DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Don’t confuse PSF with
progressive segmented-frame
(PsF), described on page 62.
Figure 5.1 “Box” reconstruction
of a bitmapped graphic
image is shown.
Image structure 5
A naive approach to digital imaging treats the image as
a matrix of independent pixels, disregarding the spatial
distribution of light intensity across each pixel. You
might think that optimum image quality is obtained
when there is no overlap between the distributions of
neighboring pixels; many computer engineers hold this
view. However, continuous-tone images are best reproduced
if there is a certain degree of overlap; sharpness
is reduced slightly, but pixel structure is made less
visible and image quality is improved.
The distribution of intensity across a displayed pixel is
referred to as its point spread function (PSF). A onedimensional
slice through the center of a PSF is colloquially
called a spot profile. A display’s PSF influences
the nature of the images it reproduces. The effects of
a PSF can be analyzed using filter theory, which I will
discuss for one dimension in the chapter Filtering and
sampling, on page 141, and for two dimensions in
Image digitization and reconstruction, on page 187.
A pixel whose intensity distribution uniformly covers
a small square area of the screen has a point spread
function referred to as a “box.” PSFs used in continuous-tone
imaging systems usually peak at the center of
the pixel, fall off over a small distance, and overlap
neighboring pixels to some extent.
Image reconstruction
Figure 5.1 reproduces a portion of a bitmapped (bilevel)
graphic image, part of a computer’s desktop display.
Each sample is either black or white. The element with
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