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Tone mapping is at the heart of what most people consider to be HDR photography. Although we have a wonderful array of tone mapping software at our finger tips, it isn't necessarily an easy task to create something beautiful with it.
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Gloucester Cathedral by Jimmy McIntyre
With row upon row of sliders screaming at us, it can be difficult to know what combination will get us our desired result. It's also a challenge learning the strengths and weakness of each HDR program. The more we can familiarise ourselves with the software, the more we'll be able to utilise it to its fullest.
In this article, I'll be giving advice that can be generalised to most tone mapping programs to some degree or another.
1.Create a Flat Image
No matter which software I use, I have one goal: create a flat image with as much detail as possible in all areas. I avoid, at all costs, creating or affecting contrast levels while tone mapping. Instead, all contrast adjustments are done in Photoshop, where I have complete control over every part of the image.
Any contrast adjustments while tone mapping will be applied across the image and could result in a loss of details.
This is the flat output after processing my exposures in Photomatix. All contrast adjustments and colour corrections were done in Photoshop afterwards.
2. Control Colour
Tone mapping has nothing to do with colour. It just so happens that HDR is often associated with over-saturated photos. The fact is, while some HDR programs handle colour extremely well, others don't. Photomatix does a terrible job of remapping colours, often leaving us with a cartoony, over-saturated scene. I always keep the saturation slider at around 35. The soul purpose of of the tone mapping software is to blend my exposures – I'll manage the rest in Photoshop.
3. Deal With Artifacts Beforehand
Again, as with colour control, each software varies in how they handle artifacts such as noise and chromatic aberration. For the most part, I will remove noise after the HDR process. However, I always minimise CA before tone mapping, where it will almost certainly be exaggerated. I open my brackets in Lightroom or ACR and enable ‘Lens Correction Profiles' and then check ‘Remove Chromatic Aberration'. I will then save the resultant files as Tiffs.
On some occasions it is important to apply noise removal before tone mapping, especially if the brackets were shot at a high ISO. In the image below, at Opera Garnier in Paris, the brackets were hand-held, limited to an ev spacing of 1 (-1,0,+1) and shot at ISO 400. Excessive noise was going to be an issue. Using Topaz Denoise to gently reduce noise first, I then saved the files as Tiffs and ran them through Photomatix to get a clean result.
Opera Garnier by Jimmy McIntyre
4. Create an Extra Exposure to Expand the Dynamic Range
We all know that it is important to make sure your brackets cover the range of light in a given scene. Sometimes, for whatever reason, we can't achieve that. We get home, look at our brackets and realise that our shadows are too dark or our highlights are blown out. In the image below you can see that my -2 exposure didn't have enough information in the sky.
If I run this set of images through an HDR program, the resultant shot will not have much information in the sky, either. This is because, although I'm inputting RAW or Tiff files, HDR programs cannot utilise the vast amount of data in these files and fill in the gaps. We can, on the other hand, rescue the situation. In Lightroom or ACR you can open your image and decrease the exposure by 2 stops. You will see information in the sky appear. Save this as a fourth exposure and run it through the tone mapping software.
Note: you must be shooting in RAW to do this.
An even quicker way of doing this is through the Highlights slider in both Lightroom and ACR. When you open your three exposures in ACR in order to remove CA, click on the lower exposure and slide the Highlights slider to the left. Again, you will see the information in the sky pop up without it affecting the rest of the image. Then you can save the three files and carry on as usual.
Same exposure as the shot before, but with the Highlights slider pushed to the left in ACR
Prambanan Temple by Jimmy McIntyre
5. Keep the EV Spacing Low
In other words, try not to create a big gap between exposures when you bracket. Ideally, you would cover the entire range of light in the scene and the exposures would have a difference of 1 (-3, -2, -1, 0, +1, +2, +3). That way there can be a smooth transition between highlights and shadows. If your ev spacing is too large, you may be lacking information that the tone mapping software needs.
In this particular example, I was dashing out the church when I saw this potential shot. In a rush, I fired off 3 brackets, -2, 0, +2. Then, to compensate for the extremely bright lights, I shot a -5 exposure. This was a gap of 3 stops from the next darkest exposure.
Since Photomatix didn't have enough information around the lights, which would have been supplied if I'd shot with an ev spacing of 1 all the way down to -5, it created a strange, murky halo.
I couldn't rescue this in Lightroon or ACR, sadly, so the final image had severely over-exposed areas and is not a good example of a balanced HDR.
Church vertorama by Jimmy McIntyre
So much to think about in the HDR process! The great thing is, after a bit of practice, the mindset required to consider all of this, and more, becomes ingrained. You tend to have a mental checklist that automatically ticks necessary procedures off as you work your way along the production of the image.
I hope that, even if you don't choose to implement these ideas into your own workflow, you stow them away somewhere in your mind because you never know when, or if, you might need them.