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cleaning up purple, blue and white spots

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Old 09-08-2011, 12:24 PM
John Wheeler's Avatar
John Wheeler John Wheeler is offline
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Re: cleaning up purple, blue and white spots

Hi N. Fotis

Thought I would through in another angle to get rid of those blue splotches. I am not sure that GIMP has all the functionality as I use in my approach yet I bet it could be done. I developed a technique that helps "phase" out the luminosity of undesired colors. My first use of this was actually to get rid of certain sensor based Moire patterns yet works quite well in other situations. Here is the link to that blog:

Once the luminosity of the bad color blotches are taken care of then there are many ways to blend back in the color you want. Tony mentioned a very good way which is just pointing in the color you want with either the brush set to Color Blend or the layer set to Color Blend.

I took a different approach on the images below which was to create a mask of the blue blotches and then slightly desaturate those areas. So this was done without brushing colors in where needed, just layers and layer masks. The mask was created by subtracting green channel from the blue channel and then doing a levels adjustment. This is just one of many approaches to get rid of the blue blotches once the luminosity is matched.

In the images below I did not bother with the sky since that was a different and easier issue to fix.

Your original image:

Luminosity of image after phasing out the color blotches per my blog:

Here was the desaturate Mask:

Here is the final image (sky masked back t original image):

I bet there is a way to do the same things on GIMP yet I do not have a copy on my machine to try it out. Hope this helps
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Old 09-08-2011, 03:10 PM
nfotis nfotis is offline
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Re: cleaning up purple, blue and white spots

Hello again,

I made some attempts, but it seems that it is not that simple to replicate these tricks in GIMP. And I am not very conversant in masks etc.

Because my brain is half-fried, I will make another attempt in the weekend to replicate these tricks (at worst, I have one version of the photo ready).

Now, I am struggling with a very nasty case, with tiny black spidery marks (I suspect these are from fungus again), I will review the forum for any ideas after I do some experimentation.

Nick the Greek
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Old 09-08-2011, 04:44 PM
nfotis nfotis is offline
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Re: cleaning up purple, blue and white spots

Just for the record,

- GIMP has no adjustment layer (you can 'create a new from visible' layer, though, if that means anything)

- GIMP is inside an RGB machine, so working in other color systems is a problem. You can decompose to layers in various systems, e.g. in LAB you get the L, A, B layers

- You can do various combinations of layers in GIMP using modes as 'multiply', 'divide', etc.:

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Old 09-09-2011, 05:15 AM
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Tony W Tony W is online now
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Re: cleaning up purple, blue and white spots

Nick I cannot offer much help on Gimp it is so long since I used it - now that you have mentioned it I remembered that it does not have adjustment layers (at least the version I tried).

I guess that decompose to layers and the opposite recompose should get you in and out of LAB - exactly how I am unsure

Gimp does have 21 layer modes including color so it should be possible to dup the image and set dup to color then paint over, if it is not possible to do with a blank layer
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