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Hardware compress

Posted on 1998-11-03
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Last Modified: 2010-04-27
Hardware compress / decompress.
Could someone give me an elaborate explaination about this ?
I would like to know about the process of data transfer from scanner buffer to CPU buffer,what kind of data is that ?
Is it compressed data or raw data ? if compressed, what type of compression used ?

still related to the topic, TIFF group 4 compressed, does it refer to software compress or  hardware compress ?

thanks for the reply.
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Question by:asiasoft
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by:joopv
ID: 1128325
As far as i know, scanners never do data compression.  It is all done in software at the pc.

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by:khemicals
ID: 1128326
scanners just use the raw image... it is the software that does the compression... that is the reason that you can select so many compression formats for the image with the software
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joe_h earned 50 total points
ID: 1128327
As far as I know, there is no unified data format of data coming from the scanner to the computer. Any manufacturer can make up any format, with or without compression, that they will use to transfer scanned images to the computer. However, I would imagine that scanners do some kind of compression, especially if the scanner is connected to a (slow) parallel port - maybe a simple RLL, LZW or Huffman encoding (I don't think a scanner would have the computing power to perform JPEG compression fast enough).
It is the job of low-level scanner driver to present a meaningfull data to the calling application (or TWAIN driver). So, again, the scanner can send data in any format, as long as it is understood by its driver.
Now, the TWAIN driver (or, calling application) usually accepts data in JPEG compression. (It's not the only compression algorithm used, nor is the data required to be compressed.)

So, a short answer to what kind of data is coming over the scanner cable: It can be either - raw or compressed.

BTW, you can find more info on TWAIN and image scanning process in general at http://www.twain.org.

Now, TIFF group 4 (or 5?) refers to a data FORMAT - no matter if it has been compressed by software or hardware means. (You can have your image processing app save the image as compressed TIFF; or, you can have a hardware device that, when presented with raw data on one end, spits out TIFF out of the other end.)
However, in most cases TIFF compression is performed by software (image processing apps, etc); unlike MPEG compression, which is quite often performed by hardware.

HTH, Joe
P.S. Please post comments if you need any clarifications.

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by:asiasoft
ID: 1128328
Okay Joe, you have given me a comprehensive answer and the related links info pertaining to my question.

thanks a lot.
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Author Comment

by:asiasoft
ID: 1128329
Okay Joe, you have given me a comprehensive answer and the related links info pertaining to my question.

thanks a lot.
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