With the advent of photography going to digital capture, we can now combine different exposures of the same image to more closely represent the range of tonality (dynamic range) that our eyes can actually see. Even though the tonality range of capture has increased with digital ( ~ 5 stops for slide film to ~6-8 stops, depending on who you talk to) this still falls short of the dynamic of the human eye at 10-14 stops of light (without adjusting iris size). Before digital photography, some of us use to do a type of HDR with film and scanning and Photoshop. You would then combine elements of photos to create an image that had a dynamic range greater than that of each individual image, but is was a pain in the backside to do.
Enough of the boring why’s. Let’s talk about the how to’s.
HDR imaging starts with good capture. The easiest way to capture a series of images is to set your camera to Auto Bracketing. If you are shooting Aperture preferred, then the camera adjusts the shutter speed to create the brackets. One of the problems with this (at least on Nikon cameras) is that the brackets can go no further apart than 1 stop. Sometime 3 images, one stop apart is enough. Sometimes you need more range than that and the only way to do it is with more images (five images gives you stops difference not 2 stops that you get with 3 images). You can always bracket manually or shoot completely on manual and get 3 images that are each 2 stops apart.
My procedure for HDR capture.
- Turn auto White Balance off (set to specific white balance setting and leave it).
- Turn auto focus off ( changing focus can really mess up blending an HDR).
- Decide how much of a range of exposure you need to capture nice details in the shadows and detail in the highlight areas. One way is to capture images and look at your histogram. See what exposure it takes to get your histogram completely not touching the right side of the range (this means all your highlights have detail). Then see what exposure it takes to get your histogram to not touch the left side of the range (all your shadow images will have detail). See what the difference is between preserving highlight detail and preserving shadow detail. This is how many stops you will need to capture to get a good HDR.. if it is 2 stops (going from 1/125s to 1/30s, say), then 3 images, one stop apart will do. If it is 4 stops ( going from 1/125s to 1/8s) then you need either 5 images, one stop apart or 3 images that are each 2 stops apart..
- Reference for starting and stopping a series. I use a picture of my hand to signify a series that belong to each other. I also use this when shooting panorama elements.
- Remember to turn Auto Bracketing OFF.. It’s really frustrating to have some great action occurring in front of you then realize that the perfect frame is 2 stops over exposed because of bracketing (been there, down that, have the t shirt).
Tomorrow show a comparison of 1 set of images with 4 different HDR processing software.. Stay tuned.