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3. High Dynamic Range Photography - "HDR Look" and Pseudo HDR vs. HDR
Lightbox (41) Tags: digital-camera photography software Posted: Feb. 27, 2009 by Serge
In this part of the
article we'll be using
same set of images
Image exposure EV -2.64
Image exposure EV +2.64
Image exposure EV 0
applied to EV 0 image (Image -
Adjustments options of the
Photoshop main menu)
II. Steps in creating
pseudo HDR technique
using layer masks
1. Loading files into stack
(File - Scripts options
the main Photoshop menu)
2. Creating layer masks for
over- and underexposed
3. Applying image to layer
mask for overexposed
image (Image - Apply
Image options of the
Photoshop main menu)
4. Applying image to layer
mask for underexposed
image (Image - Apply
Image options of the
Photoshop main menu)
5. Resulting pseudo HDR
III. HDR Look
6. Pseudo HDR image
enhancements and local
7. Topaz Adjust Photoshop
8. Pseudo HDR image
"spicified" with Topaz Adjust
9. EV 0 with Topaz Adjust
spicified preset (with
additional heavy noise
One of the points I am trying to make in these articles is the distinction between real HDR and what has become known as HDR look. I believe it is necessary to understand pros and cons of various HDR tools and ultimately select the ones you need. To start, let's first take care of terminology: I would like to repeat what I wrote in the introductory article:
"Although there had been a number of attempts to achieve HDR, nowadays, one specific technique became predominant with digital photography (and the term HDR is used almost exclusively to refer to this technique). It consists of using several photographs taken with various exposures and produce a single high dynamic range image by combining them into one."
The key in the above definition is not just single image but single high
dynamic range image. We also talked about the so-called tonal mapping to
transform back HDR image into a new LDR image with hopefully better tonal
characteristics regarding under- and overexposed areas of the image. There are
two questions here:
- Do I really care about "true" HDR if there are other ways of achieving similar results?
- Do I care at all about HDR, if all I want is a "special" look that sometimes appears as a result of the HDR process?
By my experience and observations there are a lot of photographers that will
answer "I do not care" to both questions. Since the purpose of this series of
articles is to offer a simplified approach to HDR photography, I would like to
explore in more details the implications of both questions. In particular, I
believe that different photographers, while talking about HDR, may be
interested in reality in one of the following:
- HDR in the true meaning of this technique
- Alternative techniques that allow for producing images with better dynamic range
- Image post-processing (does not matter with or without "true" or "fake" HDR) resulting in what many people associate with HDR look.
Since we've been talking already a lot about "true" HDR (and will continue to do so in more reviews of HDR software), let's explore the last two issues: Alternative techniques and HDR "look."
Are there such techniques? Yes, there are many - obviously, some are better than others, some require additional skills, some require more time and some of them work well only in certain cases while others have more universal nature. Perhaps, if you have Photoshop, the easiest of such techniques is the Shadow/Highlight Adjustment tool. If you look at the result of using this tool, you will probably say that it's not good - and I will agree (most obvious problems are with highlights). At the same time, you will have to admit that dynamic range qualities of the original image have been improved. But what if you need high quality and your goal is to produce something quick? Or, what if your original photo is less problematic that the image used in this example?
Shadow/Highlight Adjustment is just one of the ways to deal with dynamic range problems, and there are many other techniques. Let me demonstrate one of them: it also relies on several source images. But I call it pseudo HDR since no HDR image is created here. Instead, this technique is just a way to borrow and merge pixels from different images using layer masks. It can be easily automated in Photoshop by creating an action with all necessary steps.
Steps involved are described in the side bar on the right (I am using Photoshop
CS3). To highlight some important details:
- Step 1 is just a convenient way of merging several pictures in one where each of the source images is in its own layer. The order of layers is important: overexposed image should be in the top layer, EV 0 image should be in the bottom layer.
- Layer masks (step 2) are created using Layer - Layer Mask - Reveal All options of the main menu.
- The order in which you fill layer masks with images is important: start with layer with overexposed image (step 3). This step is done using Image - Apply Image main menu options. Accept all default settings but check the Invert checkbox.
- Step 4 is similar to step 3, but this time you will work on underexposed image. Note that opposite to step 3, in step 4 you must not check the Invert checkbox.
- Since all the processing is done in layers, you can actually preview results as you go - meaning that there is no step 5. However, most likely, you will have to adjust the opacity of layers to your liking to get the pseudo HDR image.
If you examine the resulting image, you will see that in practical terms it's very close to what "true" HDR can offer (or, at least to what the implementation of the "true" HDR in some tools does). Note that I am not comparing the quality of resulting images; all I am saying here is that there are alternatives to HDR process that allow to some extend for improving the perceived dynamic range of images.
Have you ever read (or heard) things like "Oh, look at what I've done in Photoshop - looks like HDR, but it's not, and I did not even use several images!"? Well, I can assure you that whatever this statement refers to does not look like HDR. It looks like what some people (amazingly, there are more of them) believe is HDR. This sort of things leads to heated discussions where one side claims that HDR is an evil because it distorts reality and produces absolutely unnatural images, and the other side accuses the first of being retrogrades and clamping down on the freedom of artistic expression that HDR allegedly delivers.
I think the only reason debates like that even exist is that neither side knows what it is talking about. Indeed, there are techniques and tools that allow for processing of images to give them an appearance mistakenly believed to be a distinctive HDR look. For example, image #6 (see right side bar) is our old image #5 (pseudo HDR) with some color and local contrast enhancements. All this is done in Photoshop and these enhancements are still within limits of what most people would agree as natural.
By the way, the so-called local contrast enhancements are often at the foundation of the fake HDR look. The concept of this technique is that it increases "local" contrast in smaller regions, while preventing an increase in "global" contrast. Because of this, large scale details in shadows and highlights remain intact. One of the simplest (and best known) ways to increase local contrast is to use the Unsharp Mask filter where its "radius" is much larger (40 - 75) and the "amount" is much lower (10% - 20%) than what you would usually use for sharpening.
Some of local contrast techniques are quite complex and can be used as Photoshop actions. For example, here is a set of local contrast actions I found on the Internet (see inside the file for name of the action author) that fits almost all of my needs of this type.
For those who want quick results or in need of processing large number of images, the best way to achieve this goal is to use specialized tools or Photoshop plug-ins. My personal preference is Topaz Adjust - a $50 Photoshop plug-in you can open from the Filter menu option. For example, using this plug-in I managed to transform my pseudo HDR image into something that many photographers are striving for (see also side bar, image #8). The main reason I like Topaz Adjust is its simple and intuitive interface that nevertheless provides fine controls over the end result of your efforts.
To prove to you that there is no need at all for HDR (be it real or pseudo HDR) to produce that special HDR "look", and that this alleged HDR "look" can be produced from just one image, I prepared for you two more examples - see them on the left bar. Both examples are done with Topaz Adjust in seconds (literally) using "Spicify," one of the presets available in Adjust. Both examples include side-by-side comparisons of the original images (on the left) and processed images (on the right).
Side-by-side comparison of the explored so far
techniques related to dynamic range enhancements.
From left to right and top to bottom:
1. Ev 0 (neutral) Image
2. Photoshop HDR Merge (exposure blending) with
3. Photomatix HDR with Details Enhancer tone
4. Ev 0 Image with Shadow/Highlight tool applied
5. Pseudo HDR with Photoshop layer masking
and additional adjustments
6. Photomatix HDR with Tone Compressor tone
7. Ev 0 Image with Topaz Adjust “Spicify” preset
and additional heavy noise reduction (with Topaz)
8. Pseudo HDR with Photoshop layer masking and
Topaz Adjust “Spicify" preset
9. Photomatix “Extreme” tone mapping
The first photo is taken in Baptistry Church of St Mary in Arezzo, Italy and represents a typical setting appreciated so much by HDR "look" lovers - a dramatic semi-dark environment with many details and various textures that allow for showing the full potential of fake HDR look. Note that no special attempts were done to the image regarding its dynamic image. And, as you can see, the plug-in did not let me down - the result is quite consistent with what I planned to achieve. The second example produced with Topaz Adjust is to illustrate how this plug-in works with more conventional images - like the one of the street market in Arezzo. Again, it's quite consistent with what I expected to get.
Now it's time to look at what we've managed to achieve to far. There is a grid on the left side with nine images representing various tools and techniques we have used so far in the first three parts of the article. Select what you like more. Disclaimer: I realize that the size of images and vague references to "additional adjustments" does not provide a solid foundation for reliable comparison between the explored approaches to dynamic range enhancements. But remember - my goal is to give a simplified look at DR techniques. From this perspective, I have hoped to stay focused and provide more extensive overview in shorter time of what's available out there. As far as "additional enhancements" are concerned - they have not been extensive and relied mostly on curve, channel mixer and unsharp mask sharpening.
I want to stress that there are other tools for post-process photographs for the purposes of crafting fake HDR look. You may want to look at LucisArt 3 or Lucis Pro 6 Photoshop plug-ins. Personally, I believe that this plug-in prices (LucisArt 3 ED - $279, LucisArt 3 ED/SE - $379, Lucis Pro 6.0 - $595) do not correspond to the value that comes with them. But that's me, and I know a lot of people would disagree. Also, demo versions of Lucis plug-ins are not fully functional (opposite to Topaz products that you will able to use without any limitations for 30 days).
Finally, I would like to mention that HDR "look" is a hot topic right now (2009), and there are other products coming to the market. But my goal is to focus on real HDR tools - so, as far as fake stuff is concerned I stop here.