RE: filmscanners: File format

["Shough, Dean" <dean.shough@lmco.com>]

> Your results will vary depending on the image you use. I hope this data is
> useful. Your conclusions will vary depending on your needs obviously.
>

I did a similar test using a 1k by 1k piece out of the PhotoDisc test image.
The original image is extremely sharp and contains nice flesh tones and high
contrast, fine details.  I compressed the image using Photoshop and Boxtop's
ProJPEG software.  For each save, the ProJPEG settings were 50% and no
smoothing.  After each save the image was closed then reopened.

>From my original 1k image I will show a 128 by 128 pixel crop, picked
because it had the worst JPEG artifacts.  The image is mostly fine black
hair against a white background, compressed using the 50% settings:

 <<OriginalImage.jpg>> 
Looking at the difference between the original image and the first
compressed image reveals mainly noise.  The level of the noise increases in
areas where the original image had fine detail.  The following image was
generated by using Photoshop's "Apply Image" command with the blending set
to "Subtract", the scale at 1 and the offset at 128.  I then used the levels
command with the levels set to 102 and 152 to increase the contrast so that
the difference could be seen.

 <<DiffOrig-01.jpg>> 

Repeating this for the difference between the first and second compressed
images produced NO differences in most areas with a few blocks containing
low frequency, low amplitude differences:

 <<Diff02-01.jpg>> 

Repeating yet again for the difference between the second and third image
produces a similar image with fewer block being different and the
differences being smaller:

 <<Diff03-02.jpg>> 

Somewhere between the third and tenth image the differences completely
disappeared.  The difference between the original image and the 10th image
is hard to distinguish from the first difference:

 <<DiffOrig-10.jpg>>

Attachment: OriginalImage.jpg
Description: JPEG image

Attachment: DiffOrig-01.jpg
Description: JPEG image

Attachment: Diff02-01.jpg
Description: JPEG image

Attachment: Diff03-02.jpg
Description: JPEG image

Attachment: DiffOrig-10.jpg
Description: JPEG image