he should know that.

Now if he explains WHICH RGB space to be in - then that would be a start.
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8 7th February 17:39
ronald_hirsch
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Default 10 step grayscale card with defined RGB values


Jason,

OK, I'm pretty well convinced, and very surprised that Taz 's article is
what it is. He also sells his calibrated greyscale card, and book.

From what I've also gathered in other text, Lab is the way to go. So, I'll
give that a whirl.

I have an IT-8 card with a file having all the values, and Gernot Hoffman
was kind enough to send me some values in January for the card.

Ron
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9 7th February 17:39
ronald_hirsch
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Default 10 step grayscale card with defined RGB values


Jason,

I just noted that I had a reply from Gernot Hoffman in my thread of January
8th, entitled "10 step grayscale target". Gernot gave me Lab values for his
IT-8 target, and I realized that I have the values for mine in the file that
I got from Wolf Faust when I bought the IT-8 target from him last year.

So, I'm going to run a test photo session, using the IT-8 target. And then,
using my Lab values, run a correction process to confirm that this will
indeed do a good job at correcting things.

If this does indeed do what I want, I'll look into using actions as much as
possible to speed up the process.

QUESTION - Lets' assume that I have an IT-8 image in one of numeruos images,
all taken with the same lighting setup. What is the easiest way to apply the
correction involved to other images.? I have tried using the new color
matching process in CS, but I didn't think it did that good a job.

I would appreciate it if you would read the message I posted to Gernot today
in the referenced thread, and offer any suggestions you can.

I didn't want to post it again in this thread, as I'd be chastised for doing
that <G>.

Thanks again

Ron Hirsch
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10 7th February 17:39
gernot_hoffmann
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Default 10 step grayscale card with defined RGB values


Ronald,

on page 6 of this updated doc is a 100 patch gray chart with sRGB and CIELab
numbers:
<http://www.fho-emden.de/~hoffmann/a3gencolortest.pdf>

One can see by PhS, using working space sRGB, that the RGB values are accurate
within +-0.5 unit of 0..255
sRGB is a "calibrated RGB space" - the RGB numbers are functions of LAB values,
only affected by rounding.

This gray chart can be used for adjusting printers by curves and of course for testing
the gray balance of calibrated printers.

Best regards --Gernot Hoffmann
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