G7 graybalance and images

[MC_JerryD]

We have just used the G7 methodology to achive a good gray balance for our house coated substrate running on a sheetfed press but our images have a red look to them. All the 3 color grays read and look visually neutral, but matching proof to press the images that have a fleshtone looks off. Our proofs are certified with Oris Certified Proof and check out good using GRACoL as our target.

Also on another note. On the press test where a halftone image (B&W) is printed, the black looks like it has a redish tint to it. I know the proof will look more neutral on B&W images because the A and B value will be closer to 0 than on press. It just really stood out to us. I almost thought this was our issue with the images looker redder, but there is no black in the fleshtone areas.

Thanks in advance for any comments or suggestions.

MC_JerryD

 

[gordo]

Just a few thoughts....

What are the lighting conditions under which you are viewing the proofs/presswork?
Also, have you checked the OBA content of your proofing media vs your press sheet?

best, gordon p

 

[Lukas Engqvist]

The B&W image is printed in K only or in grey balance?

 

[MC_JerryD]

Just a few thoughts....

What are the lighting conditions under which you are viewing the proofs/presswork?
Also, have you checked the OBA content of your proofing media vs your press sheet?

best, gordon p

Thanks Gordon. The light booths are about 5K. I check them about every six months. We have 3 presses and a viewing area in prepress. The other surrounding light seem to change the color of the press sheet but not the proof. You can really see it in the 3 color gray bars. When you get close to a 5K lighted area the 3 color graybars are close to gray with a slight green if the press is not running even across. Outside 5K the 3 color gray bars turn more red.

So I am guessing OBA has to do with optical brightners. How would you check the OBA content of the proof media and press sheet?

Thanks for your help.

Jerry

 

[MC_JerryD]

The B&W image is printed in K only or in grey balance?

It is in black. I am using the GrayRails 05 that is in the GRACoL press test. The image that has a 4 color, 3 color and black only image. The 3 color image looks better then the black only.

Jerry

 

[Lukas Engqvist]

Hmm, did you check the Lab values of the black? Maybe you need to look at your options. Some manufacturers have a warm (reddish) and a cool (blue cast) black, who knows there may be other blacks available too.

 

[gordo]

Thanks Gordon. The light booths are about 5K. I check them about every six months. We have 3 presses and a viewing area in prepress. The other surrounding light seem to change the color of the press sheet but not the proof. You can really see it in the 3 color gray bars. When you get close to a 5K lighted area the 3 color graybars are close to gray with a slight green if the press is not running even across. Outside 5K the 3 color gray bars turn more red.

So I am guessing OBA has to do with optical brightners. How would you check the OBA content of the proof media and press sheet?

The color shift could be caused by optical brightners - i.e. the press sheet contains them but the proof paper does not. Or it could be caused by metameric failure.

RE: OBAs. A simple inexpensive way to visually check OBA content of the paper is with a fluorescent black light:

Compare your proof paper with your press paper under white and black light:

The better they align under white and black light the less problems related to OBAs that you'll have.

More info on this topic here: Quality In Print: Optical Brightners

RE: Metameric failure:
A chromatic 3/C grey (50C, 39M, 39Y) and an achromatic 50% black form a metameric pair. What this means is that they may match color under one lighting condition, however, under a different lighting the 3/C grey will shift hue because it is spectrally different than the 50% black. This mismatch due to lighting conditions can be exacerbated between inkjet proofs where the 50% black patch may be made up of 4/C and presswork where the 50% K is only made up of black ink.

More info on metamerism here: Quality In Print: The issue of metamerism in print production

More info on the issues of grey balance here:
Part 1: Quality In Print: Grey Balance Unbalanced – An inconvenient truth, part 1 of 2

Part 2: Quality In Print: Grey Balance Unbalanced – An inconvenient truth, part 2 of 2

best Gordon P

 

[Dan DeSimoni]

Trap

Trap

Even though the press was gray balanced did you achieve a good tolerance on your primary colors and secondary trap colors ?

 

[Hanson]

I can't visit the link which you mentioned, did u have another link

I can't visit the link which you mentioned, did u have another link

The color shift could be caused by optical brightners - i.e. the press sheet contains them but the proof paper does not. Or it could be caused by metameric failure.

RE: OBAs. A simple inexpensive way to visually check OBA content of the paper is with a fluorescent black light:

Compare your proof paper with your press paper under white and black light:

The better they align under white and black light the less problems related to OBAs that you'll have.

More info on this topic here: Quality In Print: Optical Brightners

RE: Metameric failure:
A chromatic 3/C grey (50C, 39M, 39Y) and an achromatic 50% black form a metameric pair. What this means is that they may match color under one lighting condition, however, under a different lighting the 3/C grey will shift hue because it is spectrally different than the 50% black. This mismatch due to lighting conditions can be exacerbated between inkjet proofs where the 50% black patch may be made up of 4/C and presswork where the 50% K is only made up of black ink.

More info on metamerism here: Quality In Print: The issue of metamerism in print production

More info on the issues of grey balance here:
Part 1: Quality In Print: Grey Balance Unbalanced – An inconvenient truth, part 1 of 2

Part 2: Quality In Print: Grey Balance Unbalanced – An inconvenient truth, part 2 of 2

best Gordon P

Hi Gordon,

Could you send another link for my reference,cause I can't visit your link which mentioned in this post

 

[gordo]

Hi Gordon,
Could you send another link for my reference,cause I can't visit your link which mentioned in this post

Note: I've added a space after http: so that the url won't hot link - you'll have to cut and paste.

More info on this topic here: http: //qualityinprint.blogspot.com/search/label/Optical%20Brightners

RE: Metameric failure:
A chromatic 3/C grey (50C, 39M, 39Y) and an achromatic 50% black form a metameric pair. What this means is that they may match color under one lighting condition, however, under a different lighting the 3/C grey will shift hue because it is spectrally different than the 50% black. This mismatch due to lighting conditions can be exacerbated between inkjet proofs where the 50% black patch may be made up of 4/C and presswork where the 50% K is only made up of black ink.

More info on metamerism here: http: //qualityinprint.blogspot.com/2010/05/issue-of-metamerism-in-print-production.html

More info on the issues of grey balance here:
Part 1: http: //qualityinprint.blogspot.com/2009/05/gray-balance-unbalanced-inconvenient.html

Part 2: http: //qualityinprint.blogspot.com/2009/05/gray-balance-unbalanced-inconvenient_14.html

best Gordon P

 

[Bloodsaler]

The difference mainly caused by the Light ot the OBA?Does something affect by the ink part?

 

[MC_JerryD]

Even though the press was gray balanced did you achieve a good tolerance on your primary colors and secondary trap colors ?

Yes, I started with being sure my primary and secondary colors were within a dE 5 tolerance. In fact I am a little below a dE of 3.

Also, after another press run test. If we achieve a good gray balance our images to do not match our proof. I am using ORIS Color Tuner to output our proofs and ORIS Certified proof to be sure they are within a GRACoL standard. When we match the images, the grays turn green. I know we are not selling gray, but seems like we should not be as green as what I am seeing and reading on my GrayFinder chart. Plus I am concerned about my process builds.

JerryD'

 

[Mike Strickler]

Some Additional Thoughts

Some Additional Thoughts

The lighting can certainly be an issue, but I would also look carefully at the numbers. A "good" proof or press sheet may vary from the ideal on certain colors to a noticeable degree, and flesh colors are quite critical. Run a test form on the proofer and press that contains extra patches of flesh colors and measure these as well--or run an entire IT8.7/4 and compare the measured result with the characterization data set (e.g., in Measure Tool). What is the color of the press substrate? Could it be a tad pink? Is it perhaps the case that your proof paper has a slightly bluish or cyan cast and the proof was made with relative colorimetric rendering? The sad fact is that lighting is never perfect and metamerism issues never completely absent, so it's important to isolate that problem by looking at the actual measurements on the sheet.

 

[Lukas Engqvist]

Just being in dE 3 isn't everything. I is quite possible to be mathimatically correct but visually not. When you chart your target and actual results in a spider diagram, and compare with your grey shift do you see any correlation?
(If you are experiencing a reddish cast and your magenta is +dE 3 and your cyan -dE 3 then that would suggest either lowering magenta or increasing cyan)