Message-Id: <mailto:199504062313.SAA28356@library.wustl.edu> Date: Thu, 6 Apr 1995 10:28:32 -0500 From: Sandeep Somaiya <mailto:sandeep@NEXT2.VTLS.COM> Subject: Re: Imaging Questions To: Multiple recipients of list IMAGELIB
John Pillans <mailto:jpillans@SUN.CIS.SMU.EDU> wrote: >>Is there a source to find out which image type (GIF,JPEG etc.) is
>>best for different types of material to scanned.
Some references on graphics file formats: -Encyclopedia of Graphics File Formats;Murray and vanRyper, O'Reilly & Associates -Graphics File Formats; Kay and Levine, Windcrest Books/McGraw-Hill -Bit-mapped graphics; Steve Rimmer, Windcrest/McGraw-Hill
Considering the three most popular formats - TIFF vs.JPEG vs.GIF. [There are several other formats (BMP, JFIF, PCX etc.) and compression types]. - JPEG compression is best storing full-color [24 bits/pixel]or grey-scale [8-bit] images of realistic scenes such as scanned photographs. It will also give good results with semi-realistic images such as fantasy drawings etc. Is lossy. - GIF is a data stream-oriented file format used to define the transmission protocol of LZW-encoded bitmap data. GIF images may be up to eight bits (256 colors) in depth and are always compressed. Despite the fact that GIF supports only 8-bits worth of colors GIF still remains a popular choice for storing lower resolution image data. GIF compression does significantly better on images with only a few distinct colors, such as line drawings and simple cartoons. Images that have large areas of the same color work well with GIF too. And similarly images with few distinct colors. Also with images with sharp edges such as borders, overlaid text etc. GIF for images with 8-bit-per-pixel data. Is Lossless.256 or fewer color;cannot be used on images with full-color-24bit. - Computer generated images usually fall between photographs and cartoons in terms of complexity and for them if the image is more like a photograph JPEG might help whereas for images that have are more like cartoons GIF might be better. - TIFF format is used for most kind of images but the compression scheme used varies depending on data: a.TIFF with CCITT Group III or IV compression for plain black-and-white bi-level images/documents. [recent development for this type JFIF] b.TIFF with JPEG compression same arguments as with JPEG above apply c.TIFF with LZW same arguments as with JPEG above apply except in this case but it would be lossless. But the format and compression you use will depend on several factors and not just the types of material such as time/space tradeoff, image size, lossy, need for networked access, need for hardcopy reproduction, aim to preserve, aim to preserve and increase access, only increase access, available hardware and software for digitizing and end-user, need to OCR, whether image is scanned at 1bit, 2bit, 4bit, 8bit, 12bit, 24bit, 32bit etc., storage space available, budget etc. etc. In addition to TIFF, JPEG and GIF considered above in some cases Kodak PhotoCD option might be attractive too. And similarly some other formats and compression schemes.
Hope this information helps.
Sandeep Somaiya VTLS Inc. "Look, Learn, Listen ... Libraries change Lives" [information from USENET feeds and threads. Standard disclaimer applies.]