User guide

Chapter 21: Scaler MegaCore Function 21–3
Functional Description
January 2013 Altera Corporation Video and Image Processing Suite
User Guide
The sum is then weighted proportionally to these errors. Note that because the values
are measured from the top-left pixel, the weights for this pixel are one minus the error.
That is, in fixed-point precision: and
The sum is then:
Polyphase and Bicubic Algorithms
The polyphase and bicubic algorithms offer the best image quality, but use more
resources than the other modes of the scaler. They allow up scaling to be performed in
such a way as to preserve sharp edges, but without losing the smooth interpolation
effect on graduated areas.
For down scaling, a long polyphase filter can reduce aliasing effects.
The bicubic and polyphase algorithms use different mathematics to derive their filter
coefficients, but the implementation of the bicubic algorithm is just the polyphase
algorithm with four vertical and four horizontal taps. In the following discussion, all
comments relating to the polyphase algorithm are applicable to the bicubic algorithm
assuming 4×4 taps.
2
B
fh
err
i
–
2
B
fv
err
j
–
Oij  2
B
fv
B
fh
+
 Fin
i
in
j
2
B
fh
err
i
–2
B
fv
err
j
–=
+ Fin
i
1 in
j
+err
i
2
B
fv
err
j
–
+ Fin
i
in
j
 1+2
B
fh
err
i
–err
j

+ Fin
i
1 in
j
1++err
i
err
j
