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Date Posted: 06:27:42 03/26/03 Wed
Author: Michel
Subject: Re: Jpeg compression? vs Tif?
In reply to: Dave Bracken 's message, "Jpeg compression? vs Tif?" on 16:30:56 03/25/03 Tue


Hi Dave,

I have had the same problem on a project I have worked on. The bottom line is that JPEG is not good for BW images. It is designed for photographic images. Converted a BW to 256 grayscale already increased the storage requires by 8, and the JPG does not do a good job at compressing it.

What I have done is use Tiff G4 for BW, and PNG for color 16/256, and JPG for true color. If these are to be displayed in a browser, PNG for BW will be better than JPG.

Best regards,

Michel

>Hello Michel,
>I have a scanning app that allows users to choose
>between 3 different formats when scanning. Tif, Jpeg,
>Bmp. When i scan the tif, i set the compression to
>tcGroup4. The file i am testing with ends up around 40
>k. Then i switch to jpeg, and scan the exact same file
>and it throws an exception because it does not seem to
>know the image is in greyscale, so i handle the
>exception and transform the image to greyscale. The
>resulting file size is about 400 k. Why is it doing
>this?
>I have verified that my scanner settings are set to
>256 gray before scanning. The dpi is set to 200.
>
>How do i let envision know the image is already
>greyscale, and then compress it down. I looked in your
>example app, but could not find any code pertaining to
>jpegs and how to compress them.
>Right now our scanners will only support black and
>white or greyscale images. But we soon will be
>scanning in color as well. The file size of the
>resulting jpegs are much to large for our purposes, so
>any help you can give in this matter would be greatly
>appreciated.
>
>Thanks in advance,
>Dave

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