What Tone mapping settings to go for in HDR Post-processing?

Question

I have just recently started discovering the HDR side of photography and after seeing some really beautiful pictures, I decided to get the tools and perform it myself. While trying to post-process my three different exposure images in Photomatrix Pro 3, I would like to know what Tone mapping settings to go for in order to get the best results. I have tried quite a lot of times, but the image always gets overdone. Any suggestions on the settings are most welcome. I have attached my three images below, just in case someone wants to show me a good example of it.

Thanks.

Answer

Each image is different, so it's hard to say which settings will work. Many people use several HDR programs and try their images on each to see, for a particular scene, which one does the best job. I don't think it's a real science, mostly just fiddling with sliders.

It also depends on what look you're going for. Anywhere from natural, where there's hardly a hint of HDR, to surreal.

Looking at your images, I usually only do a set of three, but in this case I think you may need more, particularly to get more exposures which show your shadow detail. I think the result would be smoother if you'd done 5.

I never got the hang of Photomatix, so mainly use Nik HDR Efex as I thought it had more intuitive sliders and better presets to give me a head start, although the de-ghosting isn't always as good.

Any HDR program is going to have a main "strength" or "effect" slider that will raise the shadows and lower the highlights, so that what starts out looking like a "normal" image with deep shadows and light hightlights becomes more compressed to you can see detail in each. This slider basically takes you from natural to surreal. I start with that to get the overall effect right.

There will usually be a details slider that gives you more local contrast so you can see more detail.

If the image is too dark overall, I would raise the exposure, then possibly have to go back to the strength slider.

Then I would make small adjustments with black and white points or contrast. And finally adjust saturation.

Here is what I came up with quickly, using the "Details Enhancer" method of tone mapping (which is the only one I'm able to get any sort of decent result out of).

I boosted the strength to 100, raised saturation to 65. In "more options", I dropped the white point to keep the clouds from blowing out, and raised the black point a bit to raise the contrast of the image. I also brought up the temperature to warm it a bit.

The foreground is still fairly dark. I'm not sure what you were after.

If you haven't seen Trey Ratcliff's tutorial, it's a good place to start to learn about doing these.

Check more discussion of this question.

How do pseudo or fake HDR programs like Photomatix work?

Question

There are a few programs that can produce HDR-like results from only one input image. How do these work?

Answer

First of all it's important to understand the difference between HDR and tonemapping. HDR is a technique to capture images which contain a huge variety of brightness information. However most people lack high dynamic range monitors to show this information. If you simply scale the large range of brightnesses down to a smaller range, you end up with an image with very little contrast.

Tonemapping is a technique to maximise local contrast. Imagine you're adjusting the contrast of an image, after a certain point, as you increase contrast the darkest and lightest areas will hit pure black/white and you'll start to lose detail. Now imagine adjusting the contrast of each quarter of the image separately. You'll probably be able to push the contrast that much higher as the darkest and lightest parts of each quarter are not as far apart to begin with as the darkest and lightest parts of the whole image.

Now there's one further point to appreciate: dynamic range and noise are like opposites of each other. Technically they are inversely proportional to each other - the higher the noise the lower the dynamic range, and vice versa. So you can tonemap (increase local contrast) of any image, but if you start with a low dynamic range image, the tonemapped image will contain more noise.

The ability to produce "fake HDR images" is nothing to do with the extra range you get in raw images. It's because tonemapping has nothing to do with HDR. You can shove a standard 8 bit JPEG into photomatix, and you'll still get a similar result, just with more noise.

---

This is an image produced from three exposures using Photomatix:

Here I've taken the darkest RAW file and pulled up the shadows massively in Lightroom using the "fill light" slider:

Here I've taken the middle 8-bit JPEG image and loaded it straight into Photomatix (proving you don't need 12-14 bits to produce "HDR" images):

Three different sets of source data. Three different methods. Three rather similar results. There is no "HDR" - only tonemapping and local contrast adjustment. Source dynamic range only influences the level of noise in the final image, not what you can produce.

---

Here's another example to cement what I've said and help people get their heads round the relationship between HDR images and tonemapping. Here is the result of blending three exposures together:

It contains detail in both the sky, and in the shadow area of the pillars. If you had a high dynamic range image it would look amazing. As is is I've had to compress that large range down to fit within the low dynamic range of your typical monitor. This compression/scaling means the brightness values are very close together, leaving little contrast and a dull looking image.

Now let's increase the contrast globally:

Looks better, but we've lost all the detail in the sky, and a lot of detail in the shadows. Going back to the original, I divided the image up into 24 squares and increased the contrast in each square individually. This is the meaning of the term local in local contrast enhancement:

Now we have detail in the sky and the clouds. What's more it's starting to look a little "HDR" like! Some squares still have too much contrast, resulting in clipping of the highlights/shadows. If you made the squares smaller and smoothed the transition you'd eventually end up with a tonemapped image.

HDR/Tonemapping software (like Photomatix) uses a lot of fancy algorithms with lots of parameters to adjust but fundamentally all it does is local contrast enhancement.

Check more discussion of this question.

What is tone mapping? How does it relate to HDR?

Question

Whenever I read / hear about HDR (High Dynamic Range) photography, someone usually says something along the lines of "Actually, you're talking about tone mapping, not HDR."

Please can someone explain what Tone Mapping is, and how it relates to HDR?

Answer

An HDR image has a high dynamic range, which means a very large ratio between the brightest and darkest parts of the image. An HDR image on a normal (low dynamic range) monitor will actually look very flat:

This is because that huge range of brightnesses has to be compressed to fit into a much smaller range of brightnesses. This results in an overall lack of contrast, hence the flatness.

This image has a split personality, the skies are very bright and the subject much dimmer, if we could use all the monitor's brightness range for the sky, it would look pretty good:

But we'd totally lose our subject. Likewise if you used all the monitors brightness range for the subject it would also look good, but we'd totally lose the sky:

It would be great if we could combine them in some way, or carefully ration out the brightness range we have to work with so we make most use of it. This is where tonemapping comes in.

What tonemapping does is instead of mapping the whole image into the monitor's brightness range in one go, it adjusts the contrast locally so that each region of the image uses the whole range for maximum contrast (there's a bit more going on here, it depends on the tonemapping algorithm used). Here is the same image tonemapped:

The reason that tonemapping is not HDR is that you can tonemap a single low dynamic range image in order to make it more contrasty. The result looks similar but with much more noise in the shadows:

Disclaimer: for the love of God don't do this to your images!

This is an demonstration of the fact that dynamic range and noise are opposites, in fact dynamic range is usually defined in terms of the noise floor of an image. This is because there is a point at which any tonal differences in an image get lost in noise, so this defines the darkest thing you can image (which in tern with the brightest thing, defined by the point at which the signal clips) determines the dynamic range.

Check more discussion of this question.