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### AuthorTopic: 127,127,127  (Read 1700 times)

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##### 127,127,127
« on: January 18, 2013, 04:40:56 PM »

If I make a file all grey sRGB 127,127,127 and send it to a properly calibrated and profiled printer what should the densitometric reading of the resulting print be?

80 80 80 ?

Thanks

Duncan
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#### Czornyj

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##### Re: 127,127,127
« Reply #1 on: January 18, 2013, 05:29:10 PM »

what should the densitometric reading of the resulting print be?
0.6768
« Last Edit: January 18, 2013, 05:31:04 PM by Czornyj »
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#### Chris_Brown

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##### Re: 127,127,127
« Reply #2 on: January 20, 2013, 07:22:54 AM »

Isn't the reflective reading dependent on the paper type?
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~ CB

#### bjanes

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##### Re: 127,127,127
« Reply #3 on: January 20, 2013, 12:12:47 PM »

0.6768

I am interested in how you came up with 0.6768. For a straight gamma 2.2, a pixel value of 127 would give a density of 0.6661 according to Bruce Lindbloom's companding calculator.

To calculate the density for a pixel value of 127 in a gamma 2.2 space, one would normalize the pixel value by dividing by 255 to get a value of 0.4980. For gamma 2.2, the pixel value would be 0.4980^2.2 = 0.2157. The density would be log (1.0/0.2157) =  0.6661, which is in accord with Bruce's calculation.

For sRGB one would have to use the inverse sRGB function. The normalized sRGB pixel value would again be 0.4980. In linear terms, the value would be ((0.4980+0.055)/(0.4980+1.055)*2.4 = 0.2122. The density would be log(1/0.2122) = 0.6732

Regards,

Bill
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#### Czornyj

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##### Re: 127,127,127
« Reply #4 on: January 20, 2013, 12:28:45 PM »

I made a mistake, and copy/pasted L* value (53.1928) of sRGB 127,127,127 from Bruce Lindbloom CIE Color Calculator to Companding Calculator, but it needs "," instead of "." - and it rounded the L* value to 53, which I didn't notice at first.
« Last Edit: January 20, 2013, 12:33:11 PM by Czornyj »
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