In my last installment I talked about potentially Red-lining your ISO by setting a desired shutter speed and letting your camera's auto-ISO feature keep up by adjusting the sensitivity. As advertisers are fond of saying, results may vary- make sure to play around with ISO on your camera to see how far you can push your sensor and still have acceptable results.
The main issue with high-ISO settings is the image noise that can be introduced. This is sort of like of the digital equivalent of film grain for those of us who can remember shooting slides or print film. Basically, with faster ISO settings more random electronic noise will be introduced to the image, degrading its quality. In general, newer cameras with later-generation sensors handle high-ISO settings with better noise control. Larger sensors (like those found on full-sized DSLR bodies) are also generally less "noisy" than smaller sensors found on compact cameras. Check your shooting menu- many cameras have a high-ISO noise reduction setting to help get cleaner images when you are red-lining your ISO. Noise can be very hard to see on busy, focused backgrounds like branches, leaves, and grass, but is most noticeable in shadows and dark, out-of focus backgrounds.
As a general rule I'd rather have sharp but noisy images instead of soft, "clean" snaps as noise can be dealt with easier than soft focus. Here's an example of a really high-ISO shot is used in my last post, a Hermit Thrush image shot at ISO 6400. This is what it looks like out of the camera (opened in Adobe Photoshop Elements for editing):
Note that the picture looks a little washed out. Composition isn't great, either, but to focus on the bird and get the metering right I centered on the adult bird. So let's start with a more pleasing crop:
By next going to 100% view, we can evaluate the picture. It is pretty sharp (noting the facial feathering detail, for example) but also quite noisy (click on the image to enlarge and note the green background.) Realistically, this wouldn't make a great cover shot for the next Birding Magazine, but all hope is not lost…
The first thing I suggest is running a noise reduction filter. I use NoiseWare, which runs as a plug-in from the filters menu in Photoshop or Photoshop Elements. There are certainly other options, either as built-in features in photo editing software or as aftermarket products. Most of the time with NoiseWare I find the default values work well (plus I'm lazy and would rather look at birds than at a computer), but other presets are available along with user-customized settings. Check out how much the image cleans up with a NoiseWare pass:
After processing for noise, I'll re-size the image. Since this is for the web and/or email, I'll make it 14" wide @ 72 dpi.
Finally, I'll slightly adjust the levels so the bird looks like what I remember seeing:
And Shazzam- a slick pic of a neat bird encounter, much improved by about 1 minute of post-processing:
Here's one more case study of a high-ISO photo, this time of a Broad-tailed Hummingbird I shot in my back yard last August. I really like the dramatic dark background, but that kind of backdrop is especially prone to showing sensor noise. This image was shot at ISO 1800, with exposure compensation at -2/3 to avoid blowing out highlights on the sunlit bird. Here's what it looks like out of the gate:
Rotated and enlarged to 100%, the dark background looks pretty noisy:
So I'll run it through NoiseWare to get this:
A quick crop, re-size, level adjustment, & wee bit of sharpening leaves a pleasing image for the web or email:
Any other noise reduction tips? If you have a product to recommend or technique to try please leave a comment!
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