Color matching color charts in multiple images

[flea77]

I have quite a few images shot with an Xrite Color Checker Classic under different lighting conditions and I want to match the color charts in each one so that other items in the images show actual differences. In other words, if the color charts are all identical in all images, any other objects will actually show if they are redder than each other etc.

I start off with all the images in Lightroom 4 and they look wildly different. I go into the development module and select the eyedropper under custom white balance and select the medium gray box, third from the left on the bottom row of the color chart. For conversations sake we will say I do this to image001 taken in direct sunlight, and image002 taken in heavy shade. This gets them to look very close to the same.

I then open them both in Photoshop CS5 and notice that you can click on 30 different places in the top left (medium brown) color chart box and get 30 fairly broadly different results, so I apply a 20 pixel gausian blur to even things out. Now I select a sample from image001 of that blurred box and get vaules of 128,80,58 and then from image002 selecting the same box I get 117,70,50. Interesting.

Now I adjust the brightness of image002 so that when I sample the top left box I get values of 128, 77, 55. Much closer although I would prefer it to be even closer.

That's OK though, lets look at the teal box in the upper right of the image. Sampling of image001 gives me 129,192,183, and then a sample from image002 give me values of 139,204,192. Again, close but I would really like closer.

So I guess my question is this: The neutral white balance tool in Lightroom gets me fairly close with one click, but then each image has to be loaded in Photoshop and manually have the brightness adjusted until the colors fall in line with each other. Is there a simpler way, or a more accurate way, or both, that will allow me to have as close as possible matches between the color charts on both images.

This is for a scientific comparison project so yes, it needs to be as exact as is possible.

Thanks for any ideas.

Allan

 

[Garbz]

Firstly you don't need to blur the image. The eyedropper tool has an option for selecting an x by x average sample instead of a point sample.

Secondly light isn't just a certain colour it has a certain spectrum. Directly sunlight approximates a black body radiator quite well, so do incandescent lightbulbs. Shade and clouds however have all sorts of weird effects that change not only the colour temperature the radiance of different colours depending on their spectrum.

 

[KmH]

So I guess my question is this:......... Is there a simpler way, or a more accurate way, or both, that will allow me to have as close as possible matches between the color charts on both images.

Yes, there is a simpler and more accurate way.

Use the Xrite Color Checker to set a custom white balance in the camera each time the lighting changes when you are out shooting.

Note that if you use mixed lighting you can forget accurate.

 

[flea77]

Garbz,

Thanks! I never knew the color picker had that feature, that is really helpful!

Yeah, I am not really trying to get so picky as to be identifying the spectral elements of a G class star, as I did here:

However getting as close as is reasonably possible for the images I have is important.

KMH,

My problem is the lighting conditions are rapidly changing. It isnt mixed lighting really (I understand mixed lighting as shooting strobes, fluorescent and/or mercury in some combination, for example) but it could be in the shade one minute (behind a building), in full sun the next, and in partial shade due to clouds the next.

It sounds like what I am doing is going to have to be done the way I am, oh well, it never hurts to ask and I learned something from it so it was a good day!

Allan

 

[LusiJohn]

You can refer to Koolchart to fix this issue. Even you can add 2D and 3D effects to your chart color.