Grey balance test

[gordo]

Within the next couple of months I will have the opportunity to test the relationship between a grey balance patch with the live image area. This will be on a coldset newspaper press. I don't believe that 3/C grey balance patches in color bars are valid indicators of what is occurring in the live image are...but I'm happy to be proved wrong. So, in this test I will be running several types of images - after the press has been G7'd into grey balance. We'll raise the Cyan SIDs from normal to at least 20 points higher. The idea is to see how the images respond to the shift in Cyan vs the appearance of the grey balance target in the color bar. To facilitate a measured approach to a subjective approach I am thinking of using standard images with their mosaiced versions. The mosaiced version can be measured - something like this.

The left image is the original - the right is the measurable mosaiced version. Subjective vs measurable.

Any thoughts or suggestions? What would you add to this test.

best, gordo

 

[Stephen Marsh]

Just a thought Gordo, you could ensure at least two of the patches in the live image area also reflect the build of the colour bars found off the page. In theory they should both move the same...however in practice? For example a 50k and a 45c36my patch next to each other (if this was ISO Coated/F39, obviously your build may be different). Or perhaps 3 grey balance patches (25%, 50%, 75%) or 3k and 3cmy grey balance.


Stephen Marsh

 

[Louis Dery]

Hi Gordo,

For this gray balance respond test, you have to test your images with different black generation (GCR, etc.). If you apply a strong GCR seps to image and then try to raise Cyan, for example, the image won’t respond as much as if your image was separated with a UCR separation.

I would do test with different black generation images for such test.

Best regards,

Louis

 

[jstotz]

It may not matter for what you are doing, but the algorithmically generated mosaic version doesn't necessarily represent the full gammut of the image. For example, none of the red patches represent the color of the red circle on the wall. Because of how they are positioned, they are blended with other background pixels. It also probably has several duplicate or near duplicate patches. You might want to go in and edit some of the patches to better represent actual significant colors in the image.

 

[Deleted member 16349]

Within the next couple of months I will have the opportunity to test the relationship between a grey balance patch with the live image area. This will be on a coldset newspaper press. I don't believe that 3/C grey balance patches in color bars are valid indicators of what is occurring in the live image are...but I'm happy to be proved wrong. So, in this test I will be running several types of images - after the press has been G7'd into grey balance. We'll raise the Cyan SIDs from normal to at least 20 points higher. The idea is to see how the images respond to the shift in Cyan vs the appearance of the grey balance target in the color bar. To facilitate a measured approach to a subjective approach I am thinking of using standard images with their mosaiced versions. The mosaiced version can be measured - something like this.



The left image is the original - the right is the measurable mosaiced version. Subjective vs measurable.

Any thoughts or suggestions? What would you add to this test.

best, gordo

This should be interesting but I am not sure how much it will tell you. I would expect that a change in the image will probably also show up in the gray patch. Which is more sensitive to the change in the ink setting will probably not be consistent for different parts of the image.

Of course the real problem of printing is whether the image can be produced with reasonably accurate colour at every point in the image with respect to the original. G7 and other of the curve methods are not sufficient to ensure this will happen.

Also the other major problem is that even if the image can be reproduced, the consistency of the run is important. Todays presses are better than in the past but they are still not capable of running consistently. If they could, there would be not talk of closed loop systems and visual changes in gray patches.

But back to your testing. I think it will be interesting and it may show up other issues that you were not expecting. Testing always does if one looks closely at the results and thinks about what they mean. Have fun and let us know.

Question. Are you printing the mosaic version?

 

[meddington]

Image content will certainly play a factor. For example, if you boost cyan density, you may more readily see/measure a change in the soccer player with the cyan clothing, while the rest of the image may show less effect of the increase, particularly with a GCR'd image. If you have predominately magenta subject matter in the imagery, you may not see an effect of a cyan increase at all. So though a gray balance patch may be rather loosely tied to the live press area (depending on image content), it can be indicative of a potential issue, and may be useful as a goal post while running. Something similar can be done synthetically in Photoshop for example, only adjusting curves rather than raising densities. Just my 2cents.

Interesting test. looking forward to your results.

 

[jaed]

it's just a thought but... raising the SID's will affect the image by changing things like the Lab values of the cyan ink, the trap values of all of the overprints and the amount of mechanical dotgain on press.
You could try and put the same image side by side with one having slightly higher Cyan Dot values, maybe 5%-10% or so, and creating a custom color bar for that side that has the same 5%-10% added to the gray patches. This way the only thing that changes between the two images is the final amount of Cyan. The gray balance in the patches will be way out of wack but you can compare the two printed images visually to see what the difference is with out changing all of those other variables.

I'm not sure if this will help but I hope it does.

P.S. Are you done posting on your "The Print Guide" blog, it was a great place to get some good ideas and insight in to things.

 

[gordo]

[SNIP]

P.S. Are you done posting on your "The Print Guide" blog, it was a great place to get some good ideas and insight in to things.

I've somewhat lost my motivation for continuing posting to my blog. It was a lot of work to do but not getting any donations even though I know it's helped printers and buyers solve their problems. Heck, I've helped printers and print buyers who contacted me through the blog and not even gotten a thank you from them. So I feel I've done what I originally wanted to do but there's nothing in it for me to continue.

Thanks all for your suggestions regarding the grey balance test.
This newspaper publisher currently balances color on the press by eye - there are no QC targets. Their RIP applies ink optimization using heavy GCR techniques to reduce ink usage.
Part of my intent with the test will be to show the press operators how their twiddling of SIDs has or does not have an effect, other than placebo) on the imagery. So I'll be using several images (high key, low key, neutral and heavily saturated images) that represent the typical images that they print.
The test will be done double truck (the center spread of a broadsheet newspaper section - where content is across both pages, including the gutter between the pages).
The left side will have images that were separated using standard newspaper profiles.
The right side will have the same images but reseparated using their ink optimization system.
The press will be brought up to SNAP densities (at which point their Lab values happen to fall right into place).
We'll pull sheets as we go up to density, at density, and then pushing one of the colors (cyan or magenta) to see how the SID change affects color on standard separated images and on ink optimized images. That way the press operators (who don't understand densitometry or dot gain) should get a subjective insight into how color reacts to SID moves. The mosaiced version of the images simply allows the color of the images to be measured. I.e. on the left the subjective image and beside it the objective measurable image.
Meanwhile, I can measure how the grey balance bar reacts relative to different types of images (standard and ink optimized) and see if my theory is correct (i.e. grey balance patches are too sensitive to be useful in production printing).
Ultimately I want them to have some QC targets included in the newspaper and that they run to the numbers rather than eyeball color. If my theory is proven then the QC patches may likely be solids only (like USA Today) or a grey balance patch from which SIDs can be determined.

That's basically the idea.

best, gordo

 

[CD102]

Gordo,

Sorry to hear that your blog is done. I went there a few times and it was always interesting even if it was at times too technical for this seat of his pants printer.

 

[gordo]

Gordo,

Sorry to hear that your blog is done.

Me too. Thanks. Gordo

 

[gig0]

I've somewhat lost my motivation for continuing posting to my blog. It was a lot of work to do but not getting any donations even though I know it's helped printers and buyers solve their problems. Heck, I've helped printers and print buyers who contacted me through the blog and not even gotten a thank you from them. So I feel I've done what I originally wanted to do but there's nothing in it for me to continue.

If it means anything at this point, thanks Gordo. I never contacted you, but referenced your blog a few times to learn something new, get me out of a jam or just to get a better refresher course on getting back to basics. Your effort didn't go unnoticed. I just want you to know I appreciate you sharing your knowledge. Yes, it's Friday night and I'm drunk, but I love you, man.

 

[jaed]

Hey Gordo, did you ever get a chance to run this test? If so is there a link to the results?

 

[gordo]

Hey Gordo, did you ever get a chance to run this test? If so is there a link to the results?

Not yet because this publisher still has to upgrade their workflow. But when I do - and I will - I will share the results here for sure.

Best, gordo

 

[geckowraps]

Quit interesting, Thanks for sharing it.

 

[BeauchampT]

About gray balance patches....I agree that they are ultra sensitive and not very helpful if you are printing high contrast images. If you are a shop that prints very low contrast brown, and pastels, I have found it to be a useful tool. One thing I am curious about is your thoughts regarding effect of paper white point on your gray balance....I see this causing some very interestnig hue shifts sometimes.

Actually, you can almost mathmatically shift your gray balance to match a contract proof simply by looking at the Lab of paper (i.e. a paper that is off your target white by say -2 a requires that you run your gray balance slightly green to match print to proof, something like a -2 a gray). Not sure if this is just me, or a common thing.