# Tone-mapping - what does it mean, and how is it done?



## Iron Flatline (Sep 6, 2007)

I've seen this phrase mentioned plenty of times, and when I search these forums it comes up in context to HDR work.

I've also seen this come up as a discription of images that I have found to be quite attractive. 

But how do I tone-map? What does it mean? I have Photoshop CS2 and several cameras that can AEB, so I certainly have the tools available.

Soooo.... a primer, please...


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## Garbz (Sep 6, 2007)

While it is used in HDR the process itself is not HDR dependant. It basically makes a pixel's luminance value dependant on the surrounding ones. It is used to compress the massive dynamic range found in a 32bit HDR file back down into a standard 8bit image. Tone mapping is also responsible for the glow seen around some objects in HDR images where the brightness changes suddenly.


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## Iron Flatline (Sep 6, 2007)

Ok, I get that. 

How do I do it? Can you describe to me (roughly) the steps or process I would put an image through in order to tone-map it? Could you point me toward a tutorial?


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## Garbz (Sep 7, 2007)

Ahhh no sorry I can't. So far I have only ever done 2 HDRs with tonemapping, one in photoshop which didn't turn out too well, the other in Photomatrix which I fluked my way through the settings.

In photoshop you go to file -> automate -> merge to HDR to make a 32bit HDR image. 

To do tonemapping regardless if you have a HDR image or not, convert the image first to 32bit if it isn't already, and if it is then simply convert it to 8bit. This will bring up a dialogue where "Localised Adaptation" is photoshop's version of tonemapping.


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