Sharpening: Unsharp Mask vs. Contrast Adaptive Sharpening

To sharpen a video in vPrism, click Adjust in the Tool Panel and select Sharpening. Choose a method from the dropdown: Unsharp Mask or CAS.

Unsharp Mask is a technique that dates back to analog film processing. The algorithm takes the original frame, produces a blurred version of it, and then calculates the difference between the two. That difference represents the fine detail present in the original that the blurred version lacks. A scaled version of that difference is then added back to the original frame, increasing the perceived sharpness of edges and detail.

Two sliders control the result. Size defines what qualifies as fine detail, larger values target broader edges, smaller values target finer detail. Strength controls how much of that detail is added back; higher values produce a more pronounced effect.

CAS, or Contrast Adaptive Sharpening, takes a different approach.

Rather than applying a uniform sharpening pass across the entire frame, CAS reads the local contrast around each pixel and adjusts sharpening accordingly, dialing it down where contrast is already high and increasing it where contrast is low.

The result is a sharper image that tends to look less processed than traditional sharpening methods. A single Strength slider controls the overall intensity.

Click Apply to commit the sharpening, or Reset to revert.

Both methods improve the perceptibility of existing detail: Unsharp Mask with more direct control over what is sharpened and by how much, CAS with a more adaptive, natural-looking result.