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I have come across these techniques recently but can't see the point of doing one with a software and another manually with a photoshop tool. Basically what we are achieving is "expected" exposure for the complete picture with different pictures combined in different exposure settings.

IF the method is almost same why different name? In one way digital blending looks similar to combining of two different pictures to me.

Kindly correct me if my point of view is wrong. Thank you.

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Generally, digital blending involves the use of a generic image editing software and, via layers and transparency masks, selecting the properly exposed parts of each image.

On the other hand, HDR is an automated process in which the total dynamic range of the image is extended beyond the "normal" scale to contain all the tones of the scene. The HDR image is then tonemapped to reduce its dynamic range while preserving the "dynamic" of the image.

In short, they try to achieve the same goal (correct exposure of highly dynamic images) but with different processes and results. HDR usually depends largely on the tonemapping algorithm used, and can produce realistic as well as fairly innatural "painting-like" images. It usually also have the side effect of increasing the noise.

  • HDR, or High Dynamic Range photography is much broader than the narrow definition you have given it. It includes what Gustave LeGray did to produce seascapes in the 1850s. It includes what Ansel Adams raised to a high art form in the darkroom in the mid-20th century. One type of HDR photography is to use an automated process to tonemap an image, but it is not the only way to do HDR imaging. Digital Blending is also considered HDR Imaging. – Michael C Dec 4 '13 at 15:27
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    @MichaelClark mh, I don't know exactly the history of HDR imaging, but I took for granted the process that nowadays is typically used, I think the OP also intended that one. But thank you for the information, I'll read something more about it :) – clabacchio Dec 4 '13 at 17:20
  • @clabacchio What do we exactly mean by the term "tonemapping"? – Amrit Dec 4 '13 at 18:13
  • @Amritpal you'll find more information on Google, but it basically refers to the process of "shrinking" the extended dynamic range into the normal color depth. You could just make a multiplication, but you'll probably get a dull image, due to the limited contrast. It's not an exact science, and there are various algorithms that give very different outputs. – clabacchio Dec 4 '13 at 18:26
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    Tonemapping also was around during the days of analog (film) photography. Dodging and burning are two ways of tonemapping. So is altering the amount of time the photosensitive paper is exposed in the darkroom, as the highlights and shadows of an image will be altered by non-linear amounts. – Michael C Dec 4 '13 at 20:42
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High Dynamic Range Imaging (HDR) has been around in one form or another since the 1850s. Gustave LeGray took multiple exposures of seascapes and combined them to render both the brighter sky and the darker water/seashore in the same print. In the mid-20th century Ansel Adams and others used dodging and burning, or what we call manual tone mapping, to raise the technique to a high art form.

Unfortunately, most people seem to think HDR means only the recent development of making a high-dynamic-range luminance or light map from multiple digital images exposed at different values using only global image operations (across the entire image), and then tone mapping this result. This type of digital global HDR was first introduced in 1993 resulting in a mathematical theory of differently exposed pictures of the same subject matter that was published in 1995 by Steve Mann and Rosalind Picard.

What is known today as Digital Blending is one way to accomplish High Dynamic Range Imaging.

  • Digital Blending takes different parts of several varying exposures of a scene and uses the properly exposed parts of each to create a new image in such a way that different parts of the scene that would be too far apart dynamically to display in a medium of limited dynamic range (such as a computer monitor or print) can be displayed in the limited dynamic range of that medium. It does so without creating a large floating-point file and the resulting need for tone mapping.
  • Another way to do High Dynamic range imaging is the process commonly referred to as HDR that has evolved from the work of Mann & Picard described above. It makes a high-dynamic-range luminance or light map from multiple digital images exposed at different values using only global image operations (across the entire image). The result is often a 32-bit floating point 'image' that no monitor or printer is capable of rendering. (Even when you open a 12-bit or 14-bit 'raw' file in your photo application on the computer, what you see on the screen is an 8-bit rendering of the demosaiced raw file, not the actual monochromatic Bayer-filtered 14-bit file. As you change the settings and sliders the 'raw' data is remapped and rendered again in 8 bits per color channel). It must then be tone mapped by reducing overall contrast while preserving local contrast to fit into the dynamic range of the display medium. This often leads to artifacts in the transitions between areas of high contrast.
  • There are an almost countless number of other processes used to produce High Dynamic Range Imaging, including those used in the analog (film) age of photography.

Each technique uses different approaches to the problem of a scene with more dynamic range than our current technology can reproduce using conventional techniques. Which one, if any, you choose to use should be based on what you wish the final result to look like as well as which fits your workflow the best.

See the halo around the balloon in the picture below? That is the result of global tone mapping of a single exposure to make the much darker balloon closer in brightness to the brighter sky. If I had used other techniques, such as digital blending, exposure fusion, or even manual cut and paste from different layers developed at varying amounts of brightness then the sky would remain the same brightness all the way to the edge of the balloon but the boundary between the sky and balloon might look like the balloon was cut from another picture and pasted onto the picture of the sky.

Tone mapped balloon

For further reading:
http://en.wikipedia.org/wiki/High_dynamic_range_imaging
http://en.wikipedia.org/wiki/Tone_mapping
http://en.wikipedia.org/wiki/Zone_System
http://en.wikipedia.org/wiki/Dodging_and_burning

  • Thanks for the history on HDR. :) But I want to know what's the difference btw both if both are in a way same? Why two different terms? – Amrit Dec 4 '13 at 18:16
  • The two different terms are for two different ways of combining information from multiple images to create a single image. – Michael C Dec 4 '13 at 20:39
  • I guess you can digital blend any image. Whether it's a really compressed jpg or just straight out of the camera. Generally, HDR involves using RAW images, resulting in a higher dynamic range of colours and contrast. But, if you're blending/layering images, you could call it blending. I guess it's like mixing cake mix or muffin mix. It's still cake mixing, but you get different results. – BBking Dec 5 '13 at 0:17
  • Except in your analogy you are applying the same process to different ingredients. In the case of Blending vs. HDR you are applying a different process to the same ingredients. – Michael C Dec 5 '13 at 0:28
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    @BBking "Generally, HDR involves using RAW images..." It does now, but when digitally combining multiple images to create a floating bit light map first started to be referred to as HDR (a term that already existed in reference to other techniques) it was primarily a technique applied to JPEG images or, if you really wanted to be exotic, 16 bit TIFFs. – Michael C Oct 10 '14 at 1:42
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High Dynamic Range (HDR) is the result of combining multiple images (the how varies) to get a single image that has more dynamic range than is normally possible in a single shot. There are several ways to do this, one is via tonemapping, which is what most people think of when they hear HDR and another is to mask it with layers. Each offers their own looks, have their own pros/cons, but are also both HDR.

There's a good, albeit long, discussion about HDR on youtube.

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