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Re: Lenses and sharpening

Sandman
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SubjectRe: Lenses and sharpening
FromSandman
Date2014-09-18 10:34 (2014-09-18 10:34)
Message-ID<slrnm1l6p4.881.mr@irc.sandman.net>
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Newsgroupsrec.photo.digital
FollowsEric Stevens
In article <pdok1ah1f8khn8chkh5gcpbqucqj5gotq8@4ax.com>, Eric Stevens wrote:

Savageduck
As I said, that genius Floyd did.

Eric Stevens
Yes, I found that text, but I don't think that it means what you seem to think it means. He wasn't claiming that JPEG is fully reversible: everybody knows that it isn't.

He did make this claim:

Floyd L. Davidson Re: Lenses and sharpening 09/15/2014 <8738bs2076.fld@barrow.com>

"For example, you can add sharpening with a high pass sharpen tool to an image, save it as a JPEG, send it to someone else, and they can use a blur tool to reverse the sharpen."

That is an *incorrect* statement. When you have added JPG compression to the file, the "someone else" *can not* reverse the HPS effect with Gaussian Blur. The end result may be *similar* to the original image, but the effect will *not* have been reversed.

Floyd is very very ignorant about these things. You really should stop playing in his corner.

Based on what Floyd has been saying all along, the obvious series of processes would be:

1. Sharpen image.

2. Save file as TIFF

JPG you mean. That is what he said.

3. Apply Gaussian blur to TIFF image to recover original image sharpness.

Applying GB to the JPG will *not* reverse the HPS, contrary to this incorrect claim.

This series of processes is possible if you sharpen with a high pass filter but not possible if you sharpen with unsharp mask. i.e. the original image is recoverable if you sharpen with the high pass filter.

Not using Floyd's method, no.

Floyd then went further and, as you quoted, proposed an alternative series of processes:

1. Sharpen image.

2. Save file as JPEG

3. Apply Gaussian blur to JPEG image to recover original image sharpness.

This is the only method Floyd has suggested. He never talked about TIFF's.

... and claimed that, again, this process also is possible if you sharpen with a high pass filter but not possible if you sharpen with unsharp mask. i.e. the original image is recoverable if you sharpen with the high pass filter.

I.e. he made an incorrect claim, he doesn't know what "reversible" means and has no idea that JPG adds compression. No surprise there.

I understood him to be saying that inspite of the losses of a JPEG conversion, recovery of the original sharpness is possible if the original sharpening process used a high pass filter.

It may look similar, but the effect is *not* reversed. At most, it is counteracted.

That while saving as a JPEG will always cause losses, this will not prevent a Gaussian blur operation from recovering the sharpness of the original image.

Indeed it will.

-- Sandman[.net]