Masking and Darkening to Remove Red Eye
I'm going to show you how to correct red eye by making a mask and using the brightness curve command. These topics are covered in Case 1 in more detail if you need to brush up a bit. Photoshop, Paint Shop Pro, and other similar programs will have similar functions available. It takes me between 1-2 minutes to correct red eye using this procedure. I can usually use the automatic correction faster, but I've been happier with the results using the following method.
First, I make a mask (using the Mask Command - see Case 1 also) over the pupils. To do this, I zoom in on the pupils until I can see individual pixels. The screen shot below shows the start of the process.
I have zoomed in so the photo is enlarged 5:1. You can clearly see the reflection from the flash, and you can see the individual pixels. I'm using the paint brush to paint in the mask, starting with a small radius brush with a high softness (i.e. 100% fill in the center of the brush, with gradually less coverage extending out to the edges of the brush). This lets me trace the edge of the pupil, and the softness will let there be a small transition zone between very dark and very light, so it prevents an unnaturally abrupt change (we'll use feathering in a moment for the same reason). Progressing onward:
Once I trace the edges carefully, I use a larger brush (radius of 6 in this case) with softness set to 0 to fill in between the edges. When I've masked in both pupils, I use the Feather command, with a 2 pixel radius - this command gives a gradual transition from completely masked to completely unmasked in the radius selected, and helps provide a more gradual transition when I darken down the pupils. The feathering radius is small, because there is a reasonably sharp dividing line between light and dark when looking at a pupil, but a small amount of feathering makes it look more natural (IMHO). The screen shot above shows both pupils filled in, and the feathering applied.
Next, we apply the Brightness Curve command:
The left image is the original, and the right is the preview image for the changes from the brightness curve. In this case, I used the curve function instead of the histogram function on the brightness curve command (as opposed to Cases 1 and 2), as I was making a reasonably simple transformation and did not need to see the impact on the histogram. This version is very close to the Photoshop Curves command (you would do it for "RGB" instead of brightness, but it accomplishes the exact same thing). The graph shows the the original image brightness levels along the bottom with a histogram of the pictures brightness levels. The left hand side shows the modified brightness levels, and the curve shows how the original brightness levels are modified into the new image. If the curve were a straight line at a 45 degree angle (which you can see faintly as one of the lines in the "X" on the graph, the one going from the lower left hand corner to the upper right hand corner), then the new image would be exactly like the old one. I put a control point (little black circle, equivalent to the control points we used in the histogram function) on the curve by shift-clicking, and then dragged the circle down. This curve means that pure white levels (right hand side of the lower axis) stay pure white, but anything less than pure white gets much darker. You can see the arrows in the middle of both scales pointing to the control point. What is a very light gray in the original (bottom scale) becomes a very dark gray in the modified image (left side scale).
Also note the amount slider, which is set for 100% effect to the masked area (white slider), and 0% to the unmasked area (black slider). This means that the curve will only be applied to the area that I masked.
Why did I do it this way? Two reasons, first, doing the curve like this maintains the bright flash reflection (on the cat's right pupil above, you can actually see two reflections, but the brighter one is the flash). The photo would look wrong if the flash reflection were not there (which I'll show you). Second, doing it this way leaves a little bit of the color, which I think gives a much more natural look. Look at the finished product below (I also did just a bit of color balancing, and sharpened the photo using unsharp mask).
The pupils look much better, but the rest of the photo is unaffected.
On the next page, I give a few more comments on the process.