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View Full Version : JPG > Crop > Save > Degrade?


Nehmo Sergheyev
May 12th, 2004, 01:48 AM
In graphics programs like PhotoShop (I'm using v 8 cs), the general
advice is to interim-save in the app's native file format while working
on a image. If you repeatedly save in JPG, the image degrades with each
save. I understand that saving in PNG doesn't degrade the image since
it's lossless, but you may lose something important to your work, like
layers.

But what if you start with a JPG and then just crop it? Does the save at
maximum quality just save the exact data from the cropped part, or does
it resample and save, thus degrading?

What about other apps? MS Office picture manager and Paint Shop Pro?
What happens when you crop and save in those?

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* Nehmo Sergheyev *
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Chris Schatte
May 12th, 2004, 02:06 AM
Nehmo Sergheyev,
When working in Photo Shop, Digital Image Suite, Paint Shop, Photo Draw or any editing software,
we always save in the native format unitl ready to publish then save to jpg.
This way we always have the native file format if needed for re-edit....

Hecate
May 12th, 2004, 03:06 AM
On Tue, 11 May 2004 19:48:53 -0500, "Nehmo Sergheyev"
> wrote:

>In graphics programs like PhotoShop (I'm using v 8 cs), the general
>advice is to interim-save in the app's native file format while working
>on a image. If you repeatedly save in JPG, the image degrades with each
>save. I understand that saving in PNG doesn't degrade the image since
>it's lossless, but you may lose something important to your work, like
>layers.
>
>But what if you start with a JPG and then just crop it? Does the save at
>maximum quality just save the exact data from the cropped part, or does
>it resample and save, thus degrading?
>
>What about other apps? MS Office picture manager and Paint Shop Pro?
>What happens when you crop and save in those?

It doesn't matter what app you use. Anytime you do anything other than
just open a jpg i.e. anytime you actually do something to the file,
and then resave it, image quality is degraded. Maximum quality doesn't
mean retention of all pixels, it just means the best you can get given
that the image will be downsampled.

--

Hecate

veni, vidi, reliqui

Chris Schatte
May 12th, 2004, 04:41 AM
Precisely the reason that you should have more than one original copy of the file to be edited then published.
When finished, you can use one from your folder/backup to apply the final edits to....

Xalinai
May 12th, 2004, 08:26 AM
On Tue, 11 May 2004 19:48:53 -0500, "Nehmo Sergheyev"
> wrote:

>In graphics programs like PhotoShop (I'm using v 8 cs), the general
>advice is to interim-save in the app's native file format while working
>on a image. If you repeatedly save in JPG, the image degrades with each
>save. I understand that saving in PNG doesn't degrade the image since
>it's lossless, but you may lose something important to your work, like
>layers.
>
>But what if you start with a JPG and then just crop it? Does the save at
>maximum quality just save the exact data from the cropped part, or does
>it resample and save, thus degrading?
>
>What about other apps? MS Office picture manager and Paint Shop Pro?
>What happens when you crop and save in those?

Whenever cropping requires the image to be decoded into a pixelmap and
re-encoded in JPG-blocks there is a chance of degradation.

If the cropping occurs without decoding along the borders of existing
8x8 pixel JPG-blocks ("Lossless cropping") there is no degradation
beyond the existing image condition.

Michael

Nehmo Sergheyev
May 12th, 2004, 10:13 AM
- Kris Zaklika -
> Take a look at Guido Vollbeding's Jpegcrop (http://jpegclub.org/)

- Nehmo -
According to the site, 'lossless' cropping of JPEG images' if you use
(free) jpegcrop for Windows.

I've been opening my photos in MS Office Picture Manager (It opens
quickly), where I do the initial crop. I'm now thinking that's a mistake
(if it resamples than saves). I should initially open with jpegcrop.
Then later when I want to edit, in PSP or PS.


--
*********************
* Nehmo Sergheyev *
*********************

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