Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????

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G.H.

I may have missed something along the thread, but I thought this discussion was about the effect of the default greyscale profile in Photoshop's Color Settings on the viewing of a file's individual channels -- not about converting a color image to greyscale.

Am I incorrect about that? If I am correct, I fail to see the relevance of Gernot's comment.

"I think every reply so far has agreed there is absolutely
no effect on colour printing."

Really ?
If we convert sRGB to Grayscale by G=2.2 we get one set of
numbers (image1). If we convert RGB to Grayscale by G=1.8
we get a different set (image2). Now let's assume that no
profile is embedded, or not input profile can be defined.
Then the printer assumes probably G=2.2 and the print of
image2 would be wrong.

Bad as well for press printing as PDF/X-1a. One conversion
for dot gain 28% (or so) because of G=2.2. The other for
dot gain 20% or by using a more accurate gray profile:
the first print would be very wrong on coated paper.

Using a qualified RIP, Grayscales are printed correctly
for three cases:
a) the profile is embedded and honoured by the RIP.
b) the profile is not embedded but chosen explicitly as
required.
c) G=2.2 was chosen and the RIP assumes this always (bad).

Best regards --Gernot Hoffmann

"Cum grano salis" does NOT translate into "don't believe anyone"!

It only means that you take the information, test its validity for yourself, and then you can rave about it if it works and toss it if it doesn't.

It means "be patient" and "take the time to try things out."

If we had to 'cum grano salis' then nobody would be able to learn anything would they. I mean, you want an answer....you read the answer.....you doubt what you read.....you read another answer.....you doubt what you read....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....youdoubt what you read......you read another answer.....and so it goes on. Someone somewhere has to be trusted..............

Chris. quam clarem!

>when you read something written by someone who is professional (books published, intricate website0 THEN ONE WONDERS ... COULD THIS BE TRUE?

Well, each of us has his/her limits, including those who have written books on the subject.

As people far back in time as the Romans used to say, take it all "cum grano salis" (with a grain of salt -- meaning with caution and a healthy dose of "questionable-until-proven" skepticism).

Well Aandi your last paragraph is undoubtedll very true. When one begins to learn new concepts one does not have the luxury of trusted tutors in a classroom. I have to rely on books and websites. This is not an easy process because as you rightly imply, I have to learn to sift, which i do, by reading many peoples' instructions. trouble is, when you read something written by someone who is professional (books published, intricate website0 THEN ONE WONDERS ... COULD THIS BE TRUE?

thanks anyway

best regards

Chris.

ok, now I understand. My whole original question was about the setting in the colour management dialogu box with regard to actual printing. This dot gain business was avoided by all the videos and tutorials except two that simply mentioed that if you are a home printer then set it to gamma 2.2 and not leave it on its default. that was it.

>the link between the channels and this dot gain does not make any sense to me to be honest.

It's very simple, in a way.

Image files in Photoshop (RGB or CMYK) are made of channels. Channels can be viewed individually (one at a time) in the Channels palette (sorry, in CS3 palettes are now called "panels"...).

Channels are viewed either in the color of the channel (Red, Green, Blue, etc.), or in greyscale (you choose which of the two in Photoshop's Preferences > Interface > Show Channels In Color).

When you view the channel in greyscale, the contents of that channel are shown using the same gamma or dot gain setting as that of the default greyscale space selected in your individual Color Settings. If your default greyscale is "Gray Gamma 2.2", the individual channel is shown with a gamma of 2.2. That's all there is to it.

But the default greyscale gamma has no effect whatsoever on how the *composite* image appears (RGB or CMYK, with ALL channels showing at the same time). No matter what your default greyscale space is, the composite RGB or CMYK image will look exactly the same. That was the point I was trying to make.

Hi Marco, I think things are becoming too complex for me now. I am a photoshop person dealing in photographs. I use channels as part of my editing. the link between the channels and this dot gain does not make any sense to me to be honest.

Best regards

Chris.