Ante Perkovic wrote:
[re correcting a set of photographs taken with the wrong color balance setting]
In beetween time, I took photos of the same object with camera set on "auto" and later on "M" with that bad white (more like blue) color. Photos are perfectly aligned, and the only difference is in blue hue of one of them.
Is there any way to just say to my computer: "This is good one and this is bad one. Make bad one look like good one and then do the same actions on those other pictures"?
Ante,
This problem’s been in the back of my mind for some time, and because of your question a light bulb just turned on. After a lot of thinking I think I know how to do it using the demo version of my Curvemeister plugin.
Basically the problem breaks down to this: "Here are two images. Give me a curve that turns one image into the other." For lack of a better name, I’m calling this process "curve extraction", because we would be "extracting" a curve using the data from two similar images.
The current demo version of curvemeister has enough functionality. Once you extract the curve, you may use Photoshop to do the final batch correction based on the curve calculated by curvemeister.
The curvemeister demo may be installed from:
http://www.curvemeister.com/downloads/cmdemo/index.htm Keep in mind this is still only a theoretical procedure. You may want to wait until I get the bugs out, and do a tutorial, but here’s my current thoughts on the procedure:
1) Open your correctly white balanced (reference) image in Photoshop.
2) Start the curvemeister filter (the demo version will do)
3) Select RGB mode, and click the "All" tab to show all the curves at once.
4) Alt-click the image to create a sample point at a mid tone, or something close. Use a sample size of 11×11, and pick broad areas of color, rather than areas of mixed detail.
5) Alt-click on a quarter tone and a three quarter tone
6) Add more points as necessary, making sure that none of the resulting cont rol points lie "too close" to one another on the curve. You can refine this later on in the process by removing extra points.
7) Right click on each sample point, and select the "Pin To>Current" item. You must do this once for each sample point.
8) Right click on the image, and save your sample points to a file.
9) Click Cancel.
10) Open your incorrectly balanced (target) file in Photoshop and start Curvemeister.
11) Right click on the image, and load the sample points from the file you just saved. The image should look pretty good at this point, or you may need to "tune" the curves as follows.
12) To tune the curves, look in the curve window for any kinks that indicate two curve control points (these are different from the image window’s sample points) are too close to one another, and drag off one of the offending curve control points until each channel has a relatively smooth curve. If necessary during the tuning, you may click the Reset button to restore all the curve points will come back, and you can start again.
13) When you’re happy with the image appearance, click the save button and save the curve.
To use your curve, you may hit ctrl-F for each image you want to color correct. If you have an entire folder, make an action using either curvemeister or Photoshop’s own curves operation.
Not all images may be rescuable with this procedure. In particular images taken indoors may have a blue channel that is so dark that curve extraction is not possible. This particular situation might be addressed by using Photoshop’s channel mixer to move some of the green channel into the blue before doing the curve extraction.
I’m excited about the new applications for this, and will be doing a tutorial shortly. Using curves in this way may provide a curve based alternative to the more expensive profiling packages.
—
Mike Russell
www.curvemeister.com
www.geigy.2y.net
