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CS5: Color range selection issue

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  #1  
Old 08-05-2011, 08:16 AM
KarimNassar's Avatar
KarimNassar KarimNassar is offline
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CS5: Color range selection issue

Hello
I stumbled on this issue when using a color id pass from a 3d software.

Here's an example of a color id pass:

http://area.autodesk.com/th.gen/?z/h...iwa6:720x0.jpg

Just like a mask in photoshop, the model is separated into different parts but instead of black and white it is done using flat colors.

So all you have to do is color pick the area you want and you have that area isolated for retouching.
Sounds useful except that it gave me nasty fringes.

Now maybe I'm doing it wrong you tell me.

I tried it again with a picture I created directly in ps, using the pen tool and filling the selection with pure red:R:255 G:0 B:0 :

http://img801.imageshack.us/img801/7025/colorrange1.jpg

I then duplicated the layer and set it to difference mode and as expected it lines up perfectly:

http://img88.imageshack.us/img88/6800/colorrange2.jpg

I then selected the red using the select-color range command. I tried a couple fuzziness settings from 0 to 200 and filled the selection with red. And here comes the fringe:

http://img10.imageshack.us/img10/4170/colorrange3.jpg

What am I doing wrong?
How would you go to have clean color selection that allows retouching without fringes?

thanks!
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Old 08-05-2011, 05:44 PM
John Wheeler's Avatar
John Wheeler John Wheeler is offline
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Re: CS5: Color range selection issue

Hi KarimNassar
I may not understand exactly what you are trying to do yet lets start with your experiment.

When you create a filled vector or selection the edges are anti-aliased so you do not get just two zones of two unique colors. The edges slowly fade from one to the other. When you use the Color Range tool its algorithm is not exactly picking up all the different shades between the red and white. Not surprising. Duplicating any image and doing a difference blend will always yield black mathematically.

If your color id pass of the your first image is truly just 4 colors, then you can use the magic wand tool with the tolerance set to 0 and individually pick the colors to get the unique non overlapping selections.

If there is anti-aliasing in your first image and you want hard non-overlapping selections, then you need to effectively posterize the image into a smaller set of unique colors. There are various ways to do this including the posterize adjustment layer and other approaches utilize the Threshold adjustment tool.

I do not know know what exactly you are trying to retouch nor if these images are just an intermediate step to something else you want to do. Hope this helps and if not or if not just ask more questions and include more details on what you are trying to achieve as the "end" for your project and it may be easier for forum members to help. Good luck in either case.
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Old 08-08-2011, 04:59 AM
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KarimNassar KarimNassar is offline
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Re: CS5: Color range selection issue

Hi John thanks for taking the time to answer!

I do understand that due to anti aliasing we don't get exactly two colors but some shades on the edges to have the smooth outline.

And that is exactly the issue.

To answer your question, I want a clean selection of the blue part in this pic:

http://img824.imageshack.us/img824/9571/testqg.jpg

I tried what you said with the magic wand and it still has the same issue.
And posterization is not an option because the outline becomes jaggy as expected.

Here is what I invite you to try:

Save the pic I provided above.

Select the blue, create a level adjustment layer and bring the black output to 255.
If the blue is selected properly then it should disappear (turn to white on white background).

Except that I get a fringe like this:
http://img16.imageshack.us/img16/8324/fringeg.jpg

Now I could select the mask, go to filter: other: maximum, to expand the mask.
But that is not a solution because it goes too far out even with the minimal value.

The mask refinement window shift edge option does help a bit but it still leaves a small fringe.

So how does one select a pure color with smooth edges properly in ps?
thanks!
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Old 08-08-2011, 08:07 AM
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John Wheeler John Wheeler is offline
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Re: CS5: Color range selection issue

Hi KarimNasser
I think I can solve your problem yet want you to check one thing before we go further.

It turns out Photoshop display anomalies can cause exactly what you are seeing at below 100% magnification and especially at 50% and below.

Either stamp your image before viewing and/or view at 100% magnification or larger.

Here is the comparison.

Here is your image viewed at 25% magnification with the Layer stack you indicated and note the blue dotted outline (click on thumbnail):

25% mag no stamp.png

Now all I did was make a top layer that is a stamp of the image using CMD+OPT+SHIFT+E (CTRL+ALT+SHIFT+E for PC). Note that the blue fringe is gone:

25% mag with stamp.png

Now this may not be your issue at all yet wanted to get that out of the way. If it is not your issue, then also note that in the second image I did create an end result where there was no blue fringe. I can go over the process I used if you aren't just seeing a display anomaly.
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Old 08-08-2011, 10:44 AM
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KarimNassar KarimNassar is offline
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Re: CS5: Color range selection issue

Hello thanks for stopping by, it definitively is not a display anomaly, I tried the magnification and the flatten layers in a new layer but the fringe is still there.

Curious to know how you achieved the clean selection!
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Old 08-08-2011, 03:30 PM
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John Wheeler John Wheeler is offline
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Re: CS5: Color range selection issue

Hi KarimNassar
Glad to hear it was not a Photoshop display issue. Those have bitten me in the past.

All I actually did was use the magic wand tool. I zoomed into the image at this location:

Screen shot 2011-08-08 at 2.15.29 PM.png

I set the magic wand to contiguous and turned off anti-alias. I then took trial selections with the magic wand tool in the blue region increasing the tolerance setting until I got what I thought you would want. The final value I used was a tolerance of 200 to get the marching ants selection shown.

Then I just added a pure white layer on top and converted the selection to a Layer Mask. I stamped the image so when displaying I would not show any fringe in the image below. Here is the final result and the Layer Stack:

Screen shot 2011-08-08 at 2.17.56 PM.png

Not using anti-alias produces a sharpe edge mask so you can either leave anti-alias on or feather the mask if you want a smoother transistion.

Hope that helps.
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Old 08-09-2011, 05:28 AM
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KarimNassar KarimNassar is offline
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Re: CS5: Color range selection issue

I tried your steps but sadly the selection still is not quite right. Like you said the edges are sharp so produce bad results when using the mask on adjustments layer or stamping etc and feathering reduces the accuracy of the selection.
I will ask on 3d software forum, since they use those color id pass regularly they are most likely to have the solution.
I'll drop by if I find the answer!
thanks again
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