High Dynamic Range (HDR) II

There is a lot of hype recently on photo websites about HDR (high dynamic range) processing.  Photographers show beautiful images, tell people they were HDR processed, and everyone naturally wants to make their own beautiful images.  Naturally!

I’ve also have had many questions recently on HDR and during my last 10-12 workshops HDR has been a requested learning topic.

Months ago I covered the basics of HDR and I’m going to do so again this week.  I’ll do it a bit differently, but just as simple and basic.

First, you want to really look at the scene and see if you want to use HDR.  Many are under the impression that HDR makes ordinary images better.  This would not be correct.  Only scenes that would benefit from HDR should be shot and processed as HDR.  Otherwise you end up with an image that was obviously processed and who wants that?

Scenes that benefit from HDR are scenes where the dynamic range of the scene exceeds the dynamic range of the camera being used to capture the scene.  If the entire dynamic range of the scene can be captured with one image, then by all means use one image.  If it’s the “look” you’re after, then you’ll need to learn advanced processing skills.

If the dynamic range of the scene exceeds that of the camera then it’s time to capture and process HDR images.  Let’s look at the following scene.

 

The middle image is correctly exposed by the histogram.  The -1 image is one stop underexposed and the +1 image is one stop overexposed.  Looking at the idle image I can immediately see that the rice fields are correctly exposed, but the clouds have lost a lot of detail and definition as has the sky.  Notice the increase detail/definition in the clouds/sky of the -1 image?  Notice the tree line to the right middle?  It’s dark in the 0 and -1 images, but well exposed in the +1 image.  Each image of the same scene, exposed to a different value, has elements I’d like to see in the final image.

The middle image is correctly exposed by the histogram.  The -1 image is one stop underexposed and the +1 image is one stop overexposed.  Looking at the idle image I can immediately see that the rice fields are correctly exposed, but the clouds have lost a lot of detail and definition as has the sky.  Notice the increase detail/definition in the clouds/sky of the -1 image?  Notice the tree line to the right middle?  It’s dark in the 0 and -1 images, but well exposed in the +1 image.  Each image of the same scene, exposed to a different value, has elements I’d like to see in the final image.

 

The final image is much nicer.  The clouds have great detail and definition, the sky is processed perfectly, the tree line is well exposed, and the rice fields themselves are well lit and the color vibrant.  I must say though, HDR processing by itself did not achieve these results.  HDR processing with advanced image processing both were required.

The final image is much nicer.  The clouds have great detail and definition, the sky is processed perfectly, the tree line is well exposed, and the rice fields themselves are well lit and the color vibrant.  I must say though, HDR processing by itself did not achieve these results.  HDR processing with advanced image processing both were required.

To capture HDR images you ideally want to set up on a tripod so you capture exactly the same scene.  If you have a modern and fast DSLR you can often get away with “auto-bracketing”, but it’s still good to learn this process using a tripod.

Expose your histogram for a balanced exposure.  When your histogram is as balanced as possible, note the value.  Now, DO NOT CHANGE THE APERTURE.  ONLY CHANGE THE SHUTTER SPEED when capturing HDR images.  Noting the histogram change the shutter speed to capture images above and below your reference image.  In the example above I captured three images, one stop apart.

Sometimes you’ll want to capture five images, sometimes seven or nine.  Usually 3-5 are adequate, but it really depends on the scene and how large the steps are between.  The closer the steps between, the more smooth the tonal range.  It’s all a trade off in time and effort, but each scene should be evaluated individually to determine how many images and how large the steps.  Only experience can tell you these values.

You can then use HDRsoft’s excellent PhotoMatrix or Adobe Photoshop's HDR feature to process the HDR images.  I use Photomatrix.  There are several advantages to Photomatrix, one of which is the ability for the program to line up images which were not captured perfectly.  By this, I mean if the frame shifted side/side or up/down a bit while handholding, Photomatrix can probably help line them up correctly during the processing.  We’re talking very small amounts here, not gross errors.  Photomatrix also includes a very good tonemapping program and Lightroom plug-in to help your workflow.

I’m not going to get into the actual HDR processing.  I’ll save that for a later date.  Photomatrix has an excellent tutorial and so does Adobe, and I’d recommend both.

For now, let’s take a look at some common HDR errors.  I’ll be using images I’ve used in the column previously, but now in a different context.

 

This image was captured at 12mm (full frame) and the camera was resting on the log to your left.  It was sitting right on top of the log.  Notice the clouds look weird?  Clouds move very fast.  Often over 100mph.  These clouds were moving towards me, and moved enough during the five captures to sort of blend together creating this weird effect.  The image is nice enough, but the clouds are just wrong.

This image was captured at 12mm (full frame) and the camera was resting on the log to your left.  It was sitting right on top of the log.  Notice the clouds look weird?  Clouds move very fast.  Often over 100mph.  These clouds were moving towards me, and moved enough during the five captures to sort of blend together creating this weird effect.  The image is nice enough, but the clouds are just wrong.

 

I’ve now turned 180 degrees.  Now the clouds are moving away from me at the same speed.  The effect however is different.  Great scene, weird clouds.  This happens with anything that moves.  Water, branches in the trees, people, cars, anything that moves.  If the scene has any movement at all, then HDR probably isn’t the best technique you could use.

I’ve now turned 180 degrees.  Now the clouds are moving away from me at the same speed.  The effect however is different.  Great scene, weird clouds.  This happens with anything that moves.  Water, branches in the trees, people, cars, anything that moves.  If the scene has any movement at all, then HDR probably isn’t the best technique you could use.

 

I’ve always liked this image.  Seven images combined.  I needed at least seven because the dynamic range from the very bright sky to the very shaded foreground was huge.  I probably should have used nine.  The clouds cooperated in this image.

I’ve always liked this image.  Seven images combined.  I needed at least seven because the dynamic range from the very bright sky to the very shaded foreground was huge.  I probably should have used nine.  The clouds cooperated in this image.

 

This image is a proper HDR image.  Everything came together like it should.  The clouds are right, the water perfect, and the tonal ranges make the image very attractive.  Remember I’ve said many times that we might take 1000 images and only get 4-5 really good ones from that 1000?  The same thing applies to HDR.  Just because you take the time to capture and process HDR, don’t think the process is magic and every image will look great.  Only some will, and the more experience you have evaluating scenes, the more keepers you’ll achieve.

This image is a proper HDR image.  Everything came together like it should.  The clouds are right, the water perfect, and the tonal ranges make the image very attractive.  Remember I’ve said many times that we might take 1000 images and only get 4-5 really good ones from that 1000?  The same thing applies to HDR.  Just because you take the time to capture and process HDR, don’t think the process is magic and every image will look great.  Only some will, and the more experience you have evaluating scenes, the more keepers you’ll achieve.

Remember these rules:

    • The scene should be evaluated for HDR.  Only scenes with a dynamic range that exceed that of the camera should be considered.
    • Shoot from a tripod, or at the minimum auto-bracketing.
    • Shoot in either manual (preferred) or Aperture Priority mode.  The only value that should change should be the shutter speed.
    • HDR process in Photomatrix or Photoshop.
    • Tone-map and use advanced processing techniques on the resulting image.
    • Not ALL HDR processed images will be keepers.

I hope this helps.  There are other techniques besides HDR and I’ll cover them in the near future.  Which technique you choose depends on your evaluation of the scene, available time, and desired effort you wish to deploy.