Photoshop - Some professionals say dot gain20%, others gamma 2.2 ??????

Sorry Marco, unless you are referring to photoshop channels, I do not undrstand the question.

Chrid,

The relation between a power function (Gamma) and the
dot gain according to a simplified (!) dot gain model
is shown here on p.17:
<http://www.fho-emden.de/~hoffmann/a3gencolortest.pdf>
(preview)
<http://www.fho-emden.de/~hoffmann/a3gencolorhigh.pdf>
(quality)

As already stated by Lou, the Gamma curve for G=2.2
is appropriate if the image is treated like an RGB
image in a working space with G=2.2 (sRGB, AdobeRGB).
For instance: a color RGB image is converted to Gray-
scale and then back to RGB. It's then a gray RGB image,
which leads for many printers to a CMYK print, rich black
instead of K-only. A Grayscale (coded by Indexed Color)
is mostly printed by K-only.

In either case this is correct for desktop printers, but
not for the press, where an estimated dot gain is used or,
much better, a profile which is derived from a standard
CMYK profile like 'Black Ink ISO Coated'.

Best regards --Gernot Hoffmann

Yes, I am referring to the channels as one views them in Photoshop, as I wrote in my reply.

The question is: Why would it be important to see the individual R, G and B channels in greyscale in the same gamma as that used by your working RGB space? What would be gained by that, since the composite image is not affected by the gamma of the default greyscale space as defined in the Color Settings?

I hope my question is clearer now.

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.

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.

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.

> My whole original question was about the setting in the colour management dialogu box with regard to actual printing.

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

It is NOT a dot gain business. It is the choice of greyscale profile,
some of which simulate dot gain when working with greyscale. You
aren't, right?

I imagine they didn't mention greyscale profile because it isn't
relevant, and the other two just subscribed to myths. Be very wary of
ALL the advice in those two tutorials, it sounds as if they don't know
what they are talking about, but are just repeating their favourite
from the advice they've picked up. (Unless someone can advise me
otherwise).

Aandi Inston

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.

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).

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!