Maybe you are doing nothing wrong. If there is no difference between the
images, you will get 000 for red, green and blue channels at each point
after subtracting the JPG image from the TIF image.
If there is more than one spike, you put one triange on each side of the
spikes in levels it will amplify any differences. I'll send you some example
files.
Jack Phipps
-----Original Message-----
From: Stan Schwartz [mailto:snsok@swbell.net]
Sent: Monday, February 05, 2001 9:15 PM
To: filmscanners@halftone.co.uk
Subject: RE: filmscanners: Re: Scanning problems
Jack,
I tried this on a 50 MB tiff image. After following your instruction, the
histogram shows a single spike adjacent to the left border of the histogram
box directly above the black arrow. Adjusting the levels arrows doesn't do
anything. All the subtracted pixels are black. What am I doing wrong?
Stan Schwartz
-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Jack Phipps
Sent: Monday, February 05, 2001 4:43 PM
To: 'filmscanners@halftone.co.uk'
Subject: RE: filmscanners: Re: Scanning problems
Julie--
Do you have a high resolution scan in a TIF format? If you save it as a JPG
in Photoshop at the highest quality and open it up again (so you have two
images open in Photoshop, the original plus the image saved as a JPG), and
then do an apply image, applying the JPG image to the TIF image, blending
using subtraction, the result will be the difference between the two images.
At first glance, it will be black. But if you do a level, the histogram will
so some information at the very left. Slide the triangles over to amplify
the differences.
So what? Well, if that small amount of difference is important to you, you
should insist the negatives be rescanned and saved in a format that will
retain all of the image information. Also, you don't know if they saved at
the highest quality or not. It is also a good way to show to the lab that
yes, you do loose something at the highest quality setting. And it could be
a good way to convince yourself that you can live with their result.
By the way, I've just now run a test and I've saved a small part of an image
that takes up about 700 kb. I was going to attach the results but I didn't
know if that is allowed on this list. Should I do that or is there an
archive where I can post the results. I would be glad to send them to you
Julie in a separate email.
Anyway, good luck with your project.
Jack Phipps
Applied Science Fiction
-----Original Message-----
From: Cooke, Julie [mailto:CookeJ@logica.com]
Sent: Monday, February 05, 2001 8:15 AM
To: Filmscanners@Halftone. Co. Uk (E-mail)
Subject: filmscanners: Re: Scanning problems
I've just had my 6x7 trannies scanned by a lab specialising in digital. I
paid for a 50MB scan and got a 7MB jpeg back. I took the CD back to the
manger, who told me that it was a 50MB scan, compressed to 7MB and that all
the information would be there when I opened it up!!! I think by this he
means that when you go to Image Size in Photoshop it does say 55MB (4800
pixels x 3900 at 300dpi), although the file is 7MB. Is this the file size if
saved to psd format? I've lent my Real World Photoshop book out.
I explained that jpeg was a lossy compression, that information had been
lost when converting to jpeg and it was no good to me. He looked at me as if
I was mad and said that he uses jpeg for all his customers to get more
images on the CD. I argued that jpeg does loss information and drops the
colours that the eye cannot see. He told me that I had to specify tiff
otherwise he saves as jpeg, then reluctantly said 'so you want me to do the
whole job again'.
This lab specialises in digital, how can people accept jpegs? So much
information has been lost for manipulating (levels and curves) in
Photoshop. I won't be going back there again...
Julie
