Brian - for the type of shooting you usually do, shooting a reference shot with a gray scale target is the ideal way of doing this. Get yourself a small reference target and put it in a position where it gets hit by the same light as the subject you are shooting (before, after, during the shoot). Take a shot of it.
When you bring it into post, use it to do a white balance (eyedropper tool). Use the same WB settings on your actual images and your image WB will be spot on. That's what these cards are made for an how the pros do this in their shoots where getting the WB right on do it. NB: This assumes a raw workflow.
If you open the colour panel; the three circles that you have highlighted in the screen shot and click on the White Balance tab, click the "Grey" tab and enter the correct values into the "Kelvin" and "tint" boxes by either using the sliders or typing the values in. Please note that the process assumes correct exposure, if your exposure is off a bit the WB may get skewed a bit. It did in my testing with my ColorChecker Pro.
Reference cards are relatively inexpensive and any decent photo shop should stock them. If not, you should be able to get one from any online store, Amazon, eBay, etc. Just make sure the card is actually neutral, otherwise the WB will be off.
A piece of white paper might work. The only problem with that approach is that paper is often not white as paper manufacturers often add optical bleaches into the paper and they have a blue tinge under sunlight / fluorescent light, but at least you can try it out to test the technique to see how well it works. A commercial gray card is a good way to go. Store it properly and keep it clean, otherwise you will get a faulty reading.
Note: Pushed this to the PP thread as this is a PP question.
Last edited by Manfred M; 14th April 2016 at 01:59 AM.
if there was a decent camera shop anywhere near me would I be ordering my gear from outside the country?
I have decent camera shops near me and still order outside the country. Most of the problem is that I am after specialty items that they don't stock. Things like camera lenses, batteries, filters, seamless paper, etc. they have. Gray cards they have.
If I want a specialty item, like a leveling head for my tripod, or a new Lee filter, it's a 6 week special order that I can have by the end of the week if I order from B&H. So the answer is "it depends".
Manfred's answer about how to get accurate colors is precisely what I would have suggested. However, I think you are expecting the wrong thing. There is no reason to expect the R, G, and B histograms to line up. They should only line up if the distributions of the three colors by luminance are the same, and they usually won't be. For example, if you take a photo of a scene that has dark greens and bright reds, the green histogram will have a peak at the left, while the red histogram will have a peak at the right. The histogram simply displays the distributions of pixels by brightness and color, whatever those distributions might be. The only way to see whether the histograms are what they should be is by the appearance of the image (if what you care about is just whether the results please you) or by the use of a neutral target.
For the latter, something like this, is all you need to do what Manfred suggests. It's what I use.
Just to put a slightly different spin on Dan's response.
The only way that the three histograms would line up is if the image was B&W, i.e. all three colour channels are set to the same value.
The way that the software does a WB correction is that it looks at the R, G and B values of something you tell it is a neutral gray, checks the actual readings and then adjusts all three colour channels to have the same value. This removes the colour cast in the image.
There are some behind the scenes calculations going on as well to determine which value to balance the colours to. The closer the image is to a 'correct" exposure, the more accurate the result.