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March 01, 2007
Image Differences That You Can't See : Jared as Creative Director of New Media
I'm often asked what is the practical difference between scanning a slide at 8 bit verses 16 bit or saving a TIFF verses a JPG with quality set to 12.
For all practical purposes there isn't any difference and normally when comparing them in Photoshop using a difference filter the naked eye sees nothing out of place. In fact most of the time the comparison images are pure black.
However...
I was asked by a patron about what the human eye can't see. So instead of just overlapping the images in Photoshop and running a difference to see what pixels, if any, looked out of place - I decided to flatten the image and then run an Equalize Adjustment on it to stretch the data into a range into which I could see the differences.
For this posting I reduced all of the resulting images from 5400 pixels to 1000, from 16 bit to 8 bit, and from TIFF to JPG Quality 12. The images are still a good representation of the previously unseen differences without uploading images that are 130MB each.
Let's start with this photograph that I took in Ireland:
This is the exaggerated difference between the 16 bit image and the 8 bit one:
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This is the exaggerated differences between the 8 bit TIF and the 8 bit JPG saved at quality 12:
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This is the exaggerated difference between the image using single line sampling an image sampling 16 times per line:
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This is the exaggerated difference between the digital ICE set to normal and the digital ICE set to fine:
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In the end I am fascinated by the amount of data that is being lost in each of these cases. For my own archives I've been saving the originals as 16 bit TIF files with the Digital ICE set to normal. But I wonder if I should look more into the 16x sampling mode as well as the Digital ICE fine mode.
I also like the similarity in the 'look' of the differences between the 16x sampling comparison and the Digital Ice comparisons.
Coming soon: A look at the differences that you CAN see: ICE, GEM, and JPG.
Posted by jeb2 at March 1, 2007 07:40 PM
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Comments
Is there a photo missing? I seem to have gotten lost in the comparisons.....
Posted by: Charack at April 28, 2007 02:20 AM