
92 Image Processing for Cinema
color correction methods that also enhance the contrast without introducing
artifacts such as halos or spurious colors.
Basic edge enhancement is linear: an edge map E is computed from the
image I, scaled and added back to I to obtain the sharpened image I
0
[68]:
I
0
= I + kE. (3.30)
A common way to compute the edge map is through an “unsharp mask”:
the image I is blurred by convolution with a Gaussian g, then subtracted from
the original I to obtain E [68]:
E = I − g ∗ I. (3.31)
FIGURE 3.26: Linear edge enhancement (unsharp masking). Top left: edge.
Top right: aftter Gaussian blur. Bottom left: edge map. Bottom right: sharp- ...