Altera Video and Image Processing Suite - Manual (Page 224)

precision of each error variable is determined by the number of fraction bits chosen by the user, Bf
h
and
Bf
v
, respectively.
Their values can be calculated using the following equation:
The sum is then weighted proportionally to these errors.
Note: Because these 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 Algorithm
Polyphase and bicubic algorithms offer the best image quality, but use more resources than the other
modes of the Scaler II.
The polyphase and bicubic algorithms allow 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. 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.
UG-VIPSUITE
2015.05.04
Polyphase and Bicubic Algorithm 17-3
Scaler II IP Core Altera Corporation
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