Message-Id: <mailto:199409150725.CAA07394@library.wustl.edu> Date: Wed, 14 Sep 1994 15:28:02 -0400 From: Pamela Mason <mailto:pmason@NALUSDA.GOV> Subject: Re: 8-bit vs. 24-bit color To: Multiple recipients of list IMAGELIB <mailto:IMAGELIB@ARIZVM1.BITNET>
On 14 Sep 1994, ERNEST WILLSON-POWER DEPT. wrote:> Pamela,
>
> I believe that Matthew is asking about black and white
> photographs, not documents. I would also like to know what is the
> best format for electronic storage and retrieval of b/w photos.
> Can you help us?
>
> Thanks,
>
> Ernie Willson
>
Black and while photos, or continuous tone images, can be saved as bitonal images; these can be "dithered" to create the same continuous tone effect, but then the text is not clear if there's a mix of text and illustration. When scanning text pages which have continuous tone illustrations, I believe it is often sufficient to scan as a bitonal image. If that is not acceptable, then the page would have to be scanned as grayscale. In the National Agricultural Text Digitizing Project, lead by my colleague, Judi Zidar they're scanning text as bitonal images, saving them as TIFF (tagged image file format) files, compressed using the CCITT Group 4 (like fax) compression algorithm. If one were just handling photographs, and not the mix of text and images they're doing, I'd guess that saving the image as grayscale would be more appropriate. In that case 8-bit grayscale would be the minimum for most use, and 24-bit would be desirable. Here, I'm on less familiar ground, since I don't work with these. I know the usual caveat is that one can't distinguish more than 256 shades of gray, so 8-bit grayscale might in fact be all right. Comments invited. I'm copying this reply to my colleague who works with these types of images, so she can also comment.Pamela *ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ*ÿ* | Pamela Mason, Project Manager | National Agricultural Library |
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