How do I gray balance in Photoshop?

[overtwo]

I've been coming across this quite a bit now on different websites telling me to make sure my grays are balanced in Photoshop before ripping? What does that mean and how do I go about it?

 

[meddington]

Re: How do I gray balance in Photoshop?

Not really a topic for a real quick answer but I'm short on time (T-Day Looming), so here goes...

Best/more ituitively done in RGB. Use an RGB working space like ECIRGB or Adobe RGB. In each image, look for known grays or near gray/white to balance towards equal RGB values using levels/curves. Convert to a CMYK ICC profile with standardized gray balance triplets (50C, 50MY) like the recently released Gracol and SWOP profiles. If you working with CMYK files already, you can either twist CMYK curves toward CMY gray balance triplets or convert to RGB and proceed like above.

Now, that's one answer (a very sparse one at that) and you're sure to get other opinions.

 

[disbellj]

Re: How do I gray balance in Photoshop?

Michael meant 50C 40M 40Y, which is the gray balance built in GRACoL and SWOP. So an RGB where all three values are equal should convert to a balanced gray, not casted. For instance, if I have a 50% gray in RGB (127,127,127). If I go to Info palette and set my Second Color Readout to Lab Color, my Lab numbers read Lab 54,0,0. If I then convert to GRACoL2006_Coated1v2, I get CMYK 50,41,41,14. If I then go to color settings and set intent to Absolute Colorimetric (so I can see printed Lab values), my Lab numbers read Lab 51,0,-1. We can see that the color is gray balanced because the a* and b* are both 0 +/- 2. We also see that the L* value is a little lower, which means the gray is a little darker when printed. This can be shown by soft-proofing the RGB (going to View > Proof Setup > Custom, and choosing GRACoL2006_Coated1v2 as profile if it is installed in the system, Relative Colorimetric Intent, Black Point Compensation checked, Simulate Paper Color checked, Simulate Black Ink checked. Just turn on and off preview to see it get darker).

We could get the gray to be the same printed Lab values as what we see in RGB when color settings are set to Relative Colorimetric Intent (Lab 54,0,0). To do this, we would have to manually convert from RGB to GRACoL2006_Coated1v2 (Edit > Convert to Profile) with Absolute Colorimetric Intent. If color settings is then set to Absolute Colorimetric Intent, then the Info palette will show printed Lab values. We see that when converted to CMYK this way that the resulting Lab values (printed values) are 54,0,0, so it didn't get darker in this case, but looked the exact same as the RGB gray, although the CMYK to do it is 48,39,41,11.

Both are gray balanced, but one is the exact same gray and one is a little darker.

Theoretically, we would use Absolute Colorimetric Intent for all conversions. Unfortunately, we can't use Absolute Colorimetric Intent for conversions of production files going to plate/press because it takes the paper of the source (white) and adds dots on paper in the destination. Do the tests above over, except make half the Photoshop document filled with white (RGB 255,255,255) and convert using the two rendering intents. See how the one converted with Relative Colorimetric Intent has the destination CMYK white as 0,0,0,0? See how the one converted with Absolute Colorimetric Intent has the destination CMYK white as 0,0,2,0? We don't want a dot printing there where it should be just paper, so we are really stuck using Relative Colorimetric Intent for our conversions because of this, and only using Absolute Colorimetric Intent for proofing (or for tests like the ones above, where I want to see the printed "appearance" - described in Lab).

Hope this helps.

Don

 

[overtwo]

Re: How do I gray balance in Photoshop?

Wow! That does help! Thank you very much. I'll start looking into that as soon as I get a minute.