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JPEG Image Quality

This is a menu of the topics on this page (click on any): The Quality of the Source Image    The Quality of the Scanning Equipment    Processing Care    Resolution    Compression   .

The Quality of the Source Image

Without a doubt, the skill and equipment of the photographer are the most important determinant of image quality. This image is an exceptional shot of Tracie Moll by Sasha Mitelman. Click on it to see it larger; then click "back" to return to this page.

Here's Sasha's recollection on how he made this shot. Photo equipment was (all canon) eos 1N body, 400mm f/2.8 lens with 1.4X teleconverter (resulting in an effective focal length of 560mm at f/4), and a monopod. Exposure looks like it was in direct front light at mid-day, so that would be somewhere around 1/1600 sec. at f/4 on ASA 100 film. this was most likely shot on slide film, either Fuji RDP-II or Kodak E100S.
As far as composition goes, to get out past 3 or 4 lanes into the pool you really need 400mm or longer (a 300mm lens works OK out to lane 3, but is too loose if you go any further). I normally try to pick a spot with decent light and a clean background, then just wait for the swimmer to get there. In this case they had set up two 8-lane courses across a 50m pool, so shooting from the side (where there was at least 30-35m of clean background behind the subject) worked better than shooting from the end of the lane."

The Quality of the Scanning Equipment

The first image (of Anne Grams) was scanned on an HP Scan-Jet 3c at Kinko's while the second was scanned by Swim Magazine's lab, PC Graphics, on their $150,000 scanner. The Kinko's scan was then processed for the web on PhotoShop 3.0 at a height of 375 pixels at 150 pixels/inch of resolution. The PC Graphics scan was processed in Paint Shop Pro 6.0 to a height of 375 pixels at 72 pixels/inch of resolution. (Be warned that web sizes do not look the same in Paint Shop Pro as they are displayed in "print size", but they become the same when displayed in IE5 which seems to be governed by pixel size.)

The above test with the image of Anne Grams is a replacement for a test on Tom Meade's photo which was less conclusive. The first image (of Tom Meade) was scanned on an HP Scan-Jet 3c at Kinko's while the second was scanned by Swim Magazine's lab, PC Graphics, on their $150,000 scanner. (The PC Graphics scan is a 3,611,878 byte tif file. Both were then processed for web use using PhotoShop 4.0 at a height of 350 pixels, resolution 150, and level of quality 1 (lots of compression). Just for fun, I then reduced the resolution to 72 and saved it again. File sizes are 15910, 17849 and 15905 respectively. Unfortunately, my PhotoShop 4.0 installation has become defective so IE5 can't open it's files, though they look fine in PhotoShop and Paint Shop Pro. Rather than install PhotoShop again, I used Paint Shop Pro 6.0 from Jasc and repeated the process. The image looks the same as the PhotoShop image, but Paint Shop Pro has greyed out the field for "resolution" and the save produced a file of 22334 bytes. This is informative; resolution did not make much or any difference in file size or appearance with PhotoShop 4.0; Paint Shop Pro greys it out, asks no question on "level of quality", and saves the file at a byte size that seems equivalent to PhotoShop's "level of quality 3", "medium compression" (based on file size). (This comparison has been replaced by the test with Anne Grams image. The tif file that resulted from the PC Graphics scan of Tom Meade's photo was only 435,366 bytes, in addition to the problems noted above.)

Processing Care

Here's the same image as scanned by PC Graphics and batch processed with Jasc Image Robot with height set to 300 pixels. This is the process by which we are creating our Library of Swim Magazine Photos.

Resolution

The section above on Tom Meade's photo indicates that resolution may not mean much for web images. The fact that Paint Shop Pro greys it out for web images reinforces that conclusion. The next section on compression using the photo of Tracy Grilli suggests that level of compression does not seem to mean much in image quality, though it sure means a lot in file size. Paint Shop Pro does not give you a choice on level of compression; it's default appears to be equivalent to PhotoShop's level "3" (medium).

Compression

A single image (a very high quality photo of Tracy Grilli by Tom Lyndon) was scanned on an HP Scan-Jet 3c with resolution set at 150 pixels per inch and image height set to 350 pixels. It was saved in .psd format with a file size of 303,072 bytes. Then it was converted to .jpg format under each of the four image quality options presented by Adobe Photoshop 4.0. When it was saved with "low" (1) image quality, the file size was 14,582 bytes. When it was saved with "medium (3) image quality, the file size was 19,856 bytes. When it was saved with "high (6) image quality, the file size was 33,391 bytes. When it was saved with "maximum (8) image quality, the file size was 67,418 bytes. Each of the four files are displayed below (in the above order).

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