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Total Ink for color correction in PS

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  #1  
Old 08-22-2003, 10:52 AM
Zevs Zevs is offline
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Total Ink for color correction in PS

Hi!
Been reading in one of Scott Kelby's book about color corrections in PS. He said there that for finding a midtone spot in your picture to color correct against, you could use the Total Ink option on the eyedropper in the Info palette, and then look for a spot with the value 128. However, is there anyone who knows what this Total Ink is, is it an average of the RGB channel color values or what...? When doing this I got a very drastic color change in a picture and thought there might be something wrong. The symbol used in PS for this Total Ink is the Greek letter for the summation of values, but that doesn't seem right either. grateful for help in understanding this ...
Zevs
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Old 08-22-2003, 09:38 PM
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roger_ele roger_ele is offline
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Zevs,

I am not sure that I know the technique, although it sounds familiar.

I just ran a quick test in RGB mode and hovered over total black, the info pallette total ink read 300%, which makes sense with 100% of each ink. Second test and exactly mid tone grey reads 150%, 128 would then be a little lighter than mid grey. Maybe it is close enough for what he is doing. But, 128 is about half of 255 which is white if all three RGB colors read 255, when all three colors read 128 that is mid tone grey. If you are using curves 128 is exactly mid point, in RGB on the curve. So maybe that is what he was referring to...

I have Photo-Retouching Secrets by Scott Kelby, if that is the book throw me the page number. If not type in the paragragh and I will help you figure it out.

I have attached a screen shot of where you find total ink on the info pallette, you probably found it, but just in case.

Roger
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Old 08-22-2003, 09:44 PM
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roger_ele roger_ele is offline
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I just re-read your post, my guess is that the total ink and the 128 are two seperate things. Find a mid tone easily by using total ink (remember he is color correcting, so if a grey has a color hue it will still add up to 150%). You would then color correct that spot to be 128 with all three colors, just guessing.
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Old 08-22-2003, 10:43 PM
Zevs Zevs is offline
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Hi Roger!

Thanks for trying to unravel this! The book I was referring to was "The Photoshop Book for Digital
Photographers". What he says there on page 113 about color correcting using the curves dialog is: "Open the Info palette. By default the top-left reading shows the RGB color values. Click and hold the little Eyedropper icon on the top left and a pop-up list of measurment options will appear. Choose Total Ink. Now move the Eyedropper tool over areas in your photo that you think might be midtones, but watch the reading in the Info palette. See if you can find an area whose Total Ink reading is 128 and use that area for your midtones. Click the midtone eyedropper, to correct the midtones, and watch the change withing your photo, It can make all the difference." Have tried this now on several photos and sometimes it works OK, but sometimes it instead introduced a color cast. The symbol used in PS for this Total Ink is the Greek letter for the summation of values, but that doesn't seem right, since a summation of R 128 G 128 and B 128 would be 384 and not 128. It could be the average also but since an average could be an uneven mix of RGB colors ,e.g R 75, G 75 and B 234 that doesn't seem right either.

Zevs
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Old 08-23-2003, 12:20 AM
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roger_ele roger_ele is offline
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Open the curves dialog box and double click on the mid tone eyedropper between the white and black eyedroppers. You will notice the photoshops default setting is R128, G128 and B128, which is grey exactly half way between black and white. I think it is a typo that is close enough no one else noticed. Total ink would read 150% to equal the same brightness as the grey, even if a different color.

This will only work if, after selecting the mid-tone eyedropper from the curves dialog box, you click it on a spot that should be grey. That is what it is doing, adjusting the seperate RGB curves so that the spot you click on the photo equals the default setting of RGB in 128 each.

To understand this better, try this: If you double click on the midtone and change that to another color (try pink), click OK to close color picker dialog box, then with the midtone eyedropper still selected click on the photo, the spot you click will become pink and all other tones will reflect that curves adjustment. Go to the drop down list above the curve and change it to each of the three colors to see how it affected each curve.

Hope this helps
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Old 08-23-2003, 12:55 AM
Zevs Zevs is offline
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Thanks Roger!

Yes I guess it seems that the only way to make this work is actually finding a grey area to start with and then click on that at the point that best fits with 144 (a document filled with midtone gray (R128, G128, B128) generates the number 144/144 % in my Photoshop Info panel when Total Ink has been selected.

I think Scott's description is misleading but I think I understand now Thanks for helping me figure this one out!

Zevs
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Old 08-23-2003, 02:24 AM
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Kevin Connery Kevin Connery is offline
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Quote:
However, is there anyone who knows what this Total Ink is
Total Ink is the total percentage of inks deposited on a page for the currently specified CMYK setup. That is, how much Cyan + Magenta + Yellow + Black.

Depending on whether you've got your CMYK setup for GCR or UCR, and which CMYK space (SWOP coated or uncoated? Euroscale coated or uncoated? Newsprint?), this WILL vary quite a bit--most newspapers run a total ink limit of 280 or so, while some higher-end printers don't have a problem with 340 or even higher. All of those choices are calculated on-the-fly in the background by PS to give the one number in the info palette

In other words, it might be a very useful trick, but only if your settings are compatible--and they depend on something most non-printers don't bother to set: the CMYK conversion settings.
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Old 08-23-2003, 02:45 AM
Stephen M Stephen M is offline
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This exact issue came up a month or so ago on another list.

IMHO total ink limit readings have no place in reading netral RGB values and it only confuses things, but I can't comment on why this respected author has chosen to use this term for an RGB edit.

Total ink limits are set by the profile or conversion method to CMYK and are critical for good repro - but not for finding a neutral tone. When in RGB one should not have to worry about TIL as ink does not exist in RGB...only once the file is in CMYK mode does TIL/TIC/TAC play any role and unless there is a glitch in separation (bug) the final separations deep shadows should not be higher than the total ink limit set by the sep method. Post separation edits to CMYK can cause overinking, so good prepress alwasy checks that the TIL is right for the process at hand.

Small areas of ink cover should not matter, but any large area of coverage should be limited.

I suggest reading these links on colour correction (scroll down to the curves & levels links):

http://members.ozemail.com.au/~binar...V_links.html#C


Regards,

Stephen Marsh.
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Old 08-23-2003, 03:00 AM
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Kevin Connery Kevin Connery is offline
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Since I'm NOT a "pre-press guy", I watered down my warning, as I figured there MIGHT be some value to the approach I didn't know about.

Seems I was overly optimistic.
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  #10  
Old 08-23-2003, 07:37 AM
Zevs Zevs is offline
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Thanks Stephen and Kevin for the good replies! I will just stay away from Scott's advice on this one, there are a lot of other good ways of color correcting so it isn't really a problem. Just intrigued me why he would advice this, since I couldn't make sense of it . Thanks also for the good link Stephen!!

Zevs

http://www.pbase.com/zevs
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