Canon CANOSCAN FB330 series Service Manual page 64

CHAPTER 2
When decreasing the resolution, the scanning unit moves at a faster speed to read less
lines.
6. Packing
Processed image data is stored in the buffer RAM before sent to the host computer. The
buffer RAM is divided into the writing block and reading block. While data is written into the
writing block, the data is read from the reading block. When fixed volume has been written,
the writing switches to the reading.
The scanner can output 8 bits each and 10 bits each of red, green, and blue images, while
the buffer RAM can be accessed only by 1 byte (8 bit) because of the hardware configuration.
Therefore, when outputting by 10 bits, the data is converted into 8 bits data to write in the
buffer RAM. This process is called a packing.
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COPYRIGHT © 1999 CANON INC. CANOSCAN FB330/FB630 SERIES REV.0 OCT. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
Sampling point
Moving direction
Scanning unit
Figure 2-26
Buffer RAM I (for writing)
Input
Buffer RAM II (for reading)
Fixed volume has been written
Buffer RAM I (for reading)
Input Buffer RAM II (for writing)
Figure 2-27
Output
Output