June 29th, 2008


Playing with HDR ...

I have a new toy. It goes by a name only a geek could love - "qtpfsgui" - a name that tells you in great detail what it is, and almost nothing about what it does. Briefly, it lets me do two things - first, combine two (or more) differing exposures of the same scene to form a High Dynamic Range (HDR) image, and second, performing "tone-mapping" on that image to allow it to be viewed as a normal non-HDR image again (e.g. in JPEG format).

In this case, the first image below was as it came from my camera - it looks like the camera has exposed it well for the sky (the clouds are nicely detailed), but left the rest somewhat under-exposed. The second image (to its right, assuming your browser window is wide enough (and hopefully not blowing up anyone's friends page if not - please let me know!)) was simply created using The GIMP (*sigh* another geeky name ...) by brightening the first image until a fair amount of the shadow detail on the walls was visible. I loaded those images into qtpfsgui, then used the tone-mapping function there to create a best-of-both-worlds version that has most of the detail of both, in the third image.[1]

I did the same for a photo of Dunrobin Castle (below the cut) - again, I had the same sort of slightly under-exposed starting image, created a brighter copy, then ran the HDR/tone-mapping to create the third image of the second set. qtpfsgui has a number of different tone-mapping transformations to use, and suggests that you try all of them until you get close to the desired result. The final photo of Dunrobin shows that not all of the tone-mapping algorithms produce ... "normal" results, although it's still a strangely interesting image.

(as always, all images here are linked to larger versions)

Base image, Broch of Gurness Brighter image, Broch of Gurness

HDR/tone-mapped image, Broch of Gurness

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