Digital BW, The Print

Paul, here are the numbers:

                          Std. Deviation

0%BO:100EB6 - 0.12       10.40
20%BO:80%EB6 - 0.18      12.45 
40%BO:60%EB6 - 0.27      14.20 
60%BO:40%EB6 - 0.3       14.89
80%BO:20%EB6 - 0.49      17.29
100%BO:0%EB6 - 0.54      17.85

The numbers are correlated but my numbers show 4 times difference between BO and EB6, std dev show less then 2 times difference, to my eye 4 times looks like more correct number.

To make it crystal clear what is correct I've created an empty square image in Photoshop with gray background RGB 209, then selected 2 squares, 1/8 of full square each. Filled them with Black color RGB 38.

Now with analysis menu measurement I've got following:

  black area size  1.42  RGB 38
  gray area size    4.25  RGB 209

Smoothness: (1.42 * 38)/(4.25 * 209) = 0.0607

Std dev shows: 74.18

Then I've converted 2 squares 1/8 of the big square each into black ones. So now I have a half of square black, a half is gray.

  black area size  2.85  RGB 38
  gray area size    2.83  RGB 209

Smoothness: (2.85 * 38)/(2.83 * 209) = 0.183

std. dev shows: 85

So calculated smoothness increased 3 times which is about right, standard dev increased 10% which is not even close.

So you can't trust standard. dev, it makes inks looks too smooth relatively. 

I'm not sure what the right term should be for "smoothness", the best I can come up with is "relative specularity".

Jacob Mann
http://www.photo3dart.com