Retinex

I stumbled upon ‘Retinex’ filter which is available free in GIMP. Retinex is a theory, developed in 1971 by E. H. Land, and deals with human color perception under varying lighting conditions.  Regardless of the theory, I tried it to boot contrast and details in images. The out come is dramatic and I thought to share the experience.

1. The base image, of my younger brother:

DSC_1707

The image is not bad to begin with. But I want to increase contrast and details.

2. Duplicate the layer. In the copy layer (call it ret), run the Retinex filter with the default values. This gives the following image:

DSC_1707ret

The effect is dramatic and in this case too intense. Occasionally this is all an image may need. To mellow it down,

3. Change the blend mode of ‘ret’ layer to overlay and set the opacity to 50% to get

DSC_1707retol50

You can change the opacity level to control the effect. 50% usually will work for majority of the images.

That is it. The above may be taken as the final image. although many other techniques can be mixed.

My interest, however,  is to get a punchy black and white image.

4. Flatten the image, convert to black and white. I used channel mixer red=31, green=36 and blue=33 settings to get:

DSC_1707retol50bw

Again, I may stop here as it is the look I want in my conversions. However, I tried one more cycle.

5. Run retinex once in a new layer, overlay with 25% opacity this time as 50% was too much.

THE FINAL IMAGE

DSC_1707retol50bwretol25

Please note that I have not touched levels, curves, sharpening etc to show the usefulness of this very powerful filter.

I hope you enjoy. Please try it  if you fancy and let me know about the experience.

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Posted in Photography
12 comments on “Retinex
  1. This is interesting to look at various versions. I find the images using the filter to be unreal. Your younger brother’s hair does not look real. However, it is fun to play. Thanks for sharing the results of the filter.

  2. Son of Sharecroppers says:

    Very fine work! I admire your technical skill. The portrait is superb.

  3. jlmphotos says:

    Very Interesting series. The BW ones are my favorites – both of them actually.

  4. Son of Sharecroppers says:

    A comment: I’ve been working my way back through your blog, and I came to this post. I thought that I had “liked” a couple of previous photos, but I thought that perhaps I’d seen them in the reader and hadn’t clicked on them. But I knew that I had not only “liked” this photo but also commented on it. But when I returned, my “like” had disappeared! Very odd.

    • Dr_IQ says:

      This sometime has happened to me also. Others have also complained. Sometimes I see ‘like’ on a photo which I did not clicked. Some glitch in the wordpress software I guess.

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