ProjectVISUAL

One of the necessities of creating pseudo-High Dynamic Range photographs is having multiple exposures of the same shot. This gives us the full tonal range of a natural scene needed to blend a HDR together. Blending is followed by tone mapping, which maps the colours contained in the dynamic range of the HDR to a rough set of similar colours that can then be displayed on monitors or any equipment that doesn’t have the full dynamic range to view the HDR in its true form properly. The question that follows then is how many different exposures do you need to take? And across how wide a range? ±1EV? ±2EV? Some people might go as far as ±4EV to be sure they capture every single shadow and light. Now while combining the metered image with 2, 4 or 6 exposures will give us a higher dynamic range image, I wanted to see how well the HDR process works using just a metered image (i.e. at 0EV) along with just two differently exposed duplicates; taken at ±1EV, ±2EV and ±4EV. For this example I’ve used Photomatix to create the mock HDR.

Here is each exposure as taken from the single RAW image in Photoshop (I’ve said it before – I never have a tripod with me so taking 3 or more RAW shots in near perfect alignment is impossible for me!). The exposures range from -4EV to +4EV with the metered image sitting in between them.

1. The Original (Metered) Photograph
First things first. Below is the original shot saved as a jpg from the RAW. As you can see the shot is generally a little over-exposed (the sky very) and most features are looking a little bland. A bit a post-processing is necessary me thinks.

2. Photomatix Using Just The RAW File
So the first step in this experiment is to run the single RAW image, no multiple exposures, through Photomatix and try to keep everything looking at least half realistic: The Photomatix results using just the RAW image came out reasonably well below: the colours in the building and the statue are stronger and give the picture more life, without looking over-saturated. The sky however looks washed out, almost as if it was part of a water painting. So Photomatixing a single exposure doesn’t seem to give great results, at least for this example – on to using our metered shot and ±1 exposed shots.

3. Photomatix Using RAW And Just ±1EV Exposures
Using the ±1EV exposures along with the RAW file has definitely improved the situation: there is a little more tonal range on the statue and across the building compared to the Photomaxifed RAW, and the sky is showing much improvement. I posted this photo over at The Photo Forum for some opinions. Now lets try ±2EV.

4. Photomatix Using RAW And Just ±2EV Exposures
The results of using ±2EV Exposures are similar to that of the ±1EV photo. We can tell though that the colours in the sky are slightly more contrasted / saturated. One improvement I think is the shadowing on the statue’s leg, which has been reduced a little due to the greater exposure range.

5. Photomatix Using RAW And Just ±3EV Exposures
OK now things are beginning to go downhill! Although the rest of the shot is holding up well, the sky has been washed out due to using too wide a range of exposures; remember the ±1EV or ±2EV have not been used here so we are missing all the information contained in those exposures – the gap between the metered shot at 0EV and exposures at ±3EV has grown too great. We need the information in these exposures to accurately capture the proper tones. Let see though what happens if we increase the exposure range even more!

6. Photomatix Using RAW And Just ±4EV Exposures
Well this is just a progression from the photo before – the sky is washed out even more. I’m surprised though that the rest of the image is more or less unchanged, I guess it has something to do with the original composition of colour and contrasts but I’m just guessing.

When taking multiple exposures for a HDR image and you only wish to take one on either side of you metered shot, there’s no real need to choose huge ±EV number: 1 or 2 seems to suffice: my S9600 offers auto braketing only up to ±1EV which I always thought was too narrow, until now! Go beyond 1 or 2EV and you risk saturating your photographs with cartoon like textures. If you like taking 5 or 7 shots for merging however, you can disregard this post!

Related Articles:
Tutorial To Create A High Dynamic Range Photo (HDR) From A Single RAW Image.
Creating Ultra Vibrant Tone-Mapped Surreal HDR Photos With Photomatix Pro