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Improving colors/brightness in biology image.

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  #1  
Old 04-08-2011, 10:19 AM
hochl hochl is offline
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Improving colors/brightness in biology image.

Dear all,

I need some advice on improving an image using GIMP 2.6. I've had no luck enhancing the brightness and colors. I'll show you what I did to improve it, but until now the results haven't been completely satisfying.

I have a picture of a cell sample. If you look more closely, you will notice that the top left corner is darker than the bottom right area. In fact, the area that lies about 20% inside the picture is the lightest, with all corners being darker. I want that all areas have the same brightness and coloring.

Currently I'm doing the following steps:

1) Duplicating the image layer. Switching to the top layer.
2) Desaturation using the luminosity setting.
3) Gaussian Blur of 200, which creates a very smooth black and white layer.
4) Invert, so that the darker areas get lighter.
5) Searching the color of the darkest spot using the color selector and a area of 20 pixels for averaging of the color.
6) Using the Levels dialog to map the darkest color to 128, and the lightest color to white. Since the image only has a range of 20 values, the result has many visible color steps.
7) Using Gaussian Blur with 50 to smooth the colors.
8) Setting layer mode to overlay.

The result looks promising, unfortunately the colors on the left side appear yellowish, which is noticeable.

So ... my questions are:

Does anyone have a better idea as to how I can make the image appear even?
How can I fix the color problem with my current solution?

I'd be happy to hear your suggestions!

Cheers,
H.
Attached Images
File Type: jpg original.jpg (99.5 KB, 89 views)
File Type: jpg result.jpg (98.2 KB, 80 views)
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  #2  
Old 04-08-2011, 05:27 PM
Tony W's Avatar
Tony W Tony W is offline
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Re: Improving colors/brightness in biology image.

I found the picture to be intriguing hence me having a try. I do not know Gimp well therefore the following is based on using Photoshop CS5. Hopefully you will find the Gimp equivalent if these images of any help at all.

Biggest problem is that I am looking at something very foreign from the everyday therefore I suspect I may have missed what you are looking for but...

1. First image left original right my enhancement!
To try and even out the image it may be possible to use D&B. I added a blank layer filled 50% grey set to Overlay and painted with a brush set to about 3-5% to darken in an attempt to even out.

2. Second image left original right my enhancement!
Tried to enhance colour seperation a little by converting to Lab and applying strong curves set to Overlay - this still needs some D&B to even out.

Hope this might be of some help
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File Type: jpg cell.jpg (95.4 KB, 33 views)
File Type: jpg cell2.jpg (95.6 KB, 31 views)
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  #3  
Old 04-08-2011, 06:42 PM
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mistermonday mistermonday is offline
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Re: Improving colors/brightness in biology image.

H, I am not sure if this is what you are looking for but here is an example attached. I do not use Gimp but I would expect it has some type of adjustment curve tool or layer. I just applied a curve to brighten the areas that appeared darker. I added a blank layer set to Color Blend mode to adjust the color shift caused by the curve.
It is not clear to me how much of the texture you want to flatten if any in this image.
You could also do a Dodge & Burn but that would take a lot longer.
Regards, Murray
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File Type: jpg Hochl MM.jpg (159.6 KB, 33 views)
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  #4  
Old 04-10-2011, 07:36 AM
hochl hochl is offline
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Re: Improving colors/brightness in biology image.

Ok, first thanks for your efforts, both results look promising!

Gimp has most of the tools that Photoshop has, of course Photoshop can do a lot more, but the basic stuff is there. In the past I've used PS 6 quite a bit, but in the end, since I'm mostly running Linux, Gimp has won and I found similar workflows in Gimp that I had previously used in PS.

The main problem is that I would like an automatic dodge and burn on the light/dark parts of the cell image so everything has the same brightness, without these yellowish areas. I still do not fully understand why the dark parts, that get lighter by the overlay method, suddenly appear with a yellow tint. Can anyone enlighten me as to why this happens?

The second problem is that I have hundreds of images to adjust, so I somehow have to automate this process. My goal is to adopt a workflow in Gimp, and after I have determined the necessary steps, I would implement it using Python and PIL. I've done this for other image processing earlier -- it's of great help, you just have to understand how to reach the desired effect first.

For some selected images, I could very well use a manual method, so all kinds of tools/workflows to reach my goal are of interest -- thus my very generic question :-) I might even use Photoshop, if everything else fails.

The workflow I have described is my main method to lighten and darken real photographs, by using a blurred, inverted grayscale copy of the lower layer, in overlay mode. This usually gives quite good results, but with the cell photograph, the now-lighter areas are suddenly yellow :-/

EDIT: I've included another image where the color effect is easier to see. The bottom right is much brigther than the top left corner.
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File Type: jpg original.jpg (95.3 KB, 40 views)

Last edited by hochl; 04-10-2011 at 08:10 AM.
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  #5  
Old 04-10-2011, 10:02 AM
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mistermonday mistermonday is offline
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Re: Improving colors/brightness in biology image.

You definitely have a dilemma. If you switch your eyedropper to view the pixel values in LAB and look at the L numbers you will see that the Luminosity values are all over the map. They go from 39 (out of 100 max) in the top left corner to 57 in the lower left to 66 in the top right to 88 in the lower right to all over the map in the rest of the image. There light to dark gradients are plural and uneven in the image. Moreover all of the texture you are trying to retain is also all over the place. Curves are not going to help you, nor are blend modes. No automation will be perfect unless you wrote a custom filter. So one possible compromise for now might be to use an HDR application or plugin - like Photomatix. The Detail Enhancer tonemapping module will smooth out the image by reducing the luminosity of the highlights while increasing the luminosity of the shadows and midtones. You can create a preset and have it applied to all the images and run it in batch mode. You can have Photomatix open the image in Photoshop where you can have an action make some fine tuning adjustments. Heree is a sample attached below. There are still areas that might need to be manually tweaked around the left edge where the original was particularly dark.
Regards, Murray
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File Type: jpg Hochl2 MM.jpg (186.4 KB, 21 views)
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  #6  
Old 04-10-2011, 10:20 AM
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Tony W Tony W is offline
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Re: Improving colors/brightness in biology image.

Hundreds of images!! Well I definitely agree with Murray - you do have a dilema!

I am unable to think of any way to automate the task other than Murrays excellent suggestion (frankly I do not think that I would have thought of this method either ).
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Old 04-10-2011, 12:08 PM
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0lBaldy 0lBaldy is offline
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Re: Improving colors/brightness in biology image.

Have you tried "The Color Deconvolution plug-in" from 4N6site.com
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Old 04-10-2011, 12:17 PM
hochl hochl is offline
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Re: Improving colors/brightness in biology image.

Quote:
Originally Posted by 0lBaldy View Post
Uh, no -- I've never heared about this technique before, I will give it a try as soon as I am under Windows!
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  #9  
Old 04-12-2011, 09:54 AM
hochl hochl is offline
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Re: Improving colors/brightness in biology image.

Ok, it seems using commercial tools/Windows is not possible currently, due to cost constraints, so I'm bound to Gimp or other OSSoftware and Linux. I tried many things and the results always look disappointing, so I had to rescan all images with better lighting. They still have problems, but it's a little better now.

Is there some way to use PS plugins with an OSS tool and Linux, or a Gimp way to solve the problem?
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  #10  
Old 04-12-2011, 11:04 AM
mactis mactis is offline
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Re: Improving colors/brightness in biology image.

Just played with latest head build "rawtherapee" with it´s HSV slider and local contrast.

Plus Gimps plugin "wavelet decompose".
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