Understanding HDR part V – Understanding and handling tone mapping

Rothenburg ob der Tauber is one the most idyllic German medieval towns I have visited. Fot that reason I have been there three times. This split road is particularly lovely I think. Photo by: Jacob Surland, www.caughtinpixels.com

In the previous articles we have covered the theory behind HDR, and why it is necessary to take more than one shot. How to improve the image quality, by pushing the histogram to the right and various approaches to post-process HDR photos. This is fundamental knowledge to HDR photography.

If you did not read them, you might want to. You find them here:

The purpose and result of HDR software

Because you shoot several shots of the same scene, you have to use a tool to put them together. You can either do it manually, and blend the images, by stacking the photos in Photoshop or GIMP and then blend them into a final HDR photo using layer masks. Or you can use a tool that will do this automatically.

The automatic HDR software is probably the more common approach.

The problem of doing something, automatically is, that you are less in control, and the engine might not do want you want it do, or it will do more than you want it to do. Like in all other aspects of of life ‘there is no silver bullet’. There is no secret recipe, that will give you fantastic HDR photos, by pressing a button.

But making a fantastic HDR photo, does not have to be difficult, if you just know what to do, and have done a little practicing. I will help you understanding, what it is that you (need to) do.

As covered in part IV, the purpose of the HDR software is a two step process, first to merge the photos together to a 32-bit image file (the real HDR photo), and second to transform it into a 16-bit image, because you can’t see the 32-bit image properly. The 16-bit, is not really an HDR photo, but is usually referred to as the HDR, and this I also do, just bear in mind that the 32-bit image is technically the HDR photo.

A tone mapping algorithm will map the tones from 32-bit to 16-bit and a fusion algorithm will blend the photos.

The fusion algorithm does not have the same flexibility and artistic options as does the tone mapper, and for that reason I personally prefer to use a tone mapper, rather than use a less flexible fusion algorithm. But it is a matter of personal taste.

Tone mappers also come in many flavors, and to me, artistic flexibility is the most important thing.

Single exposure tone mapping

The tone mapper maps tones from one image to another, by passing the image through an algorithm. The merging of three images into the 32-bit HDR, does not have anything to do with the tone mapper itself.

You can take a single (well exposed) image, and put that through the tone mapper, and you will get a similar result, as had you used a 32-bit HDR photo. The viewer will see the photo, and recognize it, as what is commonly referred to as ‘an HDR photo’ (keeping in mind, that the only HDR really is the 32-bit image, that we can’t see properly).

Not all single exposure images gives great results in the tone mapping algorithm. It depends very much on how well exposed the image is.

A couple of examples of single exposures I have tone mapped:

University of Copenhagen

Lighthouse on the edge

To commoners these photos will look like HDR photos, because what is commonly referred to as HDR photos, really are tone mapped images. And the commoners, will not know the difference. I hope I have made it clear enough to you.

Side effects when tone mapping

Tone mapping is not without flaws, in particular if you push the gas pedal towards the floor. To me the tone mapper is a flexible tool, that you can bend, not necessarily to your will, but can bend into many interesting and artistic results, but if you are not careful, you can also get the worst image ever. This opens up for creativity and I do use this to great extend, and with great care.

Let’s walk through some of the common side effects from tone mapping.

Halos

Halos are bright edges that appears around darker areas, typically along the horizon. You will see a bright halo in the sky, like if the horizon was shining. You then have few options, either lift your foot from the gas pedal, and do a less strong tone mapping, or see if one of the sliders, helps you, without ruining what you have. The last option is to fix it later. You often end up in this situation, because the rest is looking nice, and that IS no problem to fix later.

Part V - Halo example

And if you look at the thumbnail, it is often even easier to spot the halo:

Part V - Halo example

Some halos are easy to spot. You can see them a million miles away, but others you don’t notice at first. A thing I have begun doing, to increase my ‘halo termination quote’, is to zoom out and get a very small image. This way, you can see large halos very easily. These can ruin a photo too, but be difficult to see, if you work close to a 100% zoom level.

Noise

Digital noise is a killer in tone mapping. Some tone mappers are worse than others in producing noise. But where does the noise come from? The noise already exists in the photos, it’s just not very visible, but when you apply the tone mapper the noise is enhanced, because one of the things that the tone mapper does, is to increase micro contrast. If you have even a little noise, the tone mapper will enhance that noise. This is particular bad in large even surfaces and areas, like ground or sky.

There are several ways to keep the noise levels under control:

  • Keep your ISO to as low as possible, when you shoot your photos.
  • Use noise reduction software before merging the shots to the 32-bit HDR photo. Adobe Lightroom Noise reduction is great for this, but also the built in noise reduction in Photomatix Pro also works great.
  • Use the “Exposure To The Right” technique, I mentioned in part III, The Histograms.
  • Try the sliders, to see if they help you.

In some cases it can be difficult control the noise levels, and you just have to solve the problem later. If you have to solve it later, you can:

  • Use noise reduction software on the final image. If the noise is nasty, you might not be able to carry it all the way to a clean photo. But, there is a road in the middle, that is acceptable. Some noise is acceptable, while other types of noise the eyes are not as forgiving with.
  • The original photos will have less visible noise, try and blend this with the tone mapped image. This obviously replaces the tone mapping effect, and that might be a compromise to you. You can try a 50% blend, and see if that takes away most of the noise, but leaves you with some tone mapping effect. It’s a flexible thing, and you probably want to do it locally.

Let’s look at the example of this photo:

Part V - Noise example

This really is nasty noise and it is problematic to get rid of, from the tone mapped image. However, what the tone mapping also does, is to enhance my stars. The stars are almost invisible in the original photos, and I have found no other way to extract them, as efficiently, as tone mapping does. But it comes with a price, the noise. The task now is to make a compromise, between the noise level, and keeping the stars.

You are caught between a rock and a hard place. The problem is, that the noise reduction software, will also remove some of the stars. I chose this level of noise and stars:

Part V - Accept some noise

It is a compromise. This noise will not be particularly noticeable, even in a large print. To much noise reduction will take out details and soften the image, too little will ruin the image with too much noise. It is a balance.

Some people switch their HDR Software/tone mapper because of the noise. Photomatix is known for it’s bad noise levels, but if you know what to do, you can keep it under control and it is no big problem. I personally prefer the visual flexibility that Photomatix offers, and then handle the noise. It is the final result that counts.

Stormy Clouds

Dark stormy clouds are one of the easiest ways to spot (badly) processed HDR photos. While a beginner might think “Wauv”, because you suddenly get a very dramatic sky, you do not want to have a too stormy sky, if you want to have a great result. It must blend in nicely with the rest of the scene.

These clouds are too much:

Part V - Stomy and blown outs

In a photo like this, I would use the sky from one of the originals, like this:

part V - Stormy clouds fixed

Blown outs

You also have to look out for blown out highlights. Try to move around the sliders, to avoid this situation. If the result, really is, what you want, then you must fix it later in the process.

Some times only one of the colors blow out. I often have yellow splashes in my photos, telling me, that the red is blown out. This I usually fix later in the process, by mixing one of the originals back in those areas. Typically this happens around street lamps and other light sources. The principle is the same as fixing the sky in the example above.

The tone mapper can also be used “on itself”. When you tone map the 32-bit HDR photo, you get a 16-bit image as a result, this image, you can put into the tone mapper once more, and you get a “double tone mapped” image. While the double tone mapped images can get really funky, all of the nasty side effects explode too, and if you are not careful, it will blow out your highlights too.

Double tone maps, can only be used gently in a mixture with the original exposures and the single tone mapped image.

Over saturation

The tone mapper can increase saturation quite a bit. My photos are very saturated – just to the brink of ‘too saturated’. That’s because I like it that way, and I know I have gone over the top a few times. An over saturated image is not good, you do not want to go there. Be careful on the saturation slider.

The ‘grey’ look

This is a very common side effect from making HDRs and many people don’t know realize it and don’t know how to fix it. In this example (which is a single exposure, that I tone mapped), the sky has lost all of it’s blue color in the left one:

Part V - The grey look

To fix this issue I used the original RAW file, and made virtual copy in Lightroom, and played around with the sliders until I had the sky I wanted, and then I blended that sky into the ‘grey’ version.

Another example:

Part V - The grey look example twoAnd this is the final image including process flow in Photoshop:

Part V - Removing grey look

Notice how the colors start popping, and that the grey look disappears.

And final touches in Lightroom to bring back the blue sky:

Part V - Removing grey look step 2

Removing the grey look, truly transforms the image. These two are very colorful examples, but they had not necessarily needed to be that colorful.

The softness

Another side effect is softness. This is fairly easy to fix, you just need to use some sharpness and contrast. In Adobe Lightroom this can be done by adding Sharpness, Clarity and/or Contrast, in Photoshop you can also add contrast this way:

Part V - fixing softness

No black in HDR photos?

This is in the same category as softness. Tone mapping can give both too much and too little contrast even in the same image. The stormy clouds from before had too much contrast, while the ground in the same image had too little contrast. And this really is the core of the reason why, you can not apply I tone mapping, and then expect to get a final image. You need the image processed different, in different areas.

When you apply contrast, even if only locally, you start adding black back into the photo, and this is a very important step. A photo without black, will look flat. You do not want that.

What you get from tone mapping must be processed further, to get a better result. And working with contrast, both removing and adding, is a very central part of this process. 

What HDR software to use?

I have tried various HDR software both for Mac and PC, but for me, what it comes down to, is how many artistic options do I have? How well does it integrate into my workflow? What is the performance?

In the end, what is important to me, is what I can get out of the software, in the final image. I have an overall processing workflow that looks like this:

  1. Prepare images in Lightroom (white balance, noise reduction, lens correction and maybe more).
  2. Process the images in HDR software.
  3. Load HDR result image and the original photos into Photoshop as layers.
  4. Blend the layers to get a “clean” image, rid of HDR artifacts, halos, noise etc.
  5. Apply more effects using tools like Topaz, Nik Collection or OnOne.
  6. Reimport the image into Lightroom and do finishing touches there.

When I evaluate the HDR software that I use, I evaluate in this context. It’s just one step out of several, and it’s certainly not the last.

From the various pieces of HDR Software, I have tried, there really only are only two that I keep around, and I use the one for 98% of my HDR images. I use Photomatix Pro 5 for 98% of the images, and I use HDR Efex Pro 2 (a part of Nik Collection, from Google), for the last 2%. The last 2% are mostly for giving the alternative a second (third and fourth) chance or if for some reason Photomatix fails to produce something that I like.

HDR Efex Pro 2

There is no doubt, that the user interface of HDR Efex Pro 2 is very nice and has many sliders. There is a lot of control on many parts of the processing, but the creative sliders are not worth a lot – they are close to useless:

Part V - HDR Software 1Having sliders with 4 to 6 stops is not a lot of options, why not make them slide softly from one to the other? To me, these are the options for the creativity and they just doesn’t cut it. More than half of the positions bring your photo into the realm where you do not want to bring your photo. This is the far extreme:

Part V - HDR Software 2

This effect you see in this example is what I do not like about HDR Efex Pro 2, it keeps sneaking in. As soon as I try to go a little more creative, this is the effect that starts appearing, and I do not like it.

In this photos, it is the same effect sneaking in, and all I want to do, is enhance the texture on the building:

Part v - HDR Efex Pro 2 - 1

This I would never use in final photo, it looks cheasy and like a bad HDR photo.

That said, you do have a very good control of the contrast, highlights and shadows in various ways. And for a photo in a fairly realistic world HDR Efex Pro 2 does a very nice job. I love the workings and user interface of the program, but I do find it a bit on the slow side.

The tool has got some “finishing touches”, which indicate, that you can produce final results in this tool, but DO NOT let yourself be fooled! You only get the 80% in the tool, you still need to get the last 20% in Photoshop or Gimp.

The noise levels are kept under control. The noise reduction is probably a part of the merge procedure. If you use Noise reduction in Photomatix, you also have noise levels under control.

Halos appear different in HDR Efex Pro 2, than they do in Photomatix. You don’t get the huge nasty halos, but you get small lines along the horizon. But don’t be fooled, these might prove be at even harder to to remove than larger halos.

What I like

  • Produces really nice results, within a natural realm.
  • Nice user interface.
  • Low noise levels – not non-existent, just low.
  • Good control of contrast, shadows, highlights
  • Good integrations into: Lightroom, Photoshop and Bridge.
  • It is not prone to make the same artifacts as Photomatix, such as Softness and The Grey Look.

What I don’t like

  • Not good on the artistic side
  • Keeps sneaking a special kind of style of texture into the photos, that gives a cheap HDR look, that is hard to get rid of.
  • Makes small halos that are difficult fix.
  • A bit on the slow side.

Photomatix Pro 5

Photomatix Pro is one of the pioneering HDR software engines on the market. It’s both famous and infamous. It’s a very flexible tool, that can produce many different results, both good and bad.

The user interface is not as nice as HDR Efex Pro 2. It looks a bit old and out-dated.

There are a number of HDR engines built in, both fusion and tone mapping.

Compared to HDR Efex Pro 2 there are fewer sliders in Photomatix Pro, but you still have many ways of controlling the contrast, which is the important thing. Some of the sliders a bit magic and mysterious, but that is what creates the magic I guess.

There are a number of processing engines built into Photomatix, the one that gives most flexibility for creativity is the “Tone mapping->Details Enhancer”.

Let’s have a look at the same image, as processed in HDR Efex Pro 2, just processed in Photomatix Pro. First the single tone mapped image (btw: To me it seems that HDR Efex Pro 2, does not give the additional effect by double tone mapping):

Part v - Photomatix Pro - Single tone mapped

I do like this texture. It does not have the same cheap HDR effect, as the one HDR Efex Pro 2 produced. And then the double tone mapped:

Part v - Photomatix Pro - Double Tone mapped

This is the magic, that Photomatix does. It creates nice texture. You only use this double tone mapped image lightly, because of all the nasty artifacts, but this effect, can put magic into your photos. Just use it with care.

Photomatix produces some artifacts, and that is what it is infamous for. The noise can get out of control, but if you use either the built in noise reduction or use Lightroom’s noise reduction before exporting to Photomatix Pro, you will be alright.

Halos come are common, but there are some tricks to get rid of the too. The “Smooth Hightlighs” can be useful, not always, but often:

Part v - Photomatix Pro - Halos 1

And then if I increase the “Smooth Highlights” to 80, it helps a lot, it also takes some of the “greyness” out of the photo. What’s bad though, is it also takes out a lot of the texture effect, which I really liked.

Part v - Photomatix Pro - Halos 2

In a case like this, I would make one of each, and mix them to the final photo, along with the original 3 shots I have.

What I like

  • Good artistic flexibility
  • Produces really nice results, both within the natural realm and the more creative realm.
  • Good built in noise reduction – just remember to use it.
  • Good control of contrast, shadows, highlights.
  • Good integrations into: Lightroom, but it supports drag’n’drop.

What I don’t like

  • The user interface is out-dated.
  • Makes large halos.
  • Creates a grey look
  • Creates a softness.

Conclusion

There is a reason, that I stick to Photomatix Pro, despite the rather severe artifacts it generates. It has got a flexibility and magic, that the others don’t have. The final results are much better, from an artistic point of view. But! There certainly is room for improvement. The tool itself looks outdated, and it must be possible to adjust the algorithm, to make fewer of these artifacts.

I will never get a workflow, skipping what I do in Photoshop. It’s hand crafted HDR photos I do, not press a button HDR’s. And for that reason, all artifacts, can be overcome and fixed.

A seriously better HDR program, will of course cut a little bit of the post-processing time, but not really a lot. When you have tried to remove halos, bringing back the colors (aka removing the grey look), removing the softness, you realize, that this really is very simple and easy. You learn what to do, and it is quite easy and fast.

What I will never give up on, is the artistic flexibility.

Wrapping up this series of blog posts

So this wraps up my five articles on understanding HDR photography better. I hope that you learned something. If you have any questions, please leave them in the comments.

Thanks for reading the articles!

Further reading

If you want something more to read, these are good points to continue:

5 thoughts on “Understanding HDR part V – Understanding and handling tone mapping

  1. The biggest problem with Photomatix is all that softness that can’t be fixed with sharpening and other tools (something that has no detail can’t get details back no matter how much you choose to sharpen it). None of the examples in your HDR series show a single image that is sharp and they all look “Photomatixy”.

    Therefor manual exposure blending and luminosity masks is the way to go if one want to increase the DR of a scene. If you want all that crazy texture use topaz plugins and masks in Photoshop.

    1. Hi Tom, this I only partly agree on. True that softness is an possible outcome of photomatix, but look at my photos, I do not have softness. You just have to know how to fix it. And sharpening is not the only answer. I think I will extend this post on how to handle softness. Thanks for the input.
      –Jacob

      1. Hi, I don’t agree. 🙂

        In some there are less softness but the image with the masts on the ships is a great example for when Photomatix and any auto-HDR app get some real problems. My previous comment was a bit harsh by the way but i really think that you (and your readers) would benefit more from exposure blending and luminosity masks and the techniques involved with that.

        1. Hi Tom,
          My point is that you show never use an image directly from any HDR software. Auto HDR software does not create final images. There’s hand work that has to be done afterwards. I have looked into luminosity masks earlier, and will do again. However I am not particularly fond of HDR made in luminosity masks. They get too sterile too my taste. But that is a matter of taste and taste is different. I believe that the softness, can be used as an asset, if you use it with care. The bigger problem I had on the masts you refer to was halos, and the softness you see does not come from Photomatix, because I had to mask that out. That comes from the raw file. I will look into luminosity masks again, not only because you insist 😉 but also because I have come across other usages it is recommended for. Thanks for the feedback – there will be some posting on various usages go the luminosity masks some time in the future. –Jacob

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