Friday, April 14, 2017

Extending Dynamic Range

Contrary to want a lot of people believe Digital Cameras, even the best ones, are not capable of capture the full extent of light from the darkest blacks to the purest white. They struggle to get close to the capabilities of traditional film and they are certainly no where near as capable as the human eye. This range of illumination is usually referred to as Dynamic Range. This limited range coupled with an automatic light meter that is trying to get an average exposure (ie matching a mid tone grey overall) is the reason a lot of images turn out boring, washed out and flat looking even though you remember much stronger light (and often colour)._IGP6498 Untouched RAW Image as Rendered by Lightroom

Here are a couple of techniques that can help you get a wider apparent Dynamic Range in your final photo.IMAG0167 - AutoHDR using HTC UPlay CameraThe first is the use a camera app on your phone that will take an “AutoHDR” (this usually means it will take 3 exposure and combine then using software with the app, a few will do pseudo HDR a bit like the next approach.) This is the simplest approach and results can be surprisingly good.

_IGP6497A second approach is to take a RAW image (this is in .PEF format) and use software (I’m using lightroom Develop basic panel only.) I’m following what I once called SDR+ (standard dynamic range plus) and I even wrote a couple of presets to do it. The basic idea is I bring up detail in the shadows (usually moving the shadow slider to the right, sometimes I also change the blacks using the approach often called “finding the black point”, while on the black slide hold down the <alt> and the scree turn black,image the adjust the slider till a few whit areas (these are the areas that will be rendered pure black) show up. You can do a similar operation with the white slider. The objective is to get the illumination histogram to be as evenly spread across the range as possible. This doesn’t take all that long  and I prefer to do it manually to even my own preset, but it requires specialist software, some skills in the oftware and a camera that can take RAW files. Many RAW purist will explain this is why you should always take RAW images.

_IGP6496_HDRThe third approach is classic HDR (High Dynamic Range) and here I am using three bracketed +/-1 EV exposures. Then the Nik HDR Efex Pro 2 software and the balanced preset to create a new 16-bit colour .Tiff file. There are many variation of the HDR technique and software, but it normally involves two steps. First collecting and preserving the full range of illumination values from the three or more exposures. Then a second step of “tone mapping” these into the available dynamic range of your image (and this is also related to how you might reproduce the image, eg print or screen). The downside is these steps and any image prep take extra time and a lot of folk get carried away with the slider options in the “tone mapping” step, thereby producing the sickly vivid and disturbingly surreal images that have given HDR  a bad name. I personally think this method has give me a final photo much closer to the late afternoon light I was photographing in. I have to admit I do take a lot of HDR images, particularly in contrasty light or where I know I need to preserve the Highest Dynamic Range possible.

So if you are disappointed with flat washed out images you might like to investigate at least one of these approaches.

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