IPSR-VIDEO Altera, IPSR-VIDEO Datasheet - Page 135

• Manufacturer Part Number: IPSR-VIDEO
• Description: RENEWAL Of IPS-VIDEO
• Manufacturer: Altera
• Series: IP Suitesr

Specifications of IPSR-VIDEO

• Software Application: IP CORE, SUITES
• Supported Families: Arria GX, Cyclone II, HardCopy II, Stratix II
• Features: Common Avalon Streaming (Avalon-St) Interface And Avalon-St Video Protocol
• Core Architecture: FPGA
• Core Sub-architecture: Arria, Cyclone, Stratix
• Rohs Compliant: NA
• Lead Free Status / RoHS Status: na

Chapter 5: Functional Descriptions
Scaler
January 2011 Altera Corporation
Polyphase and Bicubic Algorithms
Algorithmic Description
This section describes how the algorithmic operations of the bilinear scaler can be
modeled using a frame-based method. This does not reflect the implementation, but
allows the calculations to be presented concisely. To find a value for an output pixel
located at (i, j), we first calculate the corresponding location on the input:
The integer solutions,( in
left corner of the four input pixels to be summed. The differences between in
( in
real-valued position that we want to read from. Call these errors err
precision of each error variable is determined by the number of fraction bits chosen by
the user, B
Their values can be calculated as:
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:
The sum is then:
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.
O i j
in
in
where % is the modulus operator and max(a, b) is a function that returns the
maximum of two values.
i
û, in
i
j
= (i × w
= (j × h
2
j
û) are a measure of the error in how far the top-left input pixel is from the
fh
B
fv
and B
+ F in
+
in
in
B
)/h
)/w
fh
=
out
fv
i
out
, respectively.
F in
in
j
i
+
1
in
i
û, in
j
err
err
2
B
j
2
û) to these equations provide the location of the top-
i
j
fh
2
B
=
=
B
–
fh
fh
–
err
------------------------------------------------------------ -
--------------------------------------------------------- -
–
err
i
j
err
i
max w
max h
i
w
i
h
err
in
in
and
2
%w
%h
+ F in
j
in
in
B
fv
2
out
out
B
–
w
h
fv
out
err
out
i
–
+
err
j
+ F in
2
1 in
Video and Image Processing Suite User Guide
2
B
B
j
fv
fh
j
i
+
+
1
1 in
err
j
i
i
and err
err
err
i
j
2
j
. The
B
i
, in
fv
–
j
err
and
5–55
j