Understanding HDR and Tone Mapping

January 30

8 min. to read

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In this post we'll go through the differences and explain what tone mapping really is.

Photographers commonly confuse HDR and tone mapping. While these two techniques are definitely related, they aren’t the same thing. HDR stands for High Dynamic Range and is a process through which multiple images are combined to increase the final image’s overall dynamic range using an HDR editor like Aurora HDR. But this doesn’t mean that the image you get is necessarily oversaturated and high-contrast — things that HDR is usually associated with. It just means that the image has a lot of detail that you can work with.

This detail can be brought out of the image using a process known as — you guessed it — tone mapping.

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A little more about HDR

Before we move on to the question What is tone mapping? let’s understand a little more about HDR photography.Understanding HDR and Tone Mapping Image1

Modern cameras, even with their large fancy sensors, aren’t able to capture as much detail as the human eye can see in any given scene. This means that even with the sharpest, highest-resolution photos, a scene can’t be depicted realistically in a single frame because the dynamic range just isn’t there.

In order to capture more detail, you need to take multiple photos of the same scene and merge them. But you can’t merge the same photo, as it would have no effect on the dynamic range. What you need to do is take one photo that has a balanced exposure and then take more photos that are underexposed and overexposed. When you merge these photos, what you end up with is much more detail both in the highlights and in the shadows.

Now you have a photo with a lot of detail but one that isn’t particularly contrast-y or true to life. This is where tone mapping algorithms come in.

All about tonal values

Dynamic tone mapping is used to make flat HDR images look punchy and full of detail. Tone mapping deals with reducing the tonal values within an image to make them suitable to be viewed on a digital screen. For example, an HDR photo that has a 100,000:1 dynamic range needs to undergo tone mapping so that the tonal values fall between 1 and 255.Understanding HDR and Tone Mapping Image2

This dynamic tone mapping is important as it makes the image look realistic on most modern displays. These displays simply cannot reproduce the high dynamic range that your file may end up with after merging multiple photos, so dynamic tone mapping is a vital step to reduce the tonal variation in such photos.

There are two types of tone mapping algorithms:

Global operators

Each pixel in an image is mapped based on its global characteristics in this method, regardless of where in the image it falls. This means that the position of the pixel in a light or dark portion of the image isn’t taken into account. While this type of tone mapping is fast, what it leaves you with is a rather flat image.

Local operators

In contrast to global operators, local operators do take note of a pixel’s position in the light or dark areas of an image. Pixels are then treated according to their spatial characteristics and much more detail is eked out of them as a result. The final image is more pleasing to the eye and has more visible detail with this local tone mapping technique, but unsurprisingly it takes more time to process.

Understanding HDR and Tone Mapping Image3

There are many powerful image editors that allow you to use these tone mapping techniques to create stunning HDR images. If you’re interested in doing some iPhone HDR photography and don’t want to take multiple photos, some editors can even create convincing HDR-like photos from single images.

For the best results, shoot RAW

Let’s get one more thing out of the way. Yes, it’s true that you don’t need to shoot in RAW to create HDR images. It’s even true that you don’t need multiple exposures to tone map an image to look like an HDR photo. But it’s also true that if you shoot in RAW, you’ll have much, much more information in your file to work with.

One of the best HDR editors that can help you achieve great results is Aurora HDR. Aurora is known for its realistic results that you don’t even have to work too hard to get. Presets can do most of the work for you as soon as you merge your different exposures, and then there are deep manual controls to tweak images to your heart’s content.

Understanding HDR and Tone Mapping Image4

As you now understand, tone mapping is simply a part of HDR processing. You can perform tone mapping on single images as well as on HDR images created from multiple merged images. Remember that you’ll get much more detail in your final image if you shoot in RAW and if you merge at least two images with different exposures. But no matter how you plan to get started, don’t forget to give Aurora HDR a try as it can help you achieve excellent results with minimal effort and in very little time.

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