So there seem to be tons of ways to get the redeye out and this is a related question.
Is there a way to “turn down” the brightest pixels of a specific channel? As in could I convert all red pixel values greater than 200 to be equal to 200? Or do the equivalvent of subtracting 50 from the red value of all pixels with red greater than 200?
Does that make sense?
PC
Disclaimer: I’m no Photoshop expert, and if someone else tells you there’s a better way, then you’re probably better off listening to them.
Not sure if this is exactly what you want, but i think you can do it in Levels.[ul]
[li]go to Image > Adjustment > Levels[/li][li]when the Levels control comes up, choose the Red channel from the drop-down menu at the top[/li][li]move the Output Levels slider at the bottom of the panel to 200. This will change the red channel output so that there is no red output over 200.[/ul][/li]
Now, of course, this will not just affect colours that appear red, but will affect the red balance of all the colours in the image.
Is this the sort of thing you were after, or have i misunderstood your question?
(BTW, for more flexible results, do the same thing but, instead of doing it in Image, do it in Layer > New Adjustment Layer > Levels)
Hmm… correct me if I’m wrong, but I think that would only work if your image consisted entirely of pure shades of red (and no other colors). Meaning, you don’t have any white, green, yellow, blue, pink, etc. areas in your image (i.e. the blue and green channels aren’t used at all).
If you simply tone down the red across the board, all your white areas will turn cyan due to the lack of red.
If this is a redeye question, I think what you want to do is select all pixels with a red value greater than 200 AND blue and green values less than X (maybe 100?). You only want pixels that end up looking red, not all pixels that contain a high amount of red (because white and other colors would be included as well).
The easiest way to do that, I think, would be to use either the Magic Wand tool or the Select Color Range function to select the colors similar to one redeye. And then you can just lower the amount of red on the selection.
Somebody else may have a better suggestion.
Thanks, I think that’s close, but it seems to decrease all levels- mid & low level values seem to also be decreased. Is it basically shrinking the histogram to the left?
PC
I also have to make the disclaimer that I’m no Photoshop expert, but the answer to this question is definitely Yes. If you don’t want to affect the shadows and midtones of a particular channel, you can use the Curves adjustment. For your question, you’d call up Image > Adjustments > Curves, pick the Red channel, and place control points (3 or so will do) along approximately the left 3/4 portion of the curve, making sure that the input and output values are the same, then bring down the upper-right point down to whatever value you wanted (these are rough instructions, just as a starting point).
You’ll notice, though, that this still shifts the color balance of the overall image towards cyan. Depending on what you’re ultimately after, I can immediately think of two other approaches that you can try (besides carefully selecting only the reds in your image and working with them). One is to decrease the saturation of the Red channel (Image > Adjustments > Hue/Saturation, select Reds from the drop-down box, then move the Saturation slider towards the left.
The other method uses the Channel Mixer (Image > Adjustments > Channel Mixer). Select Red as the Output Channel, then for the Source Channels, move the red slider towards the left and the Green and Blue sliders by equal amounts towards the right so that all numbers add up to 100%.
Right. That’s why I’m thinking to decrease only the brightest red.
This is kind of what one of the redeye reduction tutorials online said, but I still don’t understand. Why select pixels with blue & green less than X also?
A problem with the Magic Wand with redeye is the red that comes through the iris, but that doesn’t get selected (so you have a black pupil with a redish rim in the iris). I’m still having trouble figuring out the Select Color Range function.
PC
Because white, for example, is made up of 255 white, 255 blue, and 255 green. If you simply turn down the red to 200, you’ll be left with 200 white, 255 blue, and 255 green (cyan, in other words). So you only want pixels with a high amount of red and very low amounts of the other two colors. (Anything that LOOKS red to the human eye will be like this… otherwise what you have is orange, white, purple, etc.)
The Select Color Range function is simply a Magic Wand that works across the entire image, including discontiguous areas. You select the color that you want to affect (like the very bright red of a redeye) and it’ll select that same shade of bright red anywhere it shows up in the image.
IMHO, if all you want to do is get rid of redeyes, this method might actually be overkill 
You have to do too much work in each image. It’d be easier to just use a tool like Picasa, which lets you circle the redeyes and automatically fix them.
Sorry. That second set of colors should read 200 red (not white), 255 blue, and 255 green.
Yeah, Magic Wand has its limitations.
If your immediate concern is to remove redeye, this is what I do (like you said, there are a gazillion ways to accomplish the same task, but this makes sense to me, and maybe it will to you, too):[ul][li]Use the elliptical marquee to select the iris(es).[/li][li]Feather the selection. The amount depends on the size of the image, but you don’t need much (and it doesn’t have to be exact).[/li][li]Go to Image > Adjustments > Hue/Saturation.[/li][li]Select the Reds from the drop-down box.[/li][li]Move the Saturation slider to the left. Crank it all the way down if you want; this isn’t exactly a delicate operation.[/li][li]The iris should now be gray-ish. If it’s unnaturally bright, move the Lightness slider to the left until things look right.[/li]Click OK. Deselect the iris(es). You’re done.[/ul]
Zoom. Clone Stamp. Small Brush.
Yes, sorry, i should have recommended curves, not levels.
But if removing red eye is your main goal, the absolute best technique i’ve found is the one described in this Luminous Landscape article.
Sure, it takes a few steps, and at first it seems a little complicated, but once you have mastered the process you can get rid of red eye perfectly in about 30 seconds. And, because the technique uses layers, layer masks, and brushes, the only pixels that are visibly affected are the ones you choose.
Thanks. The replys were all helpful. I guess what I need is a tutorial on the principles of Photoshop. I was using one of 2 methods for red eye from online tutorials, but was hoping for (at least in principle) something where I didn’t have to select the red eyes.
I think I finally understand why selecting all pixels with high red values won’t work. I think the methods mentioned work pretty well, most of the time.
One final question: Is there a way to select pixels with with Red values >200 and with blue and green values <100? Or could you select pixels with Red values at least 50 more than blue and green?
Would that select those pixels that look red?
I don’t know if there is a way to select the pixels like that—as i said, i’m no expert—but even if you could, i’m not sure it would work. What happens if you’re trying to use that technique to remove the red-eye from a person who is also wearing a bright red dress?
What picker said, almost:
Zoom in, use your little lasso tool to circle the red pupils as a selection (or the magic wand selection tool). Feather this selection by a pixel or 3. With the eyedropper tool, click another area nearby that looks to be the CORRECT color for the pupils (instead of zombie red).
With the paint bucket tool, click the selected eyeballs and they turn to the newly selected foreground (corrected) color. Move on to the next photo. Total time elapsed: 10 seconds. Other areas affected, colorwise: Zero. I do it all day long.
The problem with that technique, i find, is that it tends to make the pupil a single color, but if you look at the pupils on a proper picture they usually contain multiple shades.
That’s why i like the technique i linked to above, because it gets the red out while maintaining the same range of tones as the original, and thus the result looks more realistic. It takes a little more time (about 30-60 seconds per picture), but i think the results are better. YMMV.
I personally follow Earthling’s method for situations like this. It seems to work fine. It depends on how accurate you want it, but really eyes tend to be small enough in frame so a fairly rough and ready method like he describes is suitable enough.