Leonard Evens wrote:
The original TIFF file was 5.0MB, as I stated in my post. That was the total for 5 images, indicating that each individual image within the TIFF file was about 1MB.On Sat, 2009-05-30 at 08:00 -0700, James Cobban wrote:I scanned some microfilm yesterday. For some reason the software does not support JPEG so I scanned into TIFF format, putting 5 images in each TIFF file to reduce the number of times I had to enter a file name.When I got home I used GIMP to extract the individual images into JPEGs. Unexpectedly the JPEGs are enormous! For example one of the TIFF files that was 5MB in total, containing 5 images remember, exported into JPEGs which ranged from 9.0MB to 9.6MB! That is using the default 85% quality. This is unexpected since TIFF uses lossless compression while I have indicated to GIMP that I would tolerate some quality loss. Even when I reduced the quality to 65% the JPEGs were still over 5MB each. Are there any suggestions on how I can get GIMP to construct reasonable sized JPEGs?There may be some obvious answer o your question I don't know about. I hope someone provides it. But... It is hard to evaluate your question without knowing some more about the images. What size was the original tiff file?
5088x3096 pixels. This is the same size reported by Image Viewer for both the first image in the TIFF file and the extracted JPEG. The microfilm scanner treats the image as if it was an 11x17" document being scanned at 300dpi.What were the pixel dimensions of the individual subimages which you wanted to save as jpegs?
The original image is a scan of a page from a census. So there should be enormous redundancy in the image. In any event TIFF is able to compress each image to about 1MB using lossless compression, so clearly JPEG should be able to do better. GIMP reports that it takes 75MB to hold the image inside the editor!What size would they be if you saved them as tiff files? Among other things, jpeg only compresses significantly if there is sufficient redundancy in the file to do so. If that isn't so, it is conceivable you might not get that much reduction. How about showing us one of those images?
I have continued experimenting. At quality 3 (3!) and smoothing .85 the JPEG is 604KB and still fairly easy to read. I have put that last version up at http://www3.sympatico.ca/jamescobban/1871_Middlesex_WilliamsW_B3_056.jpg as a demonstration. The quality is acceptable; most of the remaining problems with the image are either due to the poor quality of the original microfilm (the vertical striations) or problems with the scanner (the horizontal striations). I am just astonished that I have to set such extreme quality values to get a reasonable sized file.
-- Jim Cobban jamescob...@sympatico.ca 34 Palomino Dr. Kanata, ON, CANADA K2M 1M1 +1-613-592-9438
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