Percentage of color coverage of an image

M
Posted By
melastudio
Aug 29, 2004
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1676
Replies
6
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Closed
I need to know how much ink my laser should use printing an image… I tried to understand "histograms" and I realized that a should have to make in relation (in the right way) the number of pixel of every level of color intensity with the number of pixel of the entire image…

It’s difficult and very longer…

Is there any plug in (or another software or any other way) that helps me do it?

I’d like to know, for example, that my image contains 40% of Y, 35% of M, 12% of C and 8% of black. So I can determine the effective cost of any printed paper (and even if my supply of toner – for every color – is sufficient). In this case I see that I have a percentage of 29% of color and 8% of black (the black usually costs less).

Any suggestion
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NK
Neil_Keller
Aug 29, 2004
mela,

My 2¢ on this:

Unless you are printing, say, 1,000 of a specific image at a specific size at a specific crop on a specific stock, I think you’re spinning your wheels. Every image will have a different mix of color and I think that you’ll be spending a lot more time calculating this at your hourly rate than it’s all worth.

I’d take a more remedial approach that costs me little time and effort. I’d just see how much paper and ink I go through for, say, 100 or 1000 typical prints, and just do the simple math for a unit price based upon that.

Neil
M
melastudio
Aug 29, 2004
Thanks, Neil!
Your reasoning is based upon experience. Unfortunately, I have to do experience, yet! I’ve made a bad estimate about a job and now I realize that I’ve spent all my gain in ink!
Sometimes, especially with thousands of copies, my laser is not competitive with offset printing, so I need to lower my price near my "cost copy" in order to adjudicate myself other job…
This time I’ve mistaken only a little bit because I’ve made only 300 copies; I can’t allow that my mistake (because of inexperience) happen with thousand of copies….

The histogram provides a very large number of informations. The palette info tells the user about the % of each color for each pixel.
This is frustrating: there are all the operands but no final result!

I don’t surrender!
With your help!

Davide
JS
John_Slate
Aug 31, 2004
I agree with Neil about this one.

Toner cost should average out in the long run, and calculating usage for each project seems like going a bit far.

And the quantity is the key factor to determining the cost-effectiveness of printing on a laserprinter.

That being said, if you examine the histogram for each individual channel, you will see a "mean" number which will relate directly to ink coverage.

This formula:

(1-"mean"/255) x total area of file in square inches

will yield a square inch number that will be pretty close to all the areas of all the dots and shapes combined for each channel. So by this formula a 4 square inch file completely filled with 25%tone will yield an ink coverage area of 1 square inch.
J
jonf
Sep 1, 2004
If you’re charging so little that the cost of ink-per-print determines whether or not you make a profit, you’re charging way too little.
JS
John_Slate
Sep 1, 2004
oops

formula should be

(255-"mean"/255) x total area of file in square inches
M
melastudio
Sep 1, 2004
Thank you very much for the formula!
I’ve understood.
mean/255 gives me a number between 0 and 1 where 0 is image filled with color and 1 is image white (no color)
If I want the percentage of color coverage I have to do something like:

(1-(mean/255)) * 100.

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