Introduction: Intermediate Photoshop - Correcting Color Shifts

Picture of Intermediate Photoshop - Correcting Color Shifts
I'm sure a lot of us have come across color shifts in our photography, and they can be extremely frustrating.  This instructable is going to quickly go over why the shifts are there in the first place and then how to fix it in post. 

This method can be a little complicated, so take your time and try to practice, it will probably take a few tries to get it down.

You will need:
  • Photoshop (or similar editing program)

**NOTE: All photographs used in this tutorial were shot and retouched by myself

Step 1: Why Does My Photo Have a Color Shift?

Picture of Why Does My Photo Have a Color Shift?

First of all, before we get into correcting color shifts, we have to understand them.  Most cameras these days have an automatic white balance setting to control this issue, but everyonce in a while it can be inaccurate.

Color shifts are caused by different color temperatures in light, we call these "Kelvin temperatures."  Daylight has a Kelvin temperature of 5000, and is the most neutral you can get your photo to look. 

Have you ever photographed something in your house under a typical house bulb and the whole photo turned out orange or yellow?  That's because typical household lights have a Kelvin temperature of about 3000, which can look yellow, but because the human brain is so sophistocated, it corrects this to daylight temperature for us.  Tungsten and flourescent light bulbs can also have a similar effect, where we don't see the shift, but our cameras do.

Tungsten bulbs tend to have a magenta shift to them, while fourescent bulbs can turn a photograph green.  Yuck! 

Step 2: Correcting the Issue

Picture of Correcting the Issue

In order to correct the color shift, we need to adjust both the highlights and the shadows in the image, as they both have their own separate temperatures.

First, you're going to need the Information tab open near your layers and adjustments palettes.  Click on the icon and you will see it pop up on the right side of the screen.

Select the Eyedropper tool from the tools palette, choose a highlight on your subject's face, (make sure it's not in an eyebrow or something with a lot of detail), and shift click that spot.  This will create an anchor point on your image that you can draw information from to fix whatever color it is that's out of order.  Do this again in a shadow area.  When you set the points, did you notice two new RGB menus show up in your info palette?

If you don't like where you put the point you can always remove them by holding shift + opt, (shift + alt on a PC), and click on the anchor. 

Step 3: Correcting the Issue - Continued

Picture of Correcting the Issue - Continued

Once you have your points selected, you need to change the RGB menus in your info palette to CMYK menus, as this will be much easier to get the right correction.  Next to the list of percentages for RGB, there is an eyedropper icon.  Click the icon and scroll down to where it says CMYK color.

R - Red
G - Green
B - Blue

C - Cyan
M - Magenta
Y - Yellow
K - Black

Now we can use a "skin recepie" to find out which colors are off so we can adjust them in curves.

Step 4: Skin Recepies

Picture of Skin Recepies
Now, here comes the slightly complicated part: the skin recepies.  Light, medium, dark and very dark skin tones are going to have different number combinations to bring them back to their natural state.  Below is a list of these combinations for each type of skin, (the ratios of these numbers are the same for the highlights, however the numbers may be a little bit lower).

Light
  • C : 1/5 - 1/3 of M and Y 
  • M : teens - lower twenties
  • Y : teens - lower twenties
  • K : none

Medium
  • C : 1/5 - 1/3 of M and Y
  • M : mid-twenties - lower thirties
  • Y : mid-twenties - lower thirties
  • K : none

Dark
  • C : 1/3 of M and Y
  • M : mid-thirties - lower forties
  • Y : mid-thirties - lower forties
  • K : none

Very Dark
  • C : 1/3 of M and Y
  • M : mid-forties - mid-fifties
  • Y : mid-forties - mid-fifties
  • K : 1 - 5%

Looking at these skin recepies and looking at your info palette, do you notice any particular number that is standing out from the others or where it's supposed to be?  That is the number we need to fix. In this particular photograph it looks like the magenta curve needs some help.

Go to your adjustment palette and select the "Curves" icon, this will bring up a curves adjustment layer.  Once you have that open, go to the curve that needs the most help.  In this case, we are going to go to the green curve as the opposite of green in the color wheel, (according to light, not paint), is magenta.  


*Tip: In curves, there is an overall RGB curve, which will adjust the brightness, a red curve, which adjusts red and cyan, a green curve, which adjusts green and magenta, and a blue curve, which adjusts blue and yellow.

In order to make sure we are adjusting the correct part of the curve, cmd + shift click, (ctrl + shift click on a PC), your anchor point on the photograph and a dot will appear on all three channels of the curves layer.  This is where we need to adjust our curve.

Step 5: Adjusting in Curves

Picture of Adjusting in Curves

First we are going to adjust the highlights.  As I mentioned before, in this photograph, I needed to adjust the magenta, so I went to the green layer and pulled the curve until both the magenta and yellow were at 7% and the cyan was at 5%, (remember, I am only adjusting the green curve, the other numbers will move on their own with your curve, so keep an eye on them).

Looks much better already doesn't it?

Lets move on to the shadows.

Step 6: Adjusting in Curves - Continued

Picture of Adjusting in Curves - Continued

It looks like the shadows need a little more help on this photograph so we'll have to adjust two curves layers.  Just as we did with the highlights, cmd + shift click your anchor point to get the dot on the curve.  I first adjusted the green curve as I did before, but in doing this, it affected the cyan curve, so after getting them as close as I could, (sometimes they don't exactly match, but don't worry about that, just get them as close as you can), I went to the red curve and adjusted it to get the skin recepie ratios back.

Ta da!

Now of course, not all photos are the same, this one was relatively easy to fix, so don't loose hope if you're having issues, just keep at it!  Practice makes perfect!

Comments

bowlofnoodle (author)2012-12-06

Make a video please.

fozzy13 (author)2012-11-16

I have this problem all the time with my Instructables pictures!! If I don't get the perfect shot, everything gets washed yellow.
This would be awesome as a GIMP tutorial though.. so that I can do it ; )

jimvandamme (author)fozzy132012-11-21

Try Colors-> Auto -> Color correction. Or Colors -> Color Balance -> slide the different sliders until you get what you want. I duplicated the sample picture correction by sliding the magenta to green a bit.

fozzy13 (author)jimvandamme2012-11-23

Awesome. Thanks for the help!! : )

jimvandamme (author)jimvandamme2012-11-21

There are also a lot of Gimp tutorials all over the web, and youtube videos.

I wish I could help you with that. :/ I'm very unfamiliar with GIMP. In fact, I had never heard of it until I joined this site.

kmpres (author)2012-11-19

Awesome instructible, thanks for sharing. I've often wondered how this black art worked. I have a question: Is it possible to derive a color photograph from a black and white one without "painting" pixels directly (colorizing)? It seems to me that color shifted photos look almost black and white so the steps ought to be similar. I have some pictures taken in the first half of the last century and would dearly like to see them in color without actually "colorizing" them. Is there software that can do this?

KathyTackettPhoto (author)kmpres2012-11-19

Unfortunately, no there isn't. :( If you were trying to turn a black and white photograph into a colored one without painting the individual colors in, the end result would be very monotone. instead of having, say the flower in the photograph be red, the whole image would be red.

ndr1968 (author)2012-11-18

Needs about "plus 5" red. One on the right has a cyan cast to it.

Light_Lab (author)ndr19682012-11-18

On my screen it looks a bit greenish. That's the problem, there was a time when we nailed the colour to a print on paper and the colour balance is different as AnubisAndIsis says below.
Now we mostly look at pictures via LCD screens and the colours differ from monitor to monitor.
Here in the lab we calibrate our monitors with an i1 from Gretag MacBeth and keep libraries of ICC profiles. I also use special software to colour correct and for KathyTackettPhoto's test image I get quite a different result. BUT....despite the science I would actually warm the colours a little in the final "perfect" result.
Photography is still an art, the photographer knows what sort of effect they want to get. Even if exact realism is required the photographer was there and knows what is real. Ultimately they produce the result they want to depict in the display technology they have at hand.
It is always a good idea to calibrate your monitor and keep the ICC profile backed up.

Light_Lab (author)Light_Lab2012-11-18

Sorry about the duplicated image - some bug in the upload would not let me delete the copy.

triumphman (author)2012-11-15

I love that door! Looks like one I saw when I was in Switzerland! Thanks for bringing it back to my memory!

It's the front door of my friend's house! It's 400 years old!

AnubisAndIsis (author)2012-11-16

A better approach is to check your endpoints first, then move curves only if there is a need to adjust tones. Changes in curves of any kind affect tones, which affects contrast, which you can see in your end result - although you've balanced the color, there is a loss in contrast in many of your three-quarter and quarter-tones. For offset printing, to avoid posterizing at the last printable dot, set the white points to around 1% MYK 2-3%C, and blacks from 80-90% CMY and 95% K, depending on your gray replacement and/or under color removal model. The C shift is required due to the natural inclination to perceive "bluish" as balanced, perfectly balanced numbers look reddish and muddy (and works better due to color contamination as a result of the limitations of printing pigments.)

You can then locate the 50% tonal areas and just note the balance - after adjusting the endpoints it should be fairly balanced. If not, use the hue/saturation tools to MOVE the colors, not bend the tonal curves.

The above is for optimum offset printing specs, you'd handle it similarly with RGB.

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