The confusion is understandable but rarely serious because the end results are visually similar. But when sharpening is analyzed in the frequency domain the differences become significant. Here is a great example from a PBS broadcast.
Alternate Youtube page. The next generation of slide or print was made from a sandwich of the original transparency and the fuzzy mask. This mask served two purposes. Unsharp masking was an exacting and tedious procedure which required precise processing and registration. You can observe the effects of USM using the Matlab imsharpen routine in the Imatest Image Processing module, where you can adjust the blur radius, amount, and threshold settings.
Thanks to the central limit theorem , blur can be approximated by the Gaussian function Bell curve. Actual sharpening is a two dimensional operation. Nasse of Carl Zeiss. Excellent, thorough introduction. Here is an interesting list of Zeiss technical articles.
Moderately technical. SQF subjective quality factor is a measure of perceived print sharpness that incorporates the contrast sensitivity function CSF of the human eye.
It will be added to Imatest Master in late October Optikos makes instruments for measuring lens MTF. Documentation — Current v It has been deprecated] The sharpening process Sharpening on a line and edge A simple sharpening algorithm subtracts a fraction of neighboring pixels from each pixel, as illustrated on the right.
Oversharpening and Undersharpening Oversharpening or undersharpening is the degree to which an image is sharpened relative to the standard sharpening value. They are intended to indicate whether oversharpening the image has enough sharpening to cause an overshoot the eye tolerates significant overshoot , or undersharpening low enough sharpening so that image appearance would benefit from additional sharpening.
Examples: under and oversharpened images Undersharpened image. Undersharpened image. Oversharpened image. The image above is for the 5 megapixel Canon G5, which strongly oversharpens the image— typical for a compact digital camera.
MTF50P is not shown. It is displayed when Standardized sharpening is turned off; it can also be selected as a Secondary readout. It makes the details you already have appear to stand out a little more. Can a sharpening program make this image less blurry? Can it give us back some of the detail lost on the child's face? And this is the result. The parts of the image that were out of focus are still blurry.
After the sharpening, the background that's in focus looks better, but our main subject is still very blurry. When you think about it, the sharpening program did exactly what we would normally expect it to do. It brightened the bright pixels and darkened the dark pixels. The areas that were already in focus have a little more contrast, but the rest of the image remains mostly unaffected.
Sharpening programs are not intelligent. They only do one thing. They brighten the bright parts and darken the dark parts. No more. No less. How do you use sharpening and post-production in your digital photography? Let me know by leaving a message below.
Thank you for the info. I have been using the "sharpen" tool on most of my pics but really did not understand how it worked. I found this article by searching "What is "Photo Sharpening"? I always start the sharping process only on my "Keepers", sometimes the picture just doesn't need it and I back off.
I find sharpening an art along with adjusting exposure and color. I enjoy your tips and look forward to them daily. Thanks, Dave. I do sharpen my images quite often, but I've always felt it was somehow "cheating" and that I hadn't done a good job taking the picture in the first place, although I'm very careful not to move the camera, and to use myself and something near me as a "tripod" if I can.
This article has eased my conscience about sharpening my pictures. Thanks again. Do I sharpen ALL my images? Some images need sharpening and others not at all. More or less knew about sharpening. Your explanation is very clear. Now I know about unsharp mask. However, there are more and different sharpening tools.
Get CNET's comprehensive coverage of home entertainment tech delivered to your inbox. The easiest way to check is to switch your TV to the Movie or Cinema picture preset, and see where the sharpness control is in that mode. Whatever that number is, it's a good place to start.
Want to fine-tune it? While watching a variety of content, especially 4K if you have a 4K TV, turn the control down from that starting point and see what happens. Does the fine detail disappear? If so, that's too low. Ideally, you'll be able to find the spot that offers the most actual detail and the least additional noise.
Don't be surprised if that number is 0. Some TVs actively soften the image when you turn the sharpness control to zero or even below 50 in some cases. This might be done to offer a way to decrease the noise in lower-quality sources, but I'd be shocked if it's ever used for that purpose. Just something to keep in mind. If the image suddenly looks blurry , that's definitely too low. There's a sweet spot with any TV, it's just a matter of finding it.
It's possible, though rare, that you have a TV with permanent edge enhancement. Even turning the sharpness control to zero and going through every setting and picture preset in your TV, you still may see edge enhancement or other processing. This was more common with older TV sets, though. These days it's fairly rare. Many TVs and some high-end projectors have processing features separate from the sharpness control. These are usually deeper in the settings menus, or in separate "advanced" sections.
Some of these can enhance the apparent detail without adding undue amounts of edge enhancement. Others, of course, do more harm than good. Part of this is due to the increase in overall processing power available in mid- and high-end TVs. For instance, Samsung, LG, and Sony have discussed using AI for their upconversion , which is how you get a decent-looking lower-resolution image on a high-resolution television. There's no blanket advice here. Sit close, and see if it's adding noise, edge enhancement, or if it's making the image appear sharper.
Purists will likely want to keep these features off, especially with high-quality content like from a 4K Blu-ray, but with some content it might help.
Occasionally, the edge enhancement is in the source.
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