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Sharpening to the max!

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  #1  
Old 07-24-2005, 10:56 AM
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PatrickB PatrickB is offline
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Sharpening to the max!

Hey folks,

I was once again thinking over the techniques to enhance some photoshop things and one thing that always disappointed me was the sharpening.

Let's have a look on how sharpening works:

Sharpening is basically tricking the eye. A blurred gradient to another color is sharpened by filling the adjacent areas with the inverted color. Disadvantage: Halos. But why must there be Halos?

Photoshop calculates the inverted color by simply using the invert color (what a statement . It does not use the color on the other side of the gradient which would produce no halos at all. An example:

We have a gradient from yellow to green. Sharpening this gradient means PS adds magenta next to the green area and blue next to the yellow area hence it reduces in heavy halos. If it used the adjacent area as a fill color, there wouldn't be any shadows, but how can that be done?

An interesting question isn't it?

Wonder if any of you know a solution

Patrick
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Old 07-24-2005, 11:05 AM
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I've been pretty happy using FocalBlade to sharpen. It doesn't seem to introduce the color aberrations in the area of the edge, and it deals with halos very well.
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Old 07-24-2005, 11:30 AM
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Quote:
We have a gradient from yellow to green. Sharpening this gradient means PS adds magenta next to the green area and blue next to the yellow area hence it reduces in heavy halos. If it used the adjacent area as a fill color, there wouldn't be any shadows, but how can that be done?
yes, but then it wouldnt be 'sharpening', it would be blending or smoothing by gradient. sharpening can be done two different ways that i know of. i'm not sure which photoshop or the other programs use, but you can sharpen by contrast, or you can sharpen by brightness. i think psp uses by brightness.

if you look at a color wheel, the method you are describing in the part i quoted, is based on complementary colors. i would assume this is done for the sake of contrast. the complementary color of green is magenta and the complementary color of blue is yellow. thus, you get a nice contrast.

Craig
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Old 07-24-2005, 11:50 AM
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Craig, that is exactly what I am talking about!

PS uses the complementary color to add contrast, hence sharpen. If it used the adjacent color instead, there wouldn't be any halos, right? So the question:

How do you achieve a sharpening with the adjacent color instead of the complementary one?
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Old 07-24-2005, 01:09 PM
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patrick,

when you say 'adjacent' do you mean adjacent in the color wheel or adjacent in the image? i'm guessing you mean adjacent in the color wheel. so, if you had a green, you'd either turn it cyan or yellow. well, green next to cyan or yellow isnt going to sharpen so much as it is going to blend. obviously it's not a complete blend, but that's just talking about the pure colors.

quite honestly, i dont know what you could use to do what you want. like i said before, sharpening is generally done with either contrast in color or contrast in brightness. but, it would make sense to have degrees of this or even combinations of this, or to have a tool where you could set the sharpening parameters. i just dont know of such a filter/plugin or tool that would allow this.

sounds like a great tool though. maybe we can commission one to be written.

Craig
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Old 07-24-2005, 01:55 PM
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I would suggest you get onto thelightsright.com. You can download what is arguably the best professional sharpening tool kit available. It's free and comes with a superb how to tutorial. Definetly worth your while to check it out. I use it with outstanding results.

Dave
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Old 07-24-2005, 04:37 PM
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Dave,

I'll give this one a look, thanks!

Craig,

I did not mean adjacent in the color wheel but in the area to be sharpened! Let me give you an example about what I meant: Suppose you have a portrait with black background and the image is a little blurry so you decide to sharpen it. PS would sharpen this by adding complementary color to the other side of the gradient (what basically every edge is) and this is what produces halos:

The complementary color of the black background is white, so it will add white to the skin. The complementary color of skin is something blue-cyan and this is what produces a blue-cyan halo in the black background. Halos.

But what if PS would not use the complementary color to add it to the other side of the gradient, but increase the saturation instead on both sides. An edge is as we said just a gradient, so one color fades into another one. If you increase the saturation or opacity of both colors, this would narrow the gradient until you have an extremely sharp picture. Thus the gradient should be shrinked to a thin line, right?

Patrick
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Old 07-24-2005, 06:29 PM
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ah, ok. that's another matter then. that gradient is there for a reason. and the reason has somewhat to do with dithering/anti-aliasing. maybe not completely, but somewhat. if you raise the saturation on both sides, you're lessening the grays, whites, and blacks in the hue. that's what saturation is, a lessening of the grays, whites and blacks. you probably would get an increase in the definition of the edge, but not necessarily in all cases. you would also get a lessening in the anti-aliasing/dithering, i would think. not sure if all that would be good, bad or what. i would guess that adobe did what they did based on some sort of average result testing. not sure the saturation increase would give you as good an average over many cases.

but that's about as far as i can think with it at this point. it would be somewhat interesting to do a test on this. and i certainly wouldnt mind if there were more options in setting the parameters for things like sharpening.

Craig
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Old 07-24-2005, 06:59 PM
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Patrick

This post has lost me a little but not altogether.

Isn’t this the reason a lot of people change to LAB to do the sharpening

There is also an argument for sharpening the image a little and then repeating it many times

One last thing that I found
If you sharpen on a layer and then set the mode to "Darken"
Then only the pixels that have been darkened by Unsharp Mask Will be Added.
This is one way of eliminating the artificial "halo" that sharpening produces since the "lighter than" pixels weren't used.

Ken
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  #10  
Old 07-24-2005, 07:21 PM
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True, both posters

What I thought of was somethink like: You have color a on one side and color b on the other. Why not find the "edge point" where both of them come together (something similar to find edges but only producing a one pixel wide) and draw a line with two colors there and set the color on both sides to the same as the area "near the edge is".

I illustrated it a little in the attached image. Sharpening in LAB would also lighten the areas and hence shift colors
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File Type: jpg demo_rp.jpg (3.5 KB, 37 views)
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