Question about this photo

I have seen this happen when converting a jpg to a gif with limited colors. Did you at any time lower the number of colors used in the jpg, like lowering the quality drastically for the forum? This will cause the smooth transition of colors or brightness to show a terraced effect like you see here.

Also, what software were you using? No two programs use the same algorithms to process image files. Some less popular programs are not as strong as the top name programs.

No, this happened already in Photomatix when I tonemapped the image, I tried to tone map it differently but with no results. Then I saved it as 16 bit TIFF and opened in Photoshop CS4 just to resize and post it here to ask you guys. Resized in Photoshop CS4 and saved as .jpg, 10 quality.

Which version of PM? Do you have the latest update?

Photomatix Pro 3.0. No, I haven't updated it, I didn't even know there was an update..

But do you really think it could be because of an update? Maybe I did something wrong with tonemapping?

In your case, yes, v3.1.1 was lightyears ahead of Version 3.0. It's a free update, you should go get it and try it.

Or, if you can, upload your RAW file where I can download it and I'll try it.

Thanks very much. I will try with that!

The artifact you are getting is called posterization. There are not enough data in that portion of the image to get smooth transitions in tone for the tonemapping you are applying. When you are tonemapping, you are trying to add contrast to an area that can't support it, so you get the banding, or posterizing, as you see above.

Attached, and in the following post, are examples of the phenomenon. I generated a white to black gradient in Photoshop, rendered in 8 bit gray (256 levels of gray). I then used the "Posterize" adjustment to re-render the original gradient in decreasing levels of gray (noted by the text labels in the figure). As you can see, after about 128 levels of gray, noticeable posterization or "banding" appears evident and our original smooth gradient becomes divided into discrete patches of tone. As can be appreciated, each block of tone appears to have a slight gradient within it - if you use the dropper tool to check the gray level, however, you will find that the gray level is essentially constant over the entire block of tone. This is a well-known psychovisual phenomenon that has to do with the local contrast between two adjacent tones creating the illusion of a change in tone (google "Mach banding" to learn more - here is an interactive app to experiment with Mach banding: http://www.nbb.cornell​.edu …/anson/MachBand​ingApplet/). (As an aside - unsharp masking takes advantage of our brain's trickery by creating local contrast at an edge to give the appearance of a sharper image).

In your image, the posterization is likely the result of the tonemapper having insufficient data with which to work. So, essentially, the sky data in that area of the image has run out within the context of the tonemapping curve you are applying (or PM is applying) and the tonemapper is trying its best to fill in the gaps.

Try again with multiple exposures shot with the camera (not made with a RAW converter, from a single RAW image) and your skies will appear more continuous in their tonemapped rendition. What you have discovered is that a single RAW image is not capable of capturing the full dynamic range of your scene - i.e., a single RAW image is not a "high dynamic range" image - no matter what you do with that single RAW image (i.e., with the "exposure" sliders in ACR) you are not creating any more real data than that contained in the original, single capture. That's why you usually have to shoot a sequence of exposures to capture all of the data in a truly high dynamic range scene.

Have fun!

Kirk

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Below is an example of what happens when you try to make a tone mapping adjustment (i.e., a curves adjustment) that is too steep (i.e., trying to create a lot of contrast) where the data can't support the curve. Shown is our original gradient (bottom of image) and the tone-mapped version with a super-steep curve applied (top of image). The image is rendered in 256 levels of gray, but the attempt to eek out a ton of contrast over a very small number of gray levels gives a banded result.

Try tonemapping your image in ACR and/or using curves in PS and you will likely have more control over fighting the banding issue.

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Thank You very much for detailed explanation. I've never heard about this phenomenon, though I supposed I was getting it because the original sky was pretty much blown out, therefore there were not enough data in that portion of the image to get smooth transitions in tone as you explained. Nice to learn something new!

I have got better results with an updated version of Photomatix but these transitions are still visible.

Cool.

Kirk

That's good to know too.

Thanks for all the help guys, I appreciate it!