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Author Topic: Dot Gain & Gray Gamma. Contrast control?  (Read 6723 times)

Some Guy

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Dot Gain & Gray Gamma. Contrast control?
« on: June 09, 2014, 07:03:37 am »

Have an B&W image.

Gave it to a commercial lab to print off a SD card.  Print looks nice.

I print the same B&W image from my computer and printer (Not off the above card.), and my image looks soft and less contrasty than theirs.

I noted the image on the SD card that I got back from the lab had been altered and saved as "Dot Gain 20%."  My original was "Gray Gamma 2.20."

Does Dot Gain 20% (or whatever other percentages) control contrast, and in this case, increase it?  The two prints look like one paper grade change from the old darkroom days.

Lab said they liked the results better than "Gray Gamma 2.20" (Apple used to be Gray Gamma 1.8) by using "Dot Gain 20%" for their Epson 9900 and Epson Luster paper.  They forgot to switch it back to "Gray Gamma 2.20" when I picked it up.

I cannot see a visible difference in the Photoshop's Preview when switching between the two profiles on the screen, but the printer sure picks it up.  Don't know if it has a detrimental effect when blown up really large either, say 24x36 inches.

SG
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Slobodan Blagojevic

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Re: Dot Gain & Gray Gamma. Contrast control?
« Reply #1 on: June 09, 2014, 09:07:29 am »

What is "SD card"?

pfigen

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Re: Dot Gain & Gray Gamma. Contrast control?
« Reply #2 on: June 09, 2014, 09:34:32 am »

Well, I had a response that apparently got eaten.

Dot Gain GS spaces are for offset lithography - printing presses. The different dot gains are to compensate for the actual dot gain of the ink on the paper in the press. DG20% is the default setting in Ps. Gamma GS spaces are really for screen display but are probably less important now with color management than years ago.

If your lab is using the standard Epson printer driver to print, there are two basic ways to make a black and white print. One is to send a neutralized RGB file to the printer and let the printer profile print it as a black and white using a mix of all the available inks. That can work great if you've got a great profile or you can end up with a color cast if you don't. The second is to use what Epson calls Advanced Black and White, which is a special option in the print driver that needs sRGB files in order to work properly. Advanced Black and White prints black and white with primarily the three black inks on the 9900 and a smattering of the other colors tossed in as well, but mostly using the three blacks.

There's no way to know exactly how your lab printed the file without asking them. That your printer at home didn't match theirs is no surprise. Way too many unknown variables at this point.

There is a big difference between DG20% and GG2.2. Take a Gray Gamma 2.2 file and use the Assign Profile command in Ps to Assign Dot Gain 20 % to the file. You'll see the file get a lot lighter on screen. Of course, if you just convert from one grayscale space to another, they will look the same.

SD card?  Doesn't that stand for Secure Digital - smaller and thinner than a CF card, but the same idea. Most point and shoots use SD cards. Many pro and semi-pro cameras use both. Zoom recorders use SD cards. Etc....
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digitaldog

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Re: Dot Gain & Gray Gamma. Contrast control?
« Reply #3 on: June 09, 2014, 09:46:32 am »

Dot gain settings are for output to print, Gamma output to display. At least that's the idea behind those grayscale working spaces in Photoshop.

I suspect the lab converted the data to a dot gain for their output?
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Some Guy

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Re: Dot Gain & Gray Gamma. Contrast control?
« Reply #4 on: June 09, 2014, 11:12:48 am »

Dot gain settings are for output to print, Gamma output to display. At least that's the idea behind those grayscale working spaces in Photoshop.

I suspect the lab converted the data to a dot gain for their output?

Yes.  The lab converted my Gamma Gray 2.20 image to a Dot Gain 20% in their Photoshop and ran it through their 9900.  Looked pretty good too.  They said the like it better for B&W too over Epson's ABW or whatever it is.

When I printed off the SD card they changed to Dot Gain 20% both mine and their contrast matched in the prints.  When I printed mine at Gamma Gray 2.20 from the original that I gave them and was still on my computer, it lost contrast overs theirs and appeared very flat.

Also, if I am in PS with the file and assign either profile, and the PS "Preview" box is checked in there, I see no difference on the screen between Gamma Gray 2.20 and Dot Gain 20%.  Must be only seen by the printer then?

If Gamma Gray is for screen only, then I assume I edit with a Gamma Gray 2.20 on-screen image, and then convert it to their Dot Gain 20% if I want their printer's contrast kick.

SG
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Slobodan Blagojevic

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Re: Dot Gain & Gray Gamma. Contrast control?
« Reply #5 on: June 09, 2014, 11:17:53 am »

... SD card?  Doesn't that stand for Secure Digital - smaller and thinner than a CF card, but the same idea. Most point and shoots use SD cards. Many pro and semi-pro cameras use both. Zoom recorders use SD cards. Etc....

You are right, of course. I was reading the post too fast and got the impression the OP was talking about printing on card stock, you know, like birthday cards, or Christmas cards. My bad.

digitaldog

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Re: Dot Gain & Gray Gamma. Contrast control?
« Reply #6 on: June 09, 2014, 11:37:31 am »

They said the like it better for B&W too over Epson's ABW or whatever it is.
Advanced Black & White, another mode to print using Epson's print driver.
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Also, if I am in PS with the file and assign either profile, and the PS "Preview" box is checked in there, I see no difference on the screen between Gamma Gray 2.20 and Dot Gain 20%.
 There's no reason to be messing with the Assign Profile command in this context.
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If Gamma Gray is for screen only, then I assume I edit with a Gamma Gray 2.20 on-screen image, and then convert it to their Dot Gain 20% if I want their printer's contrast kick.
Gray Gamma is intended for screen output where dot gain is intended for print using a printing system that expects that data as specified. Both should look fine on-screen in color managed applications.
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