Photo Tips: Color Correction

This tutorial is based on information I received from the guys at the Associated Press. The AP processes over 800 photos a day using these guidelines.

 

There is a simple four-step process to getting the perfect color correction, every time, with your photos. In order for this process to work make sure you have accurately adjusted your monitor based on the adobe gamma correction application which comes with Photoshop.

 

I will demonstrate the process in Photoshop 5.5, but any version of Photoshop will work (there might be slight differences in the location of the tools.)

 

The four-step process is:

 

1. Noise

2. Levels

3. Curves

4. Hue/Saturation

 

To begin, we need an image. Lets take the image below and work on it:

 

 

Step 1:  Noise

 

Our first step is to adjust the noise. Noise is anything from artifacts from the digital camera processing to grain in film. (Artifacts are areas where the digital camera cannot get the data from the scene and it substitutes in blobs of color to fill the missing areas.) We will correct noise in LAB color mode.

 

Changing to LAB mode from RGB will not do anything to the photo. To change mode go to Image > Mode > Lab Color.

 

So what is LAB? 

LAB color isdesigned to be device independent, i.e. creating consistent color whatever the device (such as monitor, printer, computer, or scanner) used to create or output the image.

And LAB is broken down like this:

LAB color consists of a luminance or lightness component (L) and two chromatic components: the (A) component (from green to red) and the (B) component (from blue to yellow). L is the actual layer where the image resides. This layer (L) you do not want to touch since it manipulates the actual image itself. The A and B layers are the layers we want to manipulate since this will only effect an area above the photo and not the image itself. So we will not lose image quality. Like all the steps we will go through, you will not degrade the image at any point.

LAB Setup:

So let's look at the LAB setup. Open the channel toolbar, and you will see the image to the right. You can see the original image on the LAB layer, the grayscale version in the lightness layer, and the two color screens in the A and B layers. We will now adjust the A and B layers. 

First let's select the A layer. Once you select it, the other layers will deselect and you will see the A channel in your image area. If you zoom in on the image you can visibly see the noise we are going to correct.

To get rid of the noise we will start by selecting Filter>Blur>Gaussian Blur. Now adjust the blur so the image becomes just barely smooth all over. You usually will never exceed a radius of 1.0 but this varies for each photo. Then hit OK.

Repeat this for the B layer and you have successfully completed removing the noise from the image. You will notice when you select the LAB layer again that the image has not changed at all, this is because we only changed the color screens above the image.

Once we have gotten rid of the noise, we can take the image back to RGB mode. Once again remember we have not lost any image quality by switching image modes. We are ready to start the color adjustment now.

Step 2: Levels

First we go into Image>Adjust>Levels. Now let's go through what we see here. In the main RGB Channel we see the histogram below. All we are going to do is remove the non-data from the image. We will do this process in each color channel.

To remove the non-data we will slide the arrows so they come to the beginning of the histogram on each side. In this particular channel we only need to slide the right arrow over to the start of the color data.

You should repeat this step for each color channel R, G, and B as well as the main RGB channel we just did. Each channel will be different so make sure you bring each arrow to the start of the histogram on each side. Do not adjust the middle arrow.

The left arrow adjusts the shadows or blacks, the right arrow adjusts the highlights or whites, and the middle arrow controls mid-tones. Now we have completed the color information adjustments. Make sure to hit OK after completing those steps.

Step 3: Curves

Step three is curves. This step is really dependent on the gamma of your monitor. So if you did not adjust it you will need to do so for this step. This is a very arbitrary step and not an exact science, but is based on the photographer's vision of the subject at the time he/she shot the image.

Lets now go to Image>Adjust>Curves. All we want to do here is slightly increase the lightness of the photo.

Add a point in the middle of the curve and slowly pull it out. Make sure you do not move the end points of the curve in any instance.

As the picture gets lighter keep in mind the lighting in the original setting. You want to pull the lightness out just enough without over-doing it. Once you get the light quality right you are done with curves.

Curves will always be a slight adjustment to help fine tune the overall light quality. Make sure to hit OK when you are done.

So now our image is perfect right? Well, not yet. We need to do the fine color adjustments and get rid of the colors you may not even detect in the photo. The last step is the most tedious, but the most important. We are now ready to adjust the hue and saturation of the photo. If you ever think your photos have color shifts, then this is where we fix that problem.

Step 4: Hue/Saturation

So lets go to Image>Adjust>Hue/Saturation

The first thing we are going to do is over-saturate the image in the master layer. So slide the saturation arrow to the right and watch the image.

You will notice there are very hot color spots in the image. We need to identify these colors and go in and fix them. So look at the example of the saturated photo. You can see there is a great deal of red, yellow, blue, green, and cyan in the photo that sticks out.

Now lets put the saturation level back to 0 and fix the colors that need adjusting. You will notice if you click where it says "Master" in the hue/saturation toolbar you will find the following colors listed: Reds, Yellows, Greens, Cyans, Blues, and Magentas. These are all the colors of the spectrum and the colors that can be in any photo. So even though you are in RGB mode you can adjust the CMYK color fields.

Let's select the red layer. We now need to identify and reduce the red. In the hue/saturation toolbar slide the red saturation level up slightly so you can recognize the reds -- say to about 20 or so. (The amount is arbitrary, you want it enough to see the color shifts, but not too much to blow the color out of proportion.) This will show the strong red areas in the subjects face of the photo.

Now you want to slide the hue arrow either direction to balance the color shift of the red. What you are doing is swapping the red color for another red that is a lighter or darker hue depending on the direction you slide the arrow. In the case of this photo I will slide the hue to about 8. This removes the red from the subjects face and gives him a more natural skin tone.

You need to repeat this process for each color you find to be over-saturated in the photo. It won't hurt if you adjust colors that aren't over-saturated, but you don't need to. Once you complete this step for the colors you want to adjust hit OK.

If you completed each of these steps you have successfully adjusted your color image to perfection.

This technique guarantees proper color adjustment even if you do not have a calibrated monitor. Also if you wish to do any dodging or burning, make sure to use LAB mode and do the dodging and burning in the A and B channels.

All of the steps above help to retain all the information of the original scan or digital image. Once you are finished you can change to CMYK mode if the image is for print. Hopefully your photo looks like the one on the right.

Send us some of the images you worked on for this tutorial.

- Mitch Hazam