resolution/jpg quality question

bas1

• 5. Oktober 2007 20:16

Hi,

I am converting my first batches of photo's form my olympus E-500. After trying out the settings for the JPG quality I noticed that the file size decreases dramatically from high to low quality, but the quality of the image does not! I cheked this by zooming in and have the two pictures side by side in C1 LE.

I have the resolution set at 300 dpi. I guess if I change the resolution the quality would decrease. What am I missing? Is the quality button obsolete?

Thanks for your help

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  Ulf Liljegren

  • 5. Oktober 2007 22:00

  Hello
  
  Here is good reading on what a JPG really is:
  http://en.wikipedia.org/wiki/JPG

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  bas1

  • 7. Oktober 2007 11:12

  [quote="UlfLiljegren" wrote:
  Hello
  
  Here is good reading on what a JPG really is:
  http://en.wikipedia.org/wiki/JPG

  
  
  Okay, this is what I understood compression of files would do. Why then do i not notice any change in quality between the files? The only thing i can think of is that my digital monitor does not allow this (I think it is set to 60dpi). Agree?
  
  Thanks, Bas

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  Christopher

  • 7. Oktober 2007 16:14

  Are you changing the JPEG quality setting in Capture One, or your camera? Capture One only processes raw files, but can display JPEG if you have it so enabled.
  
  I'll assume you are shooting raw and then looking at the files inside of Capture One. The thing is, there is no preview of the JPEG compression setting. The image is only passed through the JPEG encoder after it has been entirely processed. That said, even the files output from Capture One at the "Low" setting I would guess are about 70% on the scales of JPEG compressors that run numerically. On photographic data it is still hard to spot artifacts hiding within the rest of the details. But for images with large flat colors and hard edges, like illustrations, 70% would be too low.
  
  If you are indeed viewing your camera's JPEGs inside of Capture One, you probably aren't getting the whole story. Images are scaled to 25% for preview. This is given the label 100% (meaning 100% of the preview data). So 400% is 1:1 of the original data, and you'd need to zoom to at least 800% to make the artifacts visible. JPEG was optimized to fool the human eye into thinking there was no data loss at 1:1--scale up and pattern emerge. It is easier to just compare the files using the zoom of Windows Picture and Fax Viewer.
  
  DPI, by the way, means nothing related to quality when dealing with raster (pixel) based images. It only determines their rendering size at dot-for-dot on various output devices. If you have a file that is 4 inches by 4 inches, at 300 dpi (which would be 1200x1200 pixels). It will appear 12 by 12 on a 100 dpi display, but 1 by 1 on a 1200 dpi printer when every "dot" is used. Capture One only makes a note of the number in the file so another program handling it can get an idea of your intent.

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