What does unsharp mask mean

what does unsharp mask mean

Should make Unsharp Mask on when scanning

Unsharp masking (USM) is an image sharpening technique, often available in digital image processing software. Its name derives from the fact that the technique uses a blurred, or "unsharp", negative image to create a mask of the original image. (usually only on angled or jagged edges). Unsharp Mask is the opposite, it involves making the pixels on the light side of the edge even lighter, and making the pixels on the dark side of the edge even darker, as shown, to increase edge contrast. This then shows the edge better, therefore we perceive the edge to be sharper.

An "unsharp mask" is actually used to sharpen an image, contrary to what its name might lead you to believe. Sharpening can help you how to fake gps ingress texture and detail, and is critical when post-processing most digital images. Unsharp masks are probably the most common type of sharpening, and can be performed with nearly any image editing software such as Photoshop. An unsharp mask cannot create additional detail, but it can greatly enhance the appearance of detail by increasing small-scale acutance.

The sharpening process works by utilizing a slightly blurred version of the original image. This is then subtracted away from the original to detect the presence of edges, creating the unsharp mask effectively a high-pass filter. Contrast is then selectively increased along these edges using this mask — leaving behind a sharper final image. Note: Step 2 combines the three images using a "mask overlay," which is when image information from the layer above the unsharp mask passes through and replaces the layer below in a way which is proportional to the brightness in that region of the mask.

The upper image does not contribute to the final for regions where the mask is black, while it completely replaces the layer below in regions where the unsharp mask is white. If the resolution in the above image is not increasing, then why is the final text so much sharper?

We can better see how it works if we magnify and examine the edge of one of these letters as follows:. Note how it does not transform the edges of the letter into an ideal "step," but instead exaggerates the light and dark edges of the transition. An unsharp mask improves sharpness by increasing acutance, although resolution remains the same see sharpness: resolution and acutance.

Note: Unsharp masks are not new to photography. They were traditionally performed with film by utilizing a softer, slightly out of focus image which would act as the unsharp mask. The positive of the unsharp mask was then sandwiched with the negative of the original image and made into a print. This was used more to enhance local contrast than small-scale detail. It turns out that an unsharp mask is actually utilizing a trick performed by our own human visual system. The human eye sees what are called "Mach bands" at the edges of sharp transitions, named after their discovery by physicist Ernst Mach in the 's.

These enhance our ability to discern detail at an edge. Move your mouse on and off of the following image to see the mach band effect:. Note how the brightness within each step of the gradient does not appear constant. On the right side of each step you what do baclofen pills look like notice it is lighter, whereas on the left it is darker — very similar to the behavior of an unsharp mask.

Move your mouse over the plot below to see what is happening:. Fortunately, sharpening with an unsharp mask in Photoshop and other image editing programs is quick and easy.

Using the unsharp mask requires understanding its three settings: "Amount," "Radius," and "Threshold. Amount is usually listed as a percentage, and controls the magnitude of each overshoot.

This can also be thought of as how much contrast is added at the edges. Radius controls the amount to blur the original for creating the mask, shown by "blurred copy" in the TEXT illustration above. This affects the size of the edges you wish to enhance, so a smaller radius enhances smaller-scale detail. Threshold sets the minimum brightness change that will be sharpened. This is equivalent to clipping off the darkest non-black pixel levels in the unsharp mask.

The threshold setting can be used to sharpen pronounced edges, while leaving subtle edges untouched. This is especially useful to avoid amplifying noise, or to sharpen an eye lash without also roughening skin texture. Unsharp masks are wonderful at sharpening images, however too much sharpening can also introduce "halo artifacts. Halos artifacts become a problem when the light and dark over and undershoots become so large that they are clearly visible at the intended viewing distance.

Remedies : The appearance of halos can be greatly reduced by using a smaller radius value for the unsharp mask. Alternatively, one could employ one of the more advanced sharpening techniques coming soon. Another complication of using an unsharp mask is that it can introduce subtle color shifts.

Normal unsharp masks increase the over and how to draw canada hetalia of the RGB pixel values similarly, as opposed to only increasing the over and undershoots of luminance. In situations where very fine color texture exists, this can selectively increase some colors while decreasing others.

Consider the following example:. When red is subtracted away from the neutral gray background at the edges middle imagethis produces cyan color shifts where the overshoot occurs see subtractive color mixing. If the unsharp mask were only performed on the luminance channel right imagethen the overshoot is light red and the undershoot barely visible becomes dark red — avoiding the color shift. Remedies : Color shifts can be avoided entirely by performing the unsharp mask within the "lightness" channel in LAB mode.

A better technique, which avoids converting between color spaces and minimizes posterizationis to:. Move your mouse over unsharp mask and sharpened to see how the sharpened image compares with the softer original image. The difference can often be quite striking. Want to learn more?

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Alternating with a smooth gradient enhances the mach band effect. Soft Original. Luminance Sharpening. Original Unsharp Mask Sharpened Unsharp mask brightened slightly to increase visibility. Follow us via Email Facebook Twitter. Unsharp Mask.

Sharpening - Unsharp Mask

Unsharp Mask. You can select or deselect the Unsharp Mask setting. Selecting this check box improves image sharpness. Note: If Pixel Depth is set to Black & Whiteor Color Smoothing is set to Onin the Image Type dialog box, this check box appears dimmed and cannot be selected. Unsharp mask off. Unsharp mask on. Jun 09,  · Unsharp Mask Set the [Unsharp Mask] function to ON to sharpen outlines in an image. This function is effective when an image's focus is fuzzy. It enhances the crispness of the overall image. Of course another possibility is that the term "Unsharp Mask" means something completely different in DPP4 than it does in other image editing software. If so, is it possible to find a documented explanation of what the tools is doing? In that, a more elaborate explanation than what is .

Unsharp masking USM is an image sharpening technique, often available in digital image processing software. Its name derives from the fact that the technique uses a blurred, or "unsharp", negative image to create a mask of the original image. The unsharp mask is then combined with the original positive image, creating an image that is less blurry than the original.

The resulting image, although clearer, may be a less accurate representation of the image's subject. In the context of signal processing, an unsharp mask is generally a linear or nonlinear filter that amplifies the high-frequency components of a signal. We're doing our best to make sure our content is useful, accurate and safe.

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