Canon MultiPASS C530 Service Manual

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2-51MultiPASS C530/C560 Chapter 2: Technical ReferenceThe characteristics of Progressive Bi-level Image Compression are explained below as areference. First of all, after the original image has been read in at high resolution, it isconverted to low resolution, and this low resolution image data proceeds to be encoded(compressed). On the receiving end, the overall original image can be quickly recognizedby the steps in which this low resolution image compression data is received.Next, to improve the quality of the low resolution image already sent, only informationneeded to improve the resolution is forwarded. The previous low resolution image isdecoded on the receiving side with this information, and following this, the highresolution image is displayed on top of the previous low resolution image.It is easy to quickly recognize the original image in the process of displaying the imagefrom low resolution to high resolution in order by using this method, with a CRT displayfor example. Also, according to the situation, it is possible to interrupt the image transferat the point where the original image is recognized to some degree by the receiving side.This method requires a page buffer memory for the low resolution image because the lowresolution images are used for the purpose of high resolution image encoding.8.2.2 Single progression sequential bi-level image compression methodThe Single Progression Sequential Bi-level Image Compression Method used in this fax is explainedbelow.The Progressive Bi-level Image Compression Method uses multiple resolution layers on a single page(multi-level layers, low resolution layers~high resolution layers) to perform encoding/decoding. In theSingle Progression Sequential Bi-level Image Compression Method, encoding is done in units ofhorizontal bands (a number of lines) called stripes, and is performed from left to right, top to bottom (thiscondition is called sequential), and in one resolution layer (single layer).In this method, the encoding is done in stripe units, so it is completed with a buffermemory much smaller than a page buffer memory.The methods by which encoding takes place and by which image data is constructed after encoding areexplained below.NOTENOTE