NEC uPD72257, Preliminary User'S Manual

Page: 160 / 343

6.4.2 Scaling
The captured image content is passed on to a scaler unit, that features
independent scaling of the data in x- and y-direction. The geometry of the scaler
output image is defined by the registers
• VInSCALEDWIDTH.SCWIDTH[10:0] defines the number of pixels per
scaled line and must be a multiple of four pixels. Thus
VInSCALEDWIDTH.SCWIDTH[1:0] is always 00
B
.
• VInSCALEDHEIGHT.SCHEIGHT[9:0] defines the number of lines per
field.
When the scaled width/height values of VInSCALEDWIDTH and
VInSCALEDHEIGHT are reached no more pixels are passed on. Thus
VInSCALEDWIDTH and VInSCALEDHEIGHT effect a cropping of the incoming
image at the right and bottom edge.
The diagram below outlines the structure of the scaler unit.
At first the captured pixel data is supplied to the y-scaler. Upon start of a new
frame the y-scaler is reset and the xin- and y-coordinates are set to address the
first pixel of the first line.
Depending on the y-scaling factor a decision is taken whether the current line
produces an output.
If not, only the luminance values Y for each pixel of that line are calculated, which
contribute later to the calculation of the output lines.
If a line is to generate an output, the x-scaler is initialized. For each pixel of the
output line a y-scaler output Pyout[xin] is calculated, regarding the luminance
values of the current line as well as those of previous lines.
Pyout[xin] is supplied to the x-scaler.
Depending on the x-scaling factor a decision is taken whether the current pixel
Pyout[xin] produces an output Pxout[xout].
If not, only an intermediate output pixel is calculated, which contribute later to the
final output pixel Pxout[xout].
If a pixel is to be output, the final pixel is calculated and output.
Chapter 6 Video Input (Ravin-M only)
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Preliminary User's Manual S19203EE1V3UM00