Luminous Landscape Forum

Raw & Post Processing, Printing => Colour Management => Topic started by: dhasker on January 18, 2013, 04:40:56 pm

Title: 127,127,127
Post by: dhasker 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
Title: Re: 127,127,127
Post by: Czornyj on January 18, 2013, 05:29:10 pm
what should the densitometric reading of the resulting print be?
0.6768
Title: Re: 127,127,127
Post by: Chris_Brown on January 20, 2013, 07:22:54 am
Isn't the reflective reading dependent on the paper type?
Title: Re: 127,127,127
Post by: bjanes 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
Title: Re: 127,127,127
Post by: Czornyj 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.