Help file has incorrect description of unsharp filter
Submitted by Windsurfer
Link to original bug (#790504)
Description
The last but one sentence below should read:
Let us add the difference between blurredness intensity and the intensity of the image to the intensity of the image.
3.9.4. How does an unsharp mask work?
Using an unsharp mask to sharpen an image can seem rather weird. Here is the explanation:
Think of an image with a contrast in some place. The intensity curve of the pixels on a line going through this contrast will show an abrupt increase of intensity: like a stair if contrast is perfectly sharp (blue), like an S if there is some blur (yellow).
Now, we have an image with some blur we want to sharpen (black curve). We apply some more blur: the intensity variation will be more gradual (green curve).
Let us subtract the blurredness intensity from the intensity of the image. We get the red curve, which is more abrupt: contrast and sharpness are increased. QED.
Version: 2.8