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Why you should shoot RAW, Reason #479582 - HDR
25 March 2008
HDR, or High Dynamic Range for those of you who haven’t fiddled with it, is becoming all the rage in digital photography. Maybe it already has become…I don’t know, the semantics that alter due to my late entry into the art are kind of irrelevant. Anyhow, if you haven’t tried it, you should.
If you are totally new to this alien world, I highly, HIGHLY recommend that you skip past using the crappy tool built into Photoshop CS2/CS3 and the likes. Instead, go straight for a demo of the neat Photomatix by a company called HDRSoft. Original, I know.
The concept behind HDR is simple, but photography terms muck it up. Photogs will tell you that film and especially digital camera sensors are only sensitive to about 5 F-stops of light. An average scene encompassing both bright and dark areas will often go as high as 8 stops. That means you’re losing out on a full 3 stops of light range.
When you strip down the “stops”, it becomes a different matter. In the digital world, we represent color as bits. So an 8-bit image has 8 bits for each color, or 256 levels each for red, green and blue. If you add even one step up (to 10-bit), your options turn to 1024 levels per color per pixel. That means each pixel moves from having only 16 million possible colors to over 1 billion.
Cameras will tend to take the most careful note of colors (apply the highest bit-level) in the bright regions, where images get washed out - this way, you can recover blown highlights. HDR is the effort of taking one shot at several exposures, so that all parts of the scene are given that high-bit treatment. The dark shadows of each image are tossed, and the highlights of the next darkest picture are put in their place - thus giving a higher overall color fidelity. This means HDR is really a mosaic of different images, with the most balanced light being taken from each.
When you shoot in JPEG (no matter how high the quality), you are only ever shooting in 8-bit. Any dSLR on the market today has a minimum of 10-bit sensor, so that means you’re just “throwing out” 768 color levels. At minimum. Many better cameras have 12- and 14-bit sensors. The math there is even more frightening.
So, set your camera to RAW. Even if your screen will never show the full 10- to 14-bit color, it’ll be there when display technology improves and in the meantime, here’s some fun you can have with it:
I mentioned HDR is all about “mosaics”. When you shoot HDR, normally you take a bracketed exposure with at least three brackets per picture. But RAW data already captures more than your screen can show - and if you do too much HDR (There is such a thing), the picture starts to look quite unnatural. Even though your eyes normally “even out” the light more than a camera does, HDR is all about stripping shadows and highlights to give everything the ‘best’ lighting detail.
Rather than letting everything turn unnatural, try taking pictures that include lots of highlight and shadows and plugging just your single RAW file into Photomatix. Let it do the conversion to TIFF, rather than Lightroom or Aperture. You would be amazed how much more detail is actually in many shots - but a straight conversion loses it, and a full HDR rework takes it too far. By using just a single RAW, you’ll only alter the image by the data that’s already captured - meaning it won’t look horribly unnatural.
I stumbled on this by accident, as everywhere you read talks about HDR as a multi-exposure work-up. Sure, it can be done that way and there are reasons for doing it (it’s well worth experimenting), but I find that I like my pictures to err on the side of natural. Using a single RAW in Photomatix to apply an HDR tone-map really makes the lighting look more like what my eyes see, without over-doing it.
Topics: Post Processing, Technique |
March 26th, 2008 at 11:46 am
You REALLY need to post some sample shots to demonstrate this - ideally a straight jpg, single-RAW tone mapping, and a bracketed exposure tone mapping. Words are great, but you know what they say and it applies even more to photography articles.