Monthly Archives: January 2018

HDR – a misunderstood technique?

Sunrise over Helenevik in Mölndal, Sweden.

HDR means High Dynamic Range. It’s a technique that (in my opinion undeservedly) has a pretty bad reputation. You often see HDR images that are overprocessed with high local contrast and low global contrast, which creates a surrealistic look to the photos. It may be just what you’re after, but more often than not it isn’t, I’d say. But despite this HDR is actually a very useful technique, even if you’re not looking for the typical HDR look. That look comes mainly for a process called “tone mapping”, and that can actually be avoided altogether if you like, even while enjoying the benefits of HDR photography.

Let’s start with a quick introduction. HDR stands for “High Dynamic Range”, so it’s obviously a photo with a greater dynamic range than a normal photo. A camera’s dynamic range decides how big a difference it can be between the darkest and the lightest point in a photo. Since cameras have a limited dynamic range it means they have a hard time correctly capturing scenes where there’s a huge difference between the brightest and the darkest areas of the image, for example if you’ve got a bright light source and heavily shaded areas in the photo. In this situation you need to choose whether to expose for the highlights or for the shadows. If you expose for the highlights you avoid blowing them out, but in return the shadow areas will be way too dark. If you increase the exposure in the image in postprocessing, the shadow areas will become noisy instead. If you choose to expose for the shadow areas you can render them without noise, but the highlight areas will be hopelessly blown out and impossible to recover.

This is where the HDR technique comes in – it can be used to practically increase the camera’s dynamic range almost indefinitely. What you do is that you take multiple images where you change the exposure value between them, usually by choosing different exposure times. Then you combine these images – you take the brighter areas from the underexposed photos, and the darker areas from the overexposed photos. There are different ways of doing this, and I’ll soon describe a couple. But first a short paragraph on how to actually take the photos.

First of all it’s highly recommended to use a stable tripod. If the camera moves during or between the exposures the results will not be as good. For the same reason it’s recommended to use a remote control or wire trigger for the camera. Most modern cameras have a number of options to assist in taking HDR pictures. There’s often a built-in HDR mode, but I prefer to avoid this as it gives a JPEG image where you get much less control over the result yourself. What I use is a function in the camera called “Auto Exposure Bracketing”, AEB. This allows me to set how many photos I want to take (often you can choose from 2, 3, 5, 7 or 9 photos) and just how big a difference in exposure there should be between them. Exactly what to choose depends on the scene in question, but a good starting point is to do three photos with 2-3 stops of exposure in between them. How exactly to do this differs depending on which camera you have – see your instruction manual or google “HDR” and your camera’s model name and I’m sure you’ll find instructions. As always I recommend that you only shoot in RAW so you have the maximum amount of data to work with.

Then when you have your photos on the computer what remains is to actually combine the separate exposures into one. There’s a multitude of software dedicated to this purpose. Popular HDR software includes Nik HDR Efex Pro which is a part of the Google Nik Collection (and I think it’s very easy to work with and free as well), Photomatix, and Aurora HDR. These applications are popular because they’re generally easy to work with and can very quickly give really dramatic results. It’s also easy to take them too far and get images with that typical HDR look that I mentioned earlier. I prefer a way of working that gives me more control and allows me to use my regular editing techniques to produce HDR images.

I like the built-in HDR function in Lightroom (or Photoshop if you prefer that). Many look down on these as simple because they don’t offer the same possibilities to quickly create a dramatic look, but in fact that’s what makes them the opposite of simple. I like them because they give you all the possibilities to edit the photo the way you normally would, but with access to the expanded dynamic range that lets you pull down highlights and lift shadows without noise in a way you just couldn’t in a regular photo. The photo at the start of this post is created entirely in Lightroom using the HDR function, and I will now show you the complete process.

Here’s a view in Lightroom that shows my seven exposures completely unedited, from underexposed to overexposed:

What you do next is that you select all fo the photos, and either right click and go to “Photo Merge” -> “HDR” or press CTRL+H on your keyboard:

That brings you to this dialog:

“Auto Align” makes Lightroom automatically align the photos in case the camera moved a little between exposures. “Auto settings” basically does the same as pressing “auto” in the basic panel of Lightroom, and I always leave that unchecked. Deghosting is a function to handle any objects in the photo that might have moved in between exposures. You can select the different levels of deghosting and if you’ve checked “Show Deghost Overlay” then Lightroom will show you a red overlay where it will apply deghosting. When you’re happy you just click “Merge” to merge the photos. The merge job will be added to the processing queue in Lightroom and when that’s done you’ll have a completely new image. A tip if you want to work faster and you know you want the same HDR settings as the last time you performed a merge is that you can hold down SHIFT when selecting to HDR merge. This will make Lightroom skip the dialog altogether. Here’s the result of the merge:

As you can see the photo is still prety undramatic and looks roughly like the normal exposure from the set used to create it, but we’re going to solve that in the next step. What makes this new image different from the rest is that Lightroom has taken all of the RAW files you captured and combined them into a new RAW file in the DNG format, but this file is 32-bit and contains data from all of the photos you chose to merge. It has a huge dynamic range – it’s an HDR image, simply put. Now we can move on and edit this image just the same way we would edit any RAW file. You can add profile corrections, change the white balance, and adjust anything else you like. You can also export the image to Lightroom and other software, just like with a RAW file.

The editing on my photo is done completely in Lightroom and is actually pretty simple. I started by checking the boxes for profile corrections and chromatic aberration, which I always do (and usually that’s enough, but for some photos you need to do manual corrections as well):

There are some global adjustments of the basic settings and the tone curve as well:

Also some adjustments in the HSL panel:

And the rest of the editing is done with filters and brushes in Lightroom. First, a gradient filter to darken the sky and the sun, and increase the contrast in those parts:

Notice how I’ve used the “Range Mask: Luminance” to make sure the filter only affects the bright sky, not the dark trees also covered by it. This is a very useful technique for darkening a bright sky where there are other objects breaking the skyline. Next, a gradient filter to add some blue in the sky:

The next step was to paint generously with a brush to add exposure and increase contrast in the foreground:

The red field shows where I’ve applied the brush. After that, I added another brush to increase the color in the plants in the foreground:

And that’s it! After these adjustments the end result looks like this:

If you prefer not to use in Lightroom but use Photoshop all the way, you can do the same in Photoshop. I recommend using the “Merge to HDR Pro” function and selecting 32 bit mode:

Then you can work with the photo just like any other photo, except that you have a huge dynamic range to work with.

Do you have any opinions about HDR techniques, photo editing, or just opinions in general? Do leave a comment below!

Long exposures – how long?

An ocean cove in Nolvik outside Gothenburg, Sweden, is serenely lit by the cold, blue moonlight.

The photo above is taken in the deepest, darkest Swedish winter night, with only the moonlight helping me. To get it so bright and sharp it’s necessary that the shutter remains open for a long period of time, to gather enough light. In this case, the exposure time was roughly ten minutes. To do this you put the camera on as stable a tripod as you can, and you use the mode called “Bulb Mode”, where you manually decide how long the shutter stays open – the camera will keep the shutter open for as long as the shutter button is depressed. It helps a lot to have a remote control in this scenario.

When I posted the photo to a Facebook group I was asked the question how I knew that I needed to expose for ten minutes and no more or less. When in Bulb Mode with long exposures, you can’t use the camera’s light meter to help you, but there’s a simple trick that can be used. If you put the camera back in manual mode (with the same aperture setting, of course) you can raise the ISO number and measure the light, as well as to a test exposure to see that it looks good. Then you can calculate the exposure time at ISO 100 by counting backwards, so to speak.

Let’s say I raised the ISO to 1600 and got a correct exposure in 13 seconds. Since ISO 1600 means an amplification of the light by 16 times (or four stops), this means that the same exposure at ISO 100 would be gotten in 13 seconds * 16 = 208 seconds, or roughly three and a half minutes.

In this specific case I used ISO 6400 and got a correct exposure in 9 seconds. So the correct exposure at ISO 100 is therefore 9 * 64 = 576 seconds or just over nine and a half minutes. And here’s another trick if you don’t have a calculator with you (or, let’s be honest, can’t be bothered to get your cell phone out to make the calculation). Since 64 seconds is roughly a minute, you can say that every second of exposure at ISO 6400 equals roughly a minute of exposure at ISO 100!