Evaluating Sharpness


Today’s Question: In your “Evaluating Photos” video you discuss zoom for sharpness and you say that you should always zoom to a 1:1 ratio when doing so. Does the absolute need for sharpness have any relation to the eventual size of your print? That is, if I am going to print a 4×6, can I get away with the photo being not quite as sharp as when I am going to print larger sizes? At what size, if any, does sharpness become an absolute necessity?

Tim’s Quick Answer: I would say that the size of the print doesn’t change the need for sharpening, but rather changes the nature of the sharpening you should apply. For a larger print, for example, you will need stronger sharpening than would be necessary for a smaller print. But in almost all cases, sharpening is a necessary step in preparing a photo for print.

More Detail: When sharpening a photo that you are going to print, you’re not just compensating for the factors that reduce sharpness in the original capture, but also for the factors that reduce the apparent sharpness of the final print. Those factors contribute to a situation where it can be very difficult to evaluate sharpening settings for a photo without actually printing that photo.

The size of the final print certainly has a big impact on the sharpening settings, because it has an impact on the size of transitions for the detail and texture in your photo. There is also a secondary impact due to the viewing distance, since larger prints tend to be viewed from a greater distance (though that obviously is not always the case).

In addition, you need to consider the print process you are using. This includes a consideration of the type of printer being used, the type of ink being used, and the paper surface you are printing to. As just one example, in general you will need to apply stronger sharpening to a photo being printed to a matte paper surface than you would need to apply to the same photo being printed to a glossy paper surface. That is because with matte papers the inks will generally spread out more when they come in contact with the paper (this behavior is generally referred to as “dot gain”).

Even with a photo that was captured with perfect sharpness, you will still generally need to apply sharpening to the final image based on the output size and print conditions. Because of these factors, it is difficult to evaluate the sharpening settings based on a review of the photo on your computer’s display.

However, with a bit of experience you’ll start to understand the degree to which you need to “over-sharpen” the image based on the on-screen appearance in order to produce the best print for the output size and paper type you’re printing to, for example. With that experience, I do recommend evaluating the image at a 1:1 (100% zoom) setting in order to ensure the most accurate evaluation of the sharpening effect. But again, it does take some experience to be able to effectively evaluate those results based on the display of the image on your computer monitor.