HDR from a single image

As promised, here’s my next foray into the realm of HDR. I ran a single RAW image through the Photomatix Tone Map. I guess it isn’t technically an HDR, just the Tone Map. Still, I wanted to see the impact.

The following is from the FAQ section of the Photomatix web site:

You can still use Photomatix when you have shot only one exposure in RAW mode. The big advantage, of course, is that you just need one image, so there is no need to use a tripod or to remember to auto-bracket, and it will also work if the subject is moving

However, the range of “workable” exposures you can get from a RAW file is limited. If you are shooting a high contrast scene, you are unlikely to match the results you would have with taking the scene under different exposures that can cover the whole dynamic range.

There are three techniques for using Photomatix with one single exposure taken in RAW mode:

· Technique 1:Open your RAW file in Photomatix to convert it into a pseudo-HDR image, then tone map it.
· Technique 2:Convert your RAW file into a 16 bits/channel image in your favorite RAW converter, open it in Photomatix, and tone map it.
· Technique 3:Create two or three exposures in your RAW converter and combine them in Photomatix as it they were “real” bracketed shots

For good results with these techniques, it is important to ensure the lowest noise level at capture time. For that, set the lowest ISO possible (ISO 100 for instance) and expose for the shadows when taking the RAW image, i.e. overexpose your shot. Even though the histogram of your camera may indicate that highlights will be lost, you should still be able to recover them during RAW conversion (unless the scene is too high contrast, but then a single image will not be sufficient for good results with Photomatix).

Deriving “fake” exposures from a single RAW file (technique 3 above) is theoretically an improper way of creating a 32-bit HDR image. If you intend to use the HDR image file for 3D rendering, then you should not use this technique, as you will not get accurate linear pixel values required for image based lighting. However, if you are only interested in the tone mapped result, then creating “fake” exposures is a valuable technique, as long as you get improved results over technique 1 or 2.

I picked a shot I took a few weeks ago of a hillside of fox tails and other assorted weeds. I loved the texture and the subtle color shift.

I popped the white balance up in the Tone Map since the original exposure range was pretty narrow. This brightened it up a bit. And I popped up the saturation just a bit – because I liked it. I left the rest of the Photomatix settings at their default. After I processed it I pulled it into LightRoom and did the normal LightRoom adjustments – White Point/Black Point and I sharpened it quite a bit (0 to 50).

Then I compared it to my LightRoom adjusted original. The original was significantly brighter (my normal tendency is to over expose everything -comes from being a commercial/fashion photographer in the mid 80’s). So I pulled down the brightness just a tad to bring it closer to the Tone Mapped image.

This is a side-by-side comparison of the full image – the Tone Mapped image is on the right: 

 Again, the differences are subtle, but they are there (click to enlarge).

2009_0604_0008_FullCompare_lrg

The Tone Mapped image is just a tad richer in color and when you get real close and personal you see just a touch more detail in the highlights. Here’s a close up of the bottom right corner of the image to help see that (click to enlarge):

 2009_0604_0008_TightCompare_lrg

The contrast is a touch less and the image just feels a bit more open.

I’ve created larger images and I’ll link them as soon as I figure out how to do that, then you’ll be able to see it better.

Again, what I love about this is the extra level of subtle detail it brings out in the highlights and shadows and the slight increase in richness of the color. It isn’t sharper, its more detailed.

I’m still keeping the HDR/Tone Mapping adjustments to a minimum so I’m not getting the ‘wow’ effect that most of the HDR out there is associated with. We’ll play with that another day. For now, I’m enjoying the subtle touch. And I expect that is what I’ll come back to.

Next time I’ll try Technique #3 – create 2 or 3 different exposures from a single RAW file and run those through Photomatrix.

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