Image Sharpness – by Glenn Woodell
We covered getting the image into the camera so now we’ll talk a little about what you do once you’ve acquired it.
Signal-to-Noise Ratio (SNR) is a techy sounding term for referring to what you want in your image as compared to what you don’t want. SNR is a ratio of the lightness values to the intrinsic noise values that your camera generates. You sometimes see noise as multicolored specs that show up when you lighten dark areas of an image. A camera with a higher SNR will tolerate more brightening than one with a lower SNR. And as handy as cropped sensor cameras are for giving you some free magnification, nothing in life is really free. Because the pixels in a cropped sensor camera are physically smaller than those of a full frame camera, they don’t collect as much light, so by definition, their SNR is always going to be less.
But all is not lost when using a cropped sensor camera, even if you underexpose. Hopefully by now you are shooting not in the default JPEG format, but in RAW, so that you can take advantage of the full dynamic range of the sensor of your camera. Although the learning curve for working with RAW images can be a daunting task for sure, the advantages are more than worth the effort. And if you’re not shooting RAW, you can still use much of the same software on your JPEG images. There is a lot of wonderful software available today that helps you take advantage of your camera and its features and especially can reduce the noise while adding some sharpening at the same time. Without getting into a technical discussion of JPEG images, just understand that the file format itself does add artifacts to your image that you have no control over.
Processing your images is where the magic of digital photography is leaps and bounds above that of traditional film and paper photography. Inexpensive and sometimes free software allows us to do things that were either too time consuming or near impossible in the darkrooms of yesterday.
Image blur and poor focus are hard to correct for in the processing. Both create a broadened or almost double edge. Contrast and sharpness however can be greatly enhanced, and should be since they are reduced intrinsically by the camera’s optics and electronics. And although the noise that is generated cannot be completely eliminated, it can be greatly reduced. Just realize that noise reduction tends to soften an image so sharpening will almost certainly need to be applied as well.
Especially with a lower SNR camera, you want to reduce your underexposing of your image. In the film days we were told to “shoot to the right” meaning we were to overexpose a little to make sure we didn’t generate excess film grain in the dark areas. That’s not so true today with the higher SNR cameras. I actually shoot to the left, making sure I don’t overexpose my highlights, knowing that the little noise that does show up can be mostly taken care of with my noise reduction software.
And finally, related to sharpness, contrast can be easily increased in a image as can general exposure and white balance, i.e., making sure your whites are white. This can be useful when you have a shaded subject that is illuminated solely by a blue sky. Since the illumination source is primarily blue, your subject will have a blueish cast to it which should be corrected in your processing.
While the software available to us today allows us to take full advantage of the capabilities of our digital cameras, we really need to make sure that we are starting with the best image possible. Maximizing sharpness and contrast while reducing image and camera blur can be done with some practice and the correct supporting equipment. You don’t have to buy the most expensive of everything but you do want to make sure that you are allowing your equipment to perform as best as it reasonably can by understanding its shortcomings and how to overcome them.
Featured image: Cy Curnin of The Fixx. Canon 6D with Canon 70-200mm/f2.8 lens
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