In the MacIntosh-forum recently somebody asked about a way to assess the maximal total ink of an image in Photoshop as in Acrobat or Indesign (probably for prepress-purposes I guess).
http://forums.adobe.com/thread/453851;jsessionid=6EFF73D4ADC319F2F24387656080AF46.node0?ts tart=0
My first idea was iterating a color-picker through every pixel of an image an collecting the values, but that seems to take a forbiddingly long time.
A way that works much quicker is bunching the four CMYK-channels into one channel by Linear Burning them with 25% opacity and evaluating the resulting channel’s histogram.
Of course that means that every histogram-step actually amounts for about 1.5% accumulated ink which still seems acceptable to me.
And with an appropriate Threshold-setting the channel can be adapted to indicate areas of certain minimal ink amounts, though non interactively.
But when working on CMYK-files with more than one additional spot color the rounding errors accumulate pretty strongly as with 6 colors one histogram-step would amount to about 2.3% total ink and the opacity for the calculation of the accumulated-ink-channel – while fine for 4 or 5 colors – has to be rounded to an integer for 6 colors.
This can be worked around to some extent by getting the channels together as layers in a grayscale-document, converting them to one Smart Object and applying the Stack Mode Mean and evaluating the result.
So I have a crude and inexact solution but does any one of You have a better idea on how to get the maximum total ink in an image with more than 4 colors in a reasonable time or does a Script for that already exist?
(If someone’s interested I can post my current Script.)