CMYK

[iosoio]

Hello.

I converted a set of sRGB images to CMYK via the Blurb ICC profile and found how this profile added a lot of light blue cast (Cyan) opening up the shadows. As a consequence the printed pages have a yellow/greenesh deviation which is well perceivable on B&W pictures, especially if lustre paper is used; much less with the matte finishing.

So I used the hystogram levels to correct the ICC profile conversion by setting the Cyan gamma to 0.96 and the Magenta to 1.02, so to have a better approximation of the neutral grey: In RGB the Red, Green and Blue values are now the same.

Now the question. Playing with the channels gamma arrow (the central one) I've noticed that, while toward right it reaches 0.10, toward left it stops at 7.64; the measurement unit being set to percentage.

What does this 7.64 value exactly signify?

Please, consider how my experience with the above mentioned subtractive colour system is close to zero. So be kind in case I've said or done some stupid thing:-)

Thank you

[Martin Huber]

I converted a set of sRGB images to CMYK via the Blurb ICC profile and found how this profile added a lot of light blue cast (Cyan) opening up the shadows.

I don't have a blue cast here with the rendering intents "Perceptive" and "Relative Colorimetric". I do get a blue cast with "Absolute Colorimetric", but it is quite unusual to use this rendering intent.

As a consequence the printed pages have a yellow/greenesh deviation which is well perceivable on B&W pictures, especially if lustre paper is used; much less with the matte finishing.

So I used the hystogram levels to correct the ICC profile conversion by setting the Cyan gamma to 0.96 and the Magenta to 1.02, so to have a better approximation of the neutral grey: In RGB the Red, Green and Blue values are now the same.

Unless you are really knowing what you are doing, you shouldn't post process CMYK values.

Now the question. Playing with the channels gamma arrow (the central one) I've noticed that, while toward right it reaches 0.10, toward left it stops at 7.64; the measurement unit being set to percentage.

What does this 7.64 value exactly signify?

It doesn't have a special meaning. The middle arrow is used to control the gamma value and represents the 50% value of the image data. If you drag it to a different position, PhotoLine computes the gamma value needed to move to 50% value to that position.

Martin

[iosoio]

I converted a set of sRGB images to CMYK via the Blurb ICC profile and found how this profile added a lot of light blue cast (Cyan) opening up the shadows.

I don't have a blue cast here with the rendering intents "Perceptive" and "Relative Colorimetric". I do get a blue cast with "Absolute Colorimetric", but it is quite unusual to use this rendering intent.Martin

Hi. I do use Perceptive as the rendering intent and the addition of Cyan must have the consequence of the Indigo printers calibration made by those of Blurb. I didn't mean Photoline it's responsible for this.

There is a confirmation in the mix of inks Blurb suggests to generate the black; which is 60C, 50M, 50Y and 100K. A sort of rich black where the Cyan is more than the Magenta and the Yellow.

By the way, Relative colorimetric shouldn't affect the colour balance at all, since it changes just the exceeding part of the input colour space: those colours that are not reproducible in the output colour space.

As a consequence the printed pages have a yellow/greenesh deviation which is well perceivable on B&W pictures, especially if lustre paper is used; much less with the matte finishing.

So I used the hystogram levels to correct the ICC profile conversion by setting the Cyan gamma to 0.96 and the Magenta to 1.02, so to have a better approximation of the neutral grey: In RGB the Red, Green and Blue values are now the same.

Unless you are really knowing what you are doing, you shouldn't post process CMYK values.Martin

I agree, but I was experimenting for removing an unpleasing greenish cast and I succeeded: the re-print is now correct, the grey is much more clean. The problem is that the ICC profile is just one, while the papers are of five different kinds; each of which reacting differently to the radiant spectrum of the light.

Now the question. Playing with the channels gamma arrow (the central one) I've noticed that, while toward right it reaches 0.10, toward left it stops at 7.64; the measurement unit being set to percentage.

What does this 7.64 value exactly signify?

It doesn't have a special meaning. The middle arrow is used to control the gamma value and represents the 50% value of the image data. If you drag it to a different position, PhotoLine computes the gamma value needed to move to 50% value to that position.

Martin

Thank you

[iosoio]

I converted a set of sRGB images to CMYK via the Blurb ICC profile and found how this profile added a lot of light blue cast (Cyan) opening up the shadows.

I don't have a blue cast here with the rendering intents "Perceptive" and "Relative Colorimetric". I do get a blue cast with "Absolute Colorimetric", but it is quite unusual to use this rendering intent.Martin

Hi. I do use Perceptive as the rendering intent and the addition of Cyan must have the consequence of the Indigo printers calibration made by those of Blurb. I didn't mean Photoline it's responsible for this.

There is a confirmation in the mix of inks Blurb suggests to generate the black; which is 60C, 50M, 50Y and 100K. A sort of rich black where the Cyan is more than the Magenta and the Yellow.

By the way, Relative colorimetric shouldn't affect the colour balance at all, since it changes just the exceeding part of the input colour space: those colours that are not reproducible in the output colour space.

Sorry, I have misread your sentence. You said "Absolute" and I replayed about the "Relative" colorimetric rendering intent. Yet, in my specific case there should have not been any practical difference, because the input files were mostly grayscale pictures (scanned in greyscale with Vuescan or converted in Photoline with the grey mixer) and thus no white point shift could have taken place in the relative colorimetric conversion; as far as I know the only difference with the Absolute colorimentric intent.

Bye

[iosoio]

Hi,

when I convert to CMYK in Photoline, which model is used for performing the transformation? I mean: If I convert to CMYK by the above mentioned Blurb ICC profile, a derivation of the GRACoL2009 is applied; so, what is used when I simply switch from RGB to CMYK in the Layer Property panel? And then, how can I restore this "Generic" CMYK colour space from a custom one like the GRACoL2009?

One more question: How much lossy is a double color conversion, a part from the loss of those colours that each time could not be encompassed in the outgoing colour space?

Many thanks

[bkh]

when I convert to CMYK in Photoline, which model is used for performing the transformation? I mean: If I convert to CMYK by the above mentioned Blurb ICC profile, a derivation of the GRACoL2009 is applied; so, what is used when I simply switch from RGB to CMYK in the Layer Property panel?

PL uses the default CMYK profile, i.e., the CMYK profile of the enclosing group if present, else the document CMYK profile if there is one, or finally the standard CMYK profile set in Preferences -> Colour Management -> Standard.

And then, how can I restore this "Generic" CMYK colour space from a custom one like the GRACoL2009?

You can use "Convert With Colour Profile", but you'll have to find out the destination profile first (see above). After the conversion, you can delete the layer profile (in the Layer Attributes panel, or use "Set Profile" and select "No Profile") if you like – this should not have a visible effect, otherwise you converted to the wrong profile.

One more question: How much lossy is a double color conversion, a part from the loss of those colours that each time could not be encompassed in the outgoing colour space?

Should be ok if you work with 16 bits of colour depth. 8 bit is a bit risky, in my experience. Btw., if you want to do a RGB -> CMYK conversion (or viceversa) and want a certain destination profile, you can do so using "Convert With Colour Profile" – in many cases, this avoids the duplicate conversion.

Cheers

Burkhard.

[iosoio]

bkh, I have a dubt: Photoline default settings are to pick-up the system profile for both RGB and CMYK, but I have just one system profile set at system level on my Windows 7 pro, and this is sRGB, because it's the most conservative colour space for displaying content in any LCD monitor; certainly with my Dell one.

So, what I have to do to make Photoline detecting a system CMYK profile? Have I to add a CMYK profile from the (long) list appearing when I push the add profile in the W7 Colour Management control panel? Letting the sRGB as the default profile? And in this case, which one can be considered the best approximation of a generic, all pourpose CMYK profile: the most "abstract" CMYK profile?

I say this because there are many standards and often for coated and uncoated papers... Finally, what profile is picked-up by Photoline when no CMYK profile has been set at a system level?

Thank you very much.

[bkh]

So, what I have to do to make Photoline detecting a system CMYK profile? Have I to add a CMYK profile from the (long) list appearing when I push the add profile in the W7 Colour Management control panel?

Sorry, I don't know anything about Windows colour management, but in any case, you could just change PL's standard CMYK profile to anything you like.

Letting the sRGB as the default profile?

sRGB as the default RGB profile definitely makes sense. Most images without profiles are sRGB, or at least look ok as sRGB.

And in this case, which one can be considered the best approximation of a generic, all pourpose CMYK profile: the most "abstract" CMYK profile?

There is no "standard" CMYK profile, afaik. ISO Coated/Fogra39 is kind of a standard in Europe, and "Web Coated" seems similarly popular in the US, there are variants of both with only 300% ink which are safer to use (http://www.ne14design.co.uk/articles/wh ... rofile.htm). In any case, imo CMYK really only makes sense if you use the CMYK space which corresponds to the printing process – otherwise, you can stay in RGB and use your printer's proofing profile for fine-tuning.

Cheers

Burkhard.

[iosoio]

You're right, Bkh: there is no ONE stantard CMYK profile and when an application relys on the Operating System to make the conversion, this should fail if no System CMYK profile is choosen. At least it seems so reading this Microsoft support page for Windows Vista (I have found anything specifically referred to W7).

https://support.microsoft.com/en-us/kb/933845

So I wander thinking what the hell is going to happen when in Photoline someone switches from RGB to CMYK not having changed its default settings for the colour management... Martin should probably spend a word on this point.

The confusion is aggravated by those software houses frequently calling their presets "Generic CMYK" (Quark) Standard CMYK (Microsoft) etc.

From the above linked page it's now clear how Microsoft called "Standard CMYK" what in reality is nothing more than the SWOP, one of the very many, and installed it with the Office suite!

The problem exists because I've decided to convert my images to CMYK one at a time to manually choose the best rendering intent for each; and because I've had to over-correct the final result chasing the best possible gray scale neutrality. What a Chimera.

In conclusion I've opted to leave all of the pictures in the Blurb CMYK (GRACoL2009) and if one day I had to make the book printed by someone else I'll convert everything from the Blurb colour space to the new one by the "Convert to Colour Profile" in Photoline or what else DTP application during the final export phase.

Thank you very much

Ps. There's a lack of English localization in the Colour Management settings of Photoline, where the option for choosing Little CMS as render engine and for the black point compensation has been left in German.

[Martin Huber]

So I wander thinking what the hell is going to happen when in Photoline someone switches from RGB to CMYK not having changed its default settings for the colour management... Martin should probably spend a word on this point.

Windows doesn't have a default CMYK profile, so on Windows PhotoLine installs a local CMYK profile ("ISO Coated v2 (ECI)") and uses that as "System" CMYK profile.

Martin

[iosoio]

So I wander thinking what the hell is going to happen when in Photoline someone switches from RGB to CMYK not having changed its default settings for the colour management... Martin should probably spend a word on this point.

Windows doesn't have a default CMYK profile, so on Windows PhotoLine installs a local CMYK profile ("ISO Coated v2 (ECI)") and uses that as "System" CMYK profile.

Martin

Hello,

can you confirm that ("ISO Coated v2 (ECI)") is 2009 FOGRA 39, ISO Coated v2? With max ink coverage = 300%, which anyway is a quite conservative limit, today.

According to the ECI documentation this can be considered a good "generic" CMYK profile...
http://www.eci.org/doku.php?id=en:colorstandards:offset

In general, the ECI, bvdm, and Fogra recommend using the ICC profile which matches the intended printing condition, for colour conversion as well as for proofing. You will find an overview of all ECI offset profiles for standard printing conditions in the PDF manual on page 4. Some paper manufacturers and suppliers provide information regarding recommended characterization data sets (Fogra number) and ECI offset profiles according to the paper stock. The ECI offset profile “ISO Coated v2 300% (ECI)” is a good choice in cases where the intended printing condition is not yet known. The advantage of the version of the coated profile with a maximum total ink coverage of 300% is it‘s higher flexibility regarding the use for sheetfed and web offset printing. Prepress data prepared with this profile can be converted to many other printing conditions with good results, however, the best possible results will be achieved with cmyk prepress data prepared with the profile that matches thatprinting condition exactly.

Thank you

By the way, as long as every pdf embeds the colour profile, which I suppose the reason that makes Acrobat to correctly visualize a CMYK document, without being installed its profile at a system level, the final conversion could possibly be performed by the printing company.

-

Postscript.
In case you want to take a look, both files, the book and the dust jacket, have entirely edited in Photoline: from RAW to CMYK. I've had to give up the aim of laying out all the pages in Photoline, though, because of some limitation in typography and some discomfort here and there. The dust jacket has been drawn in Photoline.

It' a 96 dpi downscaled version without registration marks to be seen by activatiing the Display > Two Page View in Adobe Acrobat.

https://www.dropbox.com/s/pu9w9viw6fyyr ... i.pdf?dl=0
https://www.dropbox.com/s/h3h8m7bp611j6 ... i.pdf?dl=0

[Martin Huber]

can you confirm that ("ISO Coated v2 (ECI)") is 2009 FOGRA 39, ISO Coated v2? With max ink coverage = 300%, which anyway is a quite conservative limit, today.

No, it's exactly the profile I wrote.

Martin