Message-Id: <mailto:199503110318.VAA23889@library.wustl.edu> Date: Fri, 10 Mar 1995 19:00:42 -0800 From: Robert MacKimmie <mailto:rm@CALIFHISTSOC.ORG> Subject: Re: JPEG and image size - (Comparative Data Results...) To: Multiple recipients of list IMAGELIB
Details of LZW/JPEG compression comparison (the first number is meg.kilobytes, then image info):24-bit color: megs 10.500 24-bit, 300dpi, 10 x 4" no compression 5.800 24-bit, 300dpi, 10 x 4" LZW compression 1.490 24-bit, 300dpi, 10 x 4" JPEG 002:1 compr 0.882 24-bit, 300dpi, 10 x 4" JPEG 005:1 compr 0.604 24-bit, 300dpi, 10 x 4" JPEG 010:1 compr 0.378 24-bit, 300dpi, 10 x 4" JPEG 020:1 compr 0.257 24-bit, 300dpi, 10 x 4" JPEG 035:1 compr 0.204 24-bit, 300dpi, 10 x 4" JPEG 050:1 compr 0.167 24-bit, 300dpi, 10 x 4" JPEG 075:1 compr 0.142 24-bit, 300dpi, 10 x 4" JPEG 100:1 compr 0.119 24-bit, 300dpi, 10 x 4" JPEG 150:1 compr 0.107 24-bit, 300dpi, 10 x 4" JPEG 200:1 compr 0.099 24-bit, 300dpi, 10 x 4" JPEG 250:1 compr 0.099 24-bit, 300dpi, 10 x 4" JPEG 254:1 compr
24-bit color, 72 dpi: megs 0.606 24-bit, 300dpi, 10 x 4" no compression 0.374 24-bit, 300dpi, 10 x 4" LZW compression 0.130 24-bit, 300dpi, 10 x 4" JPEG 002:1 compr 0.059 24-bit, 300dpi, 10 x 4" JPEG 010:1 compr 0.038 24-bit, 300dpi, 10 x 4" JPEG 020:1 compr 0.021 24-bit, 300dpi, 10 x 4" JPEG 050:1 compr 0.014 24-bit, 300dpi, 10 x 4" JPEG 100:1 compr 0.011 24-bit, 300dpi, 10 x 4" JPEG 150:1 compr 0.010 24-bit, 300dpi, 10 x 4" JPEG 200:1 compr 0.009 24-bit, 300dpi, 10 x 4" JPEG 250:1 compr
8-bit grayscale of same image: megs 3.510 08-bit, 300dpi, 10 x 4" no compression 2.000 08-bit, 300dpi, 10 x 4" LZW compression 1.160 08-bit, 300dpi, 10 x 4" JPEG 002:1 compr 0.497 08-bit, 300dpi, 10 x 4" JPEG 010:1 compr 0.308 08-bit, 300dpi, 10 x 4" JPEG 020:1 compr 0.161 08-bit, 300dpi, 10 x 4" JPEG 050:1 compr 0.111 08-bit, 300dpi, 10 x 4" JPEG 100:1 compr 0.096 08-bit, 300dpi, 10 x 4" JPEG 150:1 compr 0.086 08-bit, 300dpi, 10 x 4" JPEG 200:1 compr 0.079 08-bit, 300dpi, 10 x 4" JPEG 250:1 compr
This is a scan which measures 10" high by 4" wide. The subject matter in the digital image is a
Stanford University commemorative ribbon dated 1876. The ribbon has gold colored metal and trimmings with deep purple fabric as the body of the ribbon and a medium gray background. The similar colors of the ribbon and background allow both the LZW and JPEG to work much more effectively than would a full variable tone image. Every image will differ.
It is up to the viewer to determine what is
acceptable, but having enlarged the images, I could begin to detect degradation at JPEG 10:1.
So it clearly becomes an issue of what one is using the images for. My personal agenda is to
retain a "lossless" LZW image as my archive copy and I use any compression for online versions, even JPEG of any ratio--I can always go back to my best quality archive copy. I obviously use a backup method where I am more concerned with image quality than storage space. Digital
storage is going down in cost rapidly, while labor to scan collections can only go up.
Use of JPEG does degrade the image. When you combine this type of compression with lower screen resolutions, such as 72 dpi, images start looking *very* interesting.
Hope this helps. Let me know if anyone has questions.
Robert MacKimmie Curatorial Director of Photography California Historical Society, San Francisco