Jpg compression

Paul Topol

• 2017年12月22日 12:26

When processing pics to jpg I've tried to use the best quality settings:
Quality 100
icc srgb
Resolution 300 px/in
scale fixed 100%

BUT when viewing in Irfanview compression is shown as 6(jpg)

I want better quality than that.
What am I doing wrong?
Thanks
Paul

0

• 

  Ian Wilson

  Moderator

  • 2017年12月22日 12:48

  

  Do you notice any degradation in the image quality?
  
  And my understanding is that JPG quality settings don't really carry over as meaningful numbers between different apps.
  
  You can tell from the file size that setting the quality to 100 in C1 isn’t resulting in much compression. To keep the file sizes down a bit, I usually set it to 85, and I have not noticed a visible difference.
  
  Ian

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  HansB

  • 2017年12月22日 13:44

  The 1st question is: what does '6' mean?
  
  I'm using a software that compresses from 1 (minimum) to 5 (maximum).
  One other software compresses from 0 (none) to 10 (maximum).
  Another software uses quality from 1 (minimum) to 12 (maximum).
  Yet another software uses quality from 1% to 100%.
  CO uses a qupality from 0 (minimum) to 100 (maximum).
  And since Phase One changed CO's jpeg compression algorithm in v10, numbers can't be compared even between old and new.
  
  It could also mean that compression is type '6'. Exiftool lists the 'Compression' for my CO jpeg images as 'JPEG (old-style)'. And there seems to be no other 'Compression' entry in the exif information.
  
  I agree with Ian, there is nothing meaningful in this number unless you know the scale or list it relates to.
  
  
  Regards,
  Hans

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  Paul Topol

  • 2017年12月23日 05:41

  Thank-you gentlemen.
  I'll see what happens when i generate jpg from a tif using photoshop
  
  also see what the pic looks like at 100%, pixilation, etc.
  have great day
  paul

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  HansB

  • 2017年12月23日 09:44

  I found this in the documentation of the exif 2.3 standard:
  

  
  Compression
  
  The compression scheme used for the image data. When a primary image is JPEG compressed, this designation is not necessary. So, this tag shall not be recorded. When thumbnails use JPEG compression, this tag value is set to 6.
  

  
  So it's not a compression ratio.
  
  
  Regards,
  Hans

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  Paul Topol

  • 2017年12月23日 23:10

  thanks.
  i'll check how irfanview sees things.
  
  appreciate your help
  
  paul

  0

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