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Author Topic: RGB numbers?  (Read 7032 times)

David Hufford

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RGB numbers?
« Reply #20 on: May 16, 2010, 12:37:12 AM »

Quote from: Guillermo Luijk
Offtopic question: just curious, are American students now learning at school/university inches or cm? miles or Km? Celsius or Farenheit?
I studied that in grade school, then quickly forgot most since it is generally irrelevant to people living in the US. We hardly ever use it. It's not really something for university-level study anyway as the conversion is simple. But after more than a decade of living in a country that uses the metric system, I still find the Celcius temp reading less intuitive and a more general, less nuanced---if that's the word---way of defining the temperature.
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DarkPenguin

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RGB numbers?
« Reply #21 on: May 16, 2010, 02:01:12 AM »

Why not just mentally multiplying the percentages by 2.5 in your head until you're used to them?

Quote from: Guillermo Luijk
Offtopic question: just curious, are American students now learning at school/university inches or cm? miles or Km? Celsius or Farenheit?

Back in grade school history's greatest monster (Jimmy Carter) had us learning it.  Then Ronnie Raygun got into power and put the kibosh on that and we went back to rods and hogs heads for measurements.
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Peter Stacey

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RGB numbers?
« Reply #22 on: May 18, 2010, 03:56:24 AM »

Quote from: DarkPenguin
Why not just mentally multiplying the percentages by 2.5 in your head until you're used to them?

For all the reasons earlier in the thread, that approach won't help much.

To show it graphically, the following image shows the percent values in Lightroom 3 Beta 2, followed by the same image converted to ProphotoRGB, AdobeRGB and sRGB in Photoshop.

Multiplying the percent values by 2.5 doesn't give the same values in the different output profiles:



For the specific values, the following table might show it more clearly than the image, including the 2.5 multiplier of the percent values:



The target image can be downloaded here:

target.psd
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digitaldog

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RGB numbers?
« Reply #23 on: May 18, 2010, 09:30:13 AM »

Quote from: Peter Stacey
The target image can be downloaded here:

Thanks for taking the time to build that. Most useful as a teaching aid for this topic!
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Andrew Rodney
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elied

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RGB numbers?
« Reply #24 on: May 18, 2010, 10:00:31 AM »

Quote from: digitaldog
Thanks for taking the time to build that. Most useful as a teaching aid for this topic!

d.d. - Are the LR numbers ProPhoto corrected to gamma 2.2 instead of 1.8?
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digitaldog

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RGB numbers?
« Reply #25 on: May 18, 2010, 10:02:46 AM »

Quote from: elied
d.d. - Are the LR numbers ProPhoto corrected to gamma 2.2 instead of 1.8?

In LR, the numbers use the actual sRGB 2.2 TRC.
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Andrew Rodney
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