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Tone Mapping


Tone mapping is the process of mapping one color space to another.

There are many reasons to tonemap an image, and they can be summed up in two groups:

  • To reproduce the same tonal response on devices with different response curves.
  • To manipulate an image and highlight specific structures of interest (e.g. in medical imaging), or make it aesthetically pleasant and convey particular emotions in the viewer.

Manipulation is open-ended. The application drives the functionality. There is room for variety and creativity. Judgment is mostly subjective, particularly when the purpose is an artistic one.

I respectfully disagree with the opinion that tone mapping operators should have the function of tone reproduction only, even if it is expressed by Erik Reinhard, an expert on tone mapping and inventor of powerful tone mapping operators. Erik states that “if he wanted the image to have a specific ‘look’ or ‘feel’, he is perfectly capable of running the image through a set of Photoshop filters”. Sure, why not. But why not running the image through tone mapping operators as well?

Reproduction is a holy grail. Sometimes justified, e.g. for a reporter who wants to convey facts not opinions.

Pursuing high fidelity reproduction only crowds researchers in a mutually exclusive space where there can be only one winner, the one that achieves the most “natural look”. But what is this reference “natural look”? In the old days it was the debate of Fuji vs. Kodak color. In this early digital age our eyes have been trained to accept as “natural” the rudimentary output of sensors that in some areas still lag the silver-oxyde coated celluloid. With a lag of a few years we are afflicted by the same problems that afflict music.

I understand some people don’t like what they call the “artificial look” of images tone mapped with “parameters that are vastly outside its useful operating range”, and I respect that. It’s subjective. Not everybody likes my art, and it is perfectly acceptable so.

Erik Reinhard’s opinion reminds me of many inventors who have seen their inventions used for a different purpose than intended. Embrace the applications, don’t fight them! Why limit yourself?

Below is a sequence of tone mappings of the same image, most of them done with HDR/tone mapping software like Photomatix or qtpfsgui. My objective was to create an artwork, that is called The Future of the Oil Industry. Click on the image to see a full spherical version with the currently retained tone mapping. As an artist I reserve myself the right to revisit my art, like painters used to do in the old day.

Photography is painting with light. Like it or not, tone mapping operators are here to stay as part of the modern photographer toolbox. Thank you for giving them to us, the more the merrier!

2 Responses

  1. I commented on Erik Reinhard’s piece on my flickr page http://www.flickr.com/photos/sbprzd/2699695242/
    In particular I show that enfuse is quite comparable to the best tone mapping operator in Erik’s view…

  2. i quite like the result. makes me ‘wanna try out exposure bracketing soon!

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