Google| Subject | Re: Lenses and sharpening |
| From | Eric Stevens |
| Date | 09/18/2014 07:05 (09/18/2014 17:05) |
| Message-ID | <pdok1ah1f8khn8chkh5gcpbqucqj5gotq8@4ax.com> |
| Client | |
| Newsgroups | rec.photo.digital |
| Follows | Savageduck |
| Followups | Savageduck (1h & 5m) Sandman (3h & 29m) |
On Wed, 17 Sep 2014 19:20:02 -0700, Savageduck <savageduck1@{REMOVESPAM}me.com>wrote:
SavageduckYes, 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.
On 2014-09-18 01:00:46 +0000, Eric Stevens <eric.stevens@sum.co.nz>said:Eric StevensSavageduck
On Wed, 17 Sep 2014 06:05:14 -0700, Savageduck <savageduck1@{REMOVESPAM}me.com>wrote:SavageduckEric Stevens
On 2014-09-17 09:22:00 +0000, Eric Stevens <eric.stevens@sum.co.nz>said:Eric Stevens
On Tue, 16 Sep 2014 22:27:43 -0700, Savageduck <savageduck1@{REMOVESPAM}me.com>wrote:Savageduck
On 2014-09-17 04:08:19 +0000, Eric Stevens <eric.stevens@sum.co.nz>said:Eric Stevens
On Tue, 16 Sep 2014 07:53:15 -0700, Savageduck <savageduck1@{REMOVESPAM}me.com>wrote:Savageduck
On 2014-09-16 10:36:29 +0000, floyd@apaflo.com (Floyd L. Davidson) said:
--- snip ---Eric StevensSavageduckSavageduckEric Stevens
The reverse process performed on a lossy, compressed JPEG is not going to reverse the HPF to return to the original state. That was lost once the save was executed.
That's why I never included a conversion to JPG in my example of a reversible process.
?but that genius Floyd did.
--- snip ---Eric StevensNo one who understood what we were trying to talk about would claim that a JPG conversion is a reversible process.Savageduck
?but that genius Floyd did.
I've had a look and I cant see where. Could you refer me to the message?
With pleasure.
That wasn’t too tough to find: Posted: Mon, 15 Sep 2014 13:44:18 -0500 Message ID: <8738bs2076.fld@barrow.com>
Wherein Floyd stated the following:
“A non-destructive workflow means you can *undo* and then *redo*.
That is not a reversible function.
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.
If the sharpening is done with UnsharpMask that cannot be done. USM is not reversible.”
Note, the words, “save it as a JPEG,”.
As I said, that genius Floyd did.
Based on what Floyd has been saying all along, the obvious series of processes would be:
1. Sharpen image.
2. Save file as TIFF
3. Apply Gaussian blur to TIFF image to recover original image sharpness.
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.
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.
... 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 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. 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.
--
Regards,
Eric Stevens
09/13/2014-
