26 Replies Latest reply on Jul 30, 2008 5:37 AM by Gernot Hoffmann

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

      Hallo, I print only to my inkjet at home, canon 4 ink epson 8 ink. In the colour management policy for photoshop cs3 within creative suite 3 I have set the Grey dot gain to gamma 2.2 instead of the default 20%. There seems to be about a 50/50 on this issue. the botom dot gain (Spot dot gain) this is not important for me.

      Could someone clarify this situation because I have found no definitive explanations on the web about this issue. Even colour management tutorils seem always to avoid these issues.

      Tankyou, Chris.
        • 1. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
          (Aandi_Inston) Level 1
          Do you ever convert your photos to greyscale? If not, I don't think
          the grey profile is ever relevant (but I'm ready to be surprised).

          Aandi Inston
          • 2. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
            Lou Dina Level 3
            Chris,

            What you do depends on a number of factors. Dot Gain is usually used when outputting to a press, since it is more likely to reflect press behavior than a gamma curve. If you had the 'average' actual dot gain for a given press, it would probably give you a closer match to a properly calibrated monitor.

            If most of your work is either displayed on web, emailed or printed on an inkjet, gamma 2.2 is probably a better overall choice. The web and email are based on sRGB, which also has a gamma of 2.2, so your grascales will display more accurately online if you use gamma 2.2. As long as you use the correct printer profiles for printing (for your paper/ink/printer), your files will be converted so they look correct on your inkjet. The more accurate your profiles, the better the result.

            Photoshop will take either your gamma 2.2 or 20% dot gain encoded file and convert the numbers to your printer profile.

            Dot gain curves and gamma curves are not quite the same. You can see the effect if you wish as follows: convert a color original to gamma 2.2. Then, ASSIGN a 20% dot gain curve. Your overall image will look lighter than the gamma 2.2 original. Try assigning 25% and 30% dot gain curves, and as the dot gain increases, your file will appear darker. Although not all parts of a dot gain curve mirror a gamma curve precisely, it appears to me that a gamma 2.2 curve is fairly close to a dot gain of approximately 27% or so.

            Probably more theory than you wanted. If you aren't going to a press, gamma 2.2 is a good bet and fairly flexible. But you can get good prints both ways.

            Lou
            • 3. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
              Level 1
              Hi Aandi, thanks for your reply, Are you Dutch? Double 'a' is a dutch dipthong, tot zo!. Lou, I appreciate your time in this, and no, it was not too technical. I need details in order to fully grasp a concept, so Thankyou.

              Chris.
              • 4. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                Level 1
                Whatever you have loaded as your grayscale working space will affect how your individual channels of a color document are displayed, so that may have an impact if you do any amount of channel work.
                • 5. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                  (Aandi_Inston) Level 1
                  No, not Dutch, sorry.

                  From what Peter says it has occasional effects on display, but still,
                  it's not a very relevant setting. Chris, what are you sort of
                  expecting it to effect? It isn't really anything to do with dot gain
                  in a general sense; it's a greyscale profile which compensates for a
                  particular dot gain WHEN WORKING IN GREYSCALE.

                  Aandi Inston
                  • 6. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                    Level 1
                    No idea Aandi. But a video podcast and a web site suggested that if you are not sending work to a printer then set this to gamma2.2 because that is the RGB space of your monitor and printer. If youare using PROPHOTO then set this setting to 1.8? Since I was used to keeping it at the default I was somewhat confused as to what to do here.

                    Chris.
                    • 7. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                      Level 1
                      Hi Peter. thanks that is an interesting point. I often use and load and manipulate individual channels, especially for sharpening. But maybe the difference are not so apparant and maybe miniscule. But thanks for that tip though.
                      • 8. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                        (Aandi_Inston) Level 1
                        > But a video podcast and a web site suggested that if you are not sending work to a printer then set this to gamma2.2 because that is the RGB space of your monitor and printer.

                        I have to tentitively say this sounds like one of those bits of
                        mythology which has no basis in real facts, but sounds convincing
                        enough that it gets repeated. It's certainly wrong in detail, because
                        it isn't an RGB space at all, and won't affect the normal display or
                        printing of RGB.

                        Aandi Inston
                        • 9. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                          (Marco_Ugolini) Level 1
                          But...it seems irrelevant to me whether or not you use a greyscale space as default that has the same gamma as your working RGB space. That has no bearing whatsoever on how the composite RGB image appears onscreen or prints or separates to a CMYK space. None at all.

                          Why would it be important to see the individual channels in the same gamma as that used by your working RGB space? What would be gained by that?
                          • 10. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                            Level 1
                            Sorry Marco, unless you are referring to photoshop channels, I do not undrstand the question.

                            Chrid,
                            • 11. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                              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
                              • 12. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                (Marco_Ugolini) Level 1
                                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.
                                • 13. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                  Level 1
                                  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.
                                  • 14. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                    (Marco_Ugolini) Level 1
                                    >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.
                                    • 15. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                      Level 1
                                      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.
                                      • 16. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                        (Aandi_Inston) Level 1
                                        > 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
                                        • 17. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                          Level 1
                                          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.
                                          • 18. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                            (Marco_Ugolini) Level 1
                                            >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).
                                            • 19. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                              Level 1
                                              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!
                                              • 20. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                (Marco_Ugolini) Level 1
                                                "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."
                                                • 21. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                  "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
                                                  • 22. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                    (Aandi_Inston) Level 1
                                                    >Really ?

                                                    Well, yes, up to that point, I didn't see any disagreement. Didn't say
                                                    there couldn't be.

                                                    >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.

                                                    But why would the colour printer be converting sRGB to greyscale at
                                                    all, if it's a colour image and a colour printer?

                                                    Aandi Inston
                                                    • 23. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                      (Marco_Ugolini) Level 1
                                                      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.
                                                      • 24. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                        (Aandi_Inston) Level 1
                                                        > 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 really. The discussion was about the general recommendation, in
                                                        some places, to choose a particular greyscale profile so a color image
                                                        prints properly.

                                                        We've been all over the place, but all we've been able to come up with
                                                        on why this advice is any use is if you might be viewing the channels,
                                                        or converting to greyscale.

                                                        Aandi Inston
                                                        • 25. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                          (Marco_Ugolini) Level 1
                                                          >Not really. The discussion was about the general recommendation, in some places, to choose a particular greyscale profile so a color image
                                                          prints properly.

                                                          I fail to see the connection...

                                                          >We've been all over the place, but all we've been able to come up with on why this advice is any use is if you might be viewing the channels,
                                                          or converting to greyscale.

                                                          Yes, which is another way of saying, although in a roundabout way, that the choice of greyscale profile (in the Color Settings, I assume) has nothing to do with the way a color image will print.
                                                          • 26. Re: Photoshop - Some professionals say dot gain 20%, others gamma 2.2 ??????
                                                            Gernot Hoffmann Level 3
                                                            Sorry, only a communication test.
                                                            Login didn't work reliably.
                                                            G.H.