January 23, 2008 at 10:41 pm #1225
Quick intro: HDR(High Dynamic Range) is a technique where you take a scene that has more dynamic range (difference between the bright and dark areas) than the camera sensor/film can handle, and make a picture that has the dynamic range compressed to fit into something that can be displayed.
For example, the insides of the trailer there were very dark compared to the concrete building behind the trailer. I took several pictures varying the exposure, so that I captured the building in one picture and the insides of the trailer in the other picture.
Dim picture, I underexposed a little bit to give Qtpfsgui the most info I could:
Bright picture. The shutter is 9 stops longer here, but the inside of the trailer is only slightly overexposed:
When you are making a HDR, you want to vary the shutter speed between the pictures, and lock the aperture, focus, focal length, white balance, and the camera position. The range of shutter speeds depends on the scene, of course, like in that trailer I used 1/500 to 1 second. In general, you want to have one picture that covers the brightest stuff in the scene, and another that covers the dimmest, with enough in between that you don’t have any gaps.
Once you have your pictures, you need to map them down into a single image. Qtpfsgui is a fairly easy to use program for combining several images into a HDR, with a very extensive set of tools for tone-mapping the HDR down into a normal 8-bit jpeg. Once you have your images loaded into Qtpfsgui, the first thing you will see it is rendered as a simple HDR. From there you can start the tone-mapping process.
Try out all of the tonemapping functions on your image, as they sometimes give very different results, especially Fattal. Once you have a tonemapping function that you like, you can tweak the settings to improve it. You can then adjust the levels before you export your jpeg.
Several things I have learned that might help other people:
It is sometimes useful to adjust the exposure of the HDR before doing the tone-mapping. You can look at the histogram above the HDR to see if that is necessary. This is very important in images that have a HUGE dynamic range, like here in a picture of a grate in front of a mine shaft.
Some of the tone-mapping tools change the results depending on the size of the output, especially Fattal, so you can’t preview by doing a small version and then change the image size and get the same results.
There is a flickr group just for Qtpfsgui images, and some discussion specifically for creating HDR images in Qtpfsgui.
This picture was taken at 10:40PM, and the moon was very bright if I just adjusted the levels of the 30-second exposure, so I needed HDR to make the moon look right.
I hope this quick little guide is helpful to people.January 24, 2008 at 12:51 am #15003
Very cool, thanks!
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