How does a color chart work?

I've noticed people taking test photos of subjects holding a color chart and then assume they use the chart somehow in post processing. Was curious how it works? How do you use the color chart in your pp?

Being able to refer to "known" colours should help getting accurate colour reproduction in post-processing.

I'm not an expert, but recently my wife was asked to photograph lots of different fabrics for a customer. I printed out a 7- or 8-step gray bar on our cheapy black-and-white laser printer, and asked her to make sure that it was visible in each shot (or at least in the first of each set of shots). Then, when she gave me the card full of images to process, it was so easy just to use the black, white and gray eyedroppers on the gray bar, and bam! the colours were perfect.

That's a fairly simple example, but it worked a treat. I believe it's also very good practice for photographing artwork.

It goes a little deeper though:

For commercial printing, clients don't want a close match, they want an exact match.
White must be 255, 255, 255 .. Black must be 0, 0, 0 .. Red must be 255, 0, 0 etc...

Using a calibrated color chart, when you eyedropper Red and it comes back electronically as 248, 1, 2 , it will look Red but you know for sure it isn't exactly correct and needs tweaked.

It can take a lot of the guesswork out of White Balance and Saturation issues.

FlyingPhotog wrote in post #6242018
It goes a little deeper though:

For commercial printing, clients don't want a close match, they want an exact match.
White must be 255, 255, 255 .. Black must be 0, 0, 0 .. Red must be 255, 0, 0 etc...

Using a calibrated color chart, when you eyedropper Red and it comes back electronically as 248, 1, 2 , it will look Red but you know for sure it isn't exactly correct and needs tweaked.

It can take a lot of the guesswork out of White Balance and Saturation issues.

That makes sense. How would you go about tweaking the color in pp if say your red, etc.. was off a bit?

RyanM wrote in post #6243266
That makes sense. How would you go about tweaking the color in pp if say your red, etc.. was off a bit?

There's probably a faster and simpler way (I'm far from a PS expert) but I'd do it this way:

- Select the area you want to adjust (Lasso just a small area or choose all the reds via a Color Selection)
- Promote it to a new layer and create a mask
- CTL + Click the mask box for that layer
- Click on the picture portion for that layer
- Tweak just RED as an adjustment layer

Selective Color might work, too.
It wouldn't hurt to be sure that your monitor is calibrated, your browser is color managed, & Photo$hop is properly set up. Or you could tell your commercial printer that, "This should be red", & let him fix it.