I'm not a graphic artist so the idea of automatic color correction really appealed to me.
Since I didn't have the mad skills needed for manual color correction, I wanted to find out which program was best at correcting color automatically. So I ran a bunch of tests on various programs that have automatic color correction features. The results of my comprehensive testing are on the Color Correction Software page. I briefly explain how to use each program below.
Converting to a Standard Color Space
First things first! Before correcting color or adjusting levels, I recommend converting device-specific color spaces (such as scanner color space profiles) into a common working color space. For color scans (of color or grayscale prints), I suggest using "sRGB" which is the most common working color space for color images. For grayscale scans, I suggest using "Gray Gamma 2.2" which is the most common color space for grayscale images.
For Color Scans
If your image already has an sRGB profile attached, you can skip this step.
If your image has no profile or has an "EPSON sRGB" profile attached, it's a simple matter to convert the image and profile into standard sRGB. Simply open the file into Photoshop and select "Convert to sRGB Profile" in the "Convert Color Profile" menu item under the Image menu. The conversion is instantaneous and there is no feedback. You should notice virtually no change at all to the image. The only change you'll notice is later when you save the file. The "save as" dialog box will have a checkbox labeled "Embed Color Profile: sRGB IEC 61966-2.1" which should be checked.
For Grayscale Scans
If your image has no profile attached, it's simple to attach a standard grayscale profile. When saving your file in Photoshop, make sure the checkbox labeled "Embed Color Profile: Gray Gamma 2.2" is checked.
Using the Levels Tool
Even if you use automatic color correction, it's good to learn about levels and histograms. There is a four part article about levels and a two part article about histograms by Ron Bigelow on ronbigelow.com that are very educational. There's also a good book or two mentioned in Books link.
Levels are adjusted using Adobe® Photoshop® Levels Tool, which is shown to the left. To display this tool, select Adjust Lighting - Levels in the Enhance menu. A quick guide to using the Levels Tool follows.
Remember that you can always check for clipped pixels by option-clicking the left Input slider (black point) or right Input slider (white point).
Channel: Normally RGB. If you are using the midpoint slider to remove a color cast, this can be red, green, or blue.
Output Levels: Sliders in the Output Levels can be adjusted to lighten dark shadows or darken bright highlights. The left slider affects the darkest tones. Slide it to the right until you can see some detail in the darkest shadows. The right slider affects the lightest tones. Slide it to the left until the whitest highlights are no longer dazzling.
Input Levels - Midpoint Slider: This slider is used if the overall look of an image is too bright or dark. It's similar to adjusting the brightness on a television. If the Channel is set to a specific color (such as red or green), this slider can help remove color casts.
Input Levels - Black Point & White Point Sliders: These sliders can be used if a midpoint adjustment isn't enough to fix the levels. They can darken shadows and brighten highlights (the opposite of Output Level sliders). This has the effect of increasing the contrast.
Correcting Color Manually
Learning how to manually correct color is as difficult to explain as it is to learn. So I shall refrain. I can, however, offer suggestions as to which programs are helpful. I provide links and explain these programs in more detail in the Color Correction Software section of this website.
A few articles on Adobe.com that may be of help:
- Photoshop® Elements is great, but some tools don't work with 48-bit color images.
- Photoshop® CS/CC has more features and works fine at any depth, but it's more expensive.
- PictoColor iCorrect OneClick is an Elements plugin for removing color casts.
- Adobe® Lightroom® has an outstanding interface
and extensive manual color correction features.
- Other image editors are listed in the Repair Damaged Photos section.
Correcting Color with PictoColor iCorrect OneClick
To use OneClick, you simply click on objects that should be a shade of gray (or white) in an image. Things that should be a shade of gray include whites of eyes, gray suit, black shoes, galvanized pole, white trim, etc. Finding an object that should be a shade of gray can be difficult when everything has a haze on it caused by a color cast. If you click on something that should not be some shade of gray, colors will change weirdly. On the other hand, if you click on something that should be a shade of gray, colors will instantly become much more normal.
I have found making big adjustments with OneClick's Enhancements can cause clipping issues. After using OneClick, you may wish to check for a well-formed histogram without clipping. If clipping occurs, you may want to undo and try again.
Correcting Color Automatically with Photoshop Elements
Photoshop has two automatic color correction functions. One is called Auto Color Correction and the other is called Auto Levels.
On most photos, Auto Color works great to correct the color balance without having to use Auto Levels. If the colors in the photo have shifted badly enough to cause a strong color cast and hazy look to the photo, you may need to perform an Auto Levels before using Auto Color. In rare cases, Auto Levels can fix the photo completely without needing to do an Auto Color.
While Auto Color is extremely easy to use and can work wonders on severely faded photos, I have noticed some images have turned out a tad dark or contrasty. This is often easily fixed with Photoshop's Level tool. The black point and white point sliders in the Output Levels and the midtone slider in the Input Levels can be adjusted as needed.
Correcting Color Automatically During the Scan
With Canon ScanGear, Epson Scan, and VueScan, you can scan and correct for color at the same time. You just need to make some extra settings which are explained in the Scan step. The color correction will happen during the scan, although some tweaks will have to be made after the scan. See below for tweaks.
Making Tweaks after Automatic Color Correction
Although automatic color correction works pretty well, there will often be a slight color cast (overall tint) that needs to be removed. If the photo is faded, you may need to bump up the saturation. If the overall contrast is weak, it can easily be increased. And if the shadows are too dark, or the highlights too bright, or the midtone contrast needs a tweak, there are adjustments for those things as well.
Removing Color Casts
Color casts may remain after any kind of automatic color correction. The way I usually remove casts is to use the ever-popular Level dialog box. Select a Channel color (other than RGB) at the top of the dialog box, then use the middle Input slider (aka midpoint). There are three primary colors to choose from. I usually start with the color that has the strongest cast. Since green is very noticeable and is easily visible on faces, I often start with green.
To remove a green cast from an image, select the green Channel in the Levels dialog. Then adjust the midpoint slider one way or the other to remove the cast. If you remove too much green, the image will start to look purplish. Finding the right place to move the midpoint to takes some trial and error. The midpoint is adjusted correctly once there is no green or purplish tint.
Even after fixing one color channel, it is likely that other color channels need to be fixed as well. Subtle casts may not be apparent until adjusting the midpoint of each color channel. Trying various minor midpoint adjustments while turning Preview on and off a number of times for each adjustment makes subtle casts more apparent. Try to find a midpoint adjustment that makes whites look cleanest and colors most true to the eye.
Making Other Tweaks
If the image has weak color overall, you can increase the saturation. If only a certain color is weak, you can increase the saturation for that particular color. I have found saturation usually does not need adjusting except for extremely faded photos (such as the one in the example below).
If the contrast is weak, the black point and/or white point sliders in the Input Levels can be adjusted. If these are already set correctly, you can use the shadows/highlights tool in Photoshop to increase the midtone contrast.
If adjusting the black and white points in the Input Levels doesn't increase enough details in dark shadows or bright highlights, you can try the shadows/highlights tool in Photoshop. Using Lighten Shadows or Darken Highlights with this tool can bring out more detail. The results can either look great or artificial, depending on the photo.
Color Correction Example
Here's an example of a faded photo and what happens when it is color corrected. Manual correction can be incredibly tedious and time-consuming for extremely faded photos. Automatic correction is quick, but tweaks (quick adjustments) are still needed afterwards. The results after adjustments are very similar among the three images shown below.
Just below is the uncorrected (straight) scan. It looks just like the print that it was made from! From the histogram, you can see how the colors have shifted. This has given a slight yellowish cast to the entire photo.
In the first row below are the results from Epson Scan and Photoshop Elements. These are before any adjustments. |
In the row below that are the results from the following adjustments to each image. Unless otherwise noted, all black point, white point, and midpoint adjustments below are made with Input Sliders in the Levels Tool.
To enlarge these images, simply widen this window.
- For Epson's straight scan, the black and white points for the three color channels were adjusted to align with each other. More specifically, the green channel's black point was moved to the left while the green and blue channel's white points were moved to the right. This still left a slight yellowish cast, so the blue channel midpoint was adjusted to remove it. Finally, the black point was lowered to darken the bright shadows.
- For Epson's color corrected scan, the black point was slightly lowered to darken the bright shadows.
- For Photoshop Elements's automatically corrected image (of an Epson straight scan), the dark shadows were lightened by sliding the black Output Slider to the right.
Epson straight scan
exp = 2
Epson corrected scan
exp = 2, restoration = on
PS Elements auto-correction
Auto Levels + Auto Color
Epson straight scan ++
green ch. black point = 10
green ch. white point = 244
blue ch. white point = 204
blue ch. midpoint = 1.05
black point = 10
Epson corrected scan ++
black point = 5
PS Elements auto-correction ++
black output slider = 10
Many paths lead to the same destination. So pick the easiest :-)