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Photo Compositing Collage, montage, masking, selections, combining, etc.

Complex hair selection

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  #41  
Old 01-25-2006, 04:13 PM
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bart_hickman bart_hickman is offline
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That BGE is one of those little gems that doesn't get mentioned as much as it should.

Another object extraction method that I use when the background is extremely chaotic and variable, but the foreground object has reasonably sharp edges, is using the vector curve tool to draw a path around the object. You can carefully fine-tune the path, adding nodes or deleting nodes as needed to get a perfect fit. Then convert the path into a selection. This method is called for only in pretty small minority circumstances--the BGE deals with about ~80% of situations. Masking handles most of the rest.

I was going to mention that I often find it beneficial to run the noise removal tool on an image prior to erasing or masking--this smoothes out noise and/or jpeg artifacts that can cause splotchiness in edges.

Bart
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  #42  
Old 01-25-2006, 04:23 PM
Ken45140 Ken45140 is offline
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Bart:

Chaos like in this image from another thread? Even the triple screen on the second version, which shows the hair a little more clearly, is still a bear to try and extract. I have tried all sorts of approaches (in PSPx and PS7) and have nothing to show for my 60+ cumulativer minutes working on it. I actually don't think it can be done because of the common color pixels all mixed in with the hair and the wall or vice versa. Esp in the lower right and lower left areas. I notice that no one here has tossed up an "extraction" solution for this one.

Ken
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File Type: jpg Hair07.jpg (98.6 KB, 55 views)
File Type: jpg Hair07b.jpg (37.1 KB, 62 views)
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  #43  
Old 01-25-2006, 10:34 PM
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bart_hickman bart_hickman is offline
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Really hard

That's a pretty pathological situation. I used my previous method--it's at it's limits. I had to apply a curve to the girl depending on the background to make her exposure appear to match. I also did some smudging on Mask 1 and 2 to smooth them out a bit as the original was noisy and artifacty.

Bart
Attached Images
File Type: jpg girl_clouds.jpg (38.1 KB, 62 views)
File Type: jpg girl_leaves.jpg (59.2 KB, 54 views)
File Type: jpg girl_rainbow.jpg (34.5 KB, 57 views)
File Type: jpg girl_stars.jpg (44.5 KB, 58 views)
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  #44  
Old 01-26-2006, 07:27 AM
Ken45140 Ken45140 is offline
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Bart: You are the master! Do you mind showing me the settings on your Channel Mixer dialog boxes or just write them in text. I'm motivated to give it one more go since I see there is a light at the end of the tunnel. OTOH, maybe I need to practice on another 100 or so before coming back to this one.

Ken
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  #45  
Old 01-26-2006, 11:20 AM
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creeduk creeduk is offline
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Talking of Russel Brown, check out his podcasts, he has a new one, extreme masking using multiple methods to really get the mask down!
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  #46  
Old 01-28-2006, 02:03 AM
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bart_hickman bart_hickman is offline
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Part 1

Quote:
Originally Posted by Ken45140
Bart: You are the master! Do you mind showing me the settings on your Channel Mixer dialog boxes or just write them in text.
Ken
You're too generous!

This extraction has to be done in sections because the background/foreground relationship isn't uniform. The image is also noisy so it's a good idea to do some NR prior to starting. I did three major sections (left, top, right), plus a little bit of cleanup between sections.

Starting with the top first, do the following steps:

-A quadruple screening of the image to brighten up the hair relative to the background wall--you basically did this already.

-Make a small selection (~5x5 pixels) on her forehead--doesn't matter where. (This initial selection is due to a peculiarity in the select color range tool--it needs a seed selection to begin. I've already complained to Corel about it.)

-Make sure the screened image is the active layer and zoom in to about 200-300%. Selections->modify->select color range. Now move your eyedropper (1x1 pixel sampling) carefully over the center of a bright strand of hair and sample it. This becomes the comparison color and the select-color-range tool will select colors similar to this sample. Adjust the tolerance and softness to reasonably capture the hair strands you want while only getting a small amount of background. The 1st attachment shows how the preview window could look after tweaking. Don't copy my numbers exactly--they'll vary a bit depending on exactly where you sampled. Since you can see the selection in real time, simply adjust it to look good--I err towards capturing some background in order to get more foreground. This is because the defringing steps will remove the excess background anyway. Click okay. You should now see the "walking-ants" selection marquee.

-Right mouse click over the active layer and choose "new adjustment layer->curves". This pops up a curve tool. Make a curve roughly like I show in the 2nd attachment. This boosts the brightness on our selection from the previous step as you can see in the before/after panes. Click okay. You'll notice in the layer palette that the curve adjust layer you created has the alpha channel from your selection applied to it (see 3rd attachment.) The brightness boost applies more strongly to the brighter parts of the alpha channel as you see in the 2nd attachment.

-Invert the selection.

-Create another curve adjustment layer--this one will have the inverse alpha channel of the first one. Make a curve like the one in the 4th attachment. This darkens the background. Play with the curve a bit to see what it's doing--sometimes a linear curve isn't the best choice--I just used it here for simplicity. For a linear curve like this, you could have used the levels adjustment layer. (I'm an engineer by profession, so the curve is much more intuitive to me .) Click okay.

What we have done is create a mask for roughly the top third of her hair. The sides need a separate procedure including some hand-brushing the create some hair on the left side because there's no usable contrast. Notice I didn't use the channel mixer--that's because the foreground/background was already well-distinguished by luminance. This will not be the case for the sides. I'll do the sides in coming posts as well as how to combine the three sections.

Bart
Attached Images
File Type: jpg select_color_range.jpg (44.4 KB, 57 views)
File Type: jpg boost_curve.jpg (35.8 KB, 44 views)
File Type: jpg palette_w_curve_adj.jpg (13.6 KB, 38 views)
File Type: jpg unboost_curve.jpg (54.3 KB, 41 views)

Last edited by bart_hickman; 01-28-2006 at 02:40 AM.
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  #47  
Old 01-28-2006, 02:39 AM
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Part 2

Now for the right side. It has less distinction in luminance, so we need to mix channels to help this. In this region, the background is strong in R & G and weak in B. The foreground (hair strands) is slightly strong in R, very strong in G, and medium in B. So compare the relative strengths and weaknesses between the two.

Rf < Rb
Gf > Gb
Bf > Bb

On top of that, the foreground luminance is greater than the background luminance.

To translate all of this into only luminance, we accentuate these differences. So I pop open a channel mixer. Red will get turned down (darkens the background more than foreground), Green and blue get turned up (brightens the foreground more than background.) I could write a formula for exactly what the sliders should be, but it's easier to just start with the general directions and go by sight after that. The 1st (and only) attachment shows how the channel mixer looks and how the hair strands have been somewhat accentuated. Let's leave this for now and do the left side of the head (next post).

Bart
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File Type: jpg channel_mixer_pt1.jpg (45.6 KB, 49 views)
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  #48  
Old 01-28-2006, 03:26 AM
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bart_hickman bart_hickman is offline
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Part 3

(Addendum: the attachments didn't come out in the correct order for some reason.)

Now for the left side. What a mess. There's no difference in luminance here at all and a tiny difference in hue and saturation. Looking at the RGB as we did for the right side, the hair strands are strong in red and weak in blue compared to the background. So pop up a channel mixer and crank red up and blue down to make the most of this distinction. I adjusted green to get things centered up. The 1st attachment shows how the channel mixer preview looks. I managed to bring out some contrast, so now do a curve layer (shown in the 2nd attachment.) I'm done--it's clear at this point that the noise is larger than the hair strands so I'm going to have to finish this one up with a hair brush. We'll do that along with the rest of the clean up after everything is combined.

To combine, we simply pick the best from each of the three sections and black out the alpha channel of the adjustment layers that weren't the best. The 3rd attachment shows my layer palette so far. In the group called "Mask 1, top, left, right" are all of my adjustment layers thus far. There are a couple of extras I didn't talk about--but you've seen at least one example of every trick thus far and I'm trying to keep this thing minimized.

You also see in the 3rd attachment a layer group called "Mask 1, combine". This has the three merged results from the three previous sections. I'll simply flip around through the three sections and keep the best parts from each one by selectively erasing. In some cases I even end up with some mixing between sections.

After some soft erasing from each of the sections, "Mask 1, combine", looks like the 4th attachment. The top and right look good--I'll just need some burning to fix those. The right side merely provides guidance on how to use a brush to re-create the hair strands over there. We're not done, but I think you can see the total mask emerging. Now I'll merge this and start the final phase of the Mask 1...next post (I'll try to finish up tomorrow.)

Incidentally, this all seems cumbersome, but it's really not--if I weren't explaining it, I wouldn't be saving all of these steps and I'd only be about 15 minutes into it at this point.

Bart
Attached Images
File Type: jpg channel_mixer_part3.jpg (37.4 KB, 30 views)
File Type: jpg curve_part3.jpg (42.0 KB, 30 views)
File Type: jpg mask 1 combine.jpg (22.4 KB, 40 views)
File Type: jpg layers_after_part3.jpg (23.5 KB, 30 views)

Last edited by bart_hickman; 01-28-2006 at 03:31 AM.
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  #49  
Old 01-28-2006, 01:10 PM
Ken45140 Ken45140 is offline
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Bart: Amazing!! I am just done with part 1 and am needing to take a break. This is teaching me so much.

You don't spell it out (because you are so used to it) but creating layer groups ahead of time seems essential to turning the group layer into a mask. This is true isn't it? The create mask choice is greyed out when selecting the curves adj layer. Second, I found I had to do some painting on the mask itself as I never got a "clean" one even after color choicing and curves adj. Practice should make this better. But I finally see the approach.

I'll report back after parts 2 and 3 and after more iterations on the technique.

Many thanks.

Ken
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  #50  
Old 01-28-2006, 01:57 PM
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bart_hickman bart_hickman is offline
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I do have the image and the subsequent adjustment layers all together in a group--yes. PSP creates a group automatically when you create a mask because that's nearly always what you want to do anyway.

It's not essential that you create the group ahead of time--you could do the work first and then dump everything into a group later as well. Even when I don't *need* a group, I use them to organize things. When you get to part 3, I posted a picture of the layer palette to that point to show the groupings.

Bart
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