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Old Jan 7, 2009, 9:16 AM   #1
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The title should red: Does save with new file-name have a negative impact on IQ?

Usually I batch-rename my daily newphotos when transferring them from the Memory Card to my PC. The new file name is generated by a program, to something like: 2009_01_07 + a sequential 3-digit number added on with a hyphen in between.

Lately I have become increasingly paranoid aboutloosing Image Quality by re-saving JPG-files. I think I have read somewhere that a JPG-file will loose quality, every time it is saved. (?!?!)


Is that correct, or does it only apply when one has actually changed something in the file itself (like changing contrast, for instance)?



How do you transfer and organize your precious files?




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Old Jan 7, 2009, 9:55 AM   #2
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Walter_S wrote:
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Lately I have become increasingly paranoid aboutloosing Image Quality by re-saving JPG-files. I think I have read somewhere that a JPG-file will loose quality, every time it is saved. (?!?!)
Sort of.

JPEG files are compressed using standard compression algorythms. The compression method is not loseless, so some detail will be lost the first time an image is converted to JPEG (as in, in your camera.) Each time the image is opened in an image editor, some of the original detail has been lost from the initial compression, so when it is saved again, a little more detail may be lost as it is compressed again.

But when you save a JPEG image, you can choose the level of compression, and selecting the least amount of compression means that you would have to resave the image hundreds of times before you actually see the difference. ANd once the image has been compressed to a greater level, the lost detail can never be recovered.

Teh best technique is to preserve your original images as they came out of the camera, and only process copies of those images. "Save with new file-name" does that.
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Old Jan 7, 2009, 3:13 PM   #3
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Thank you TCav!

Appreciate you taking time to answer this.

As for files that are adjusted / altered / cropped, etc. it goes without saying that one saves with a different file-nameto keep the original-one as "virgin" as possible.

What about a 90º rotation, to upright a portrait-format, for instance. Is the pixel-deterioration measurable or is thisneglect-able?


I never really thought of this until recently, when my new camera suddenly produces beautiful shots (at 3-4 Mb per shot) with 10Mp resolution wit such details, and now I want to take care of ever pixel!

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Old Jan 7, 2009, 3:29 PM   #4
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The procedure I have been using to avoid losing quality with multiple saves is ......

As soon as I download the images from camera to computer, I save as a "tiff" file and make a copy. I then do all the editing and post processing that I want and save as "tiff" as often as I need without losing quality. Once I am satisfied with the edited image, I save as a "jpeg" file. I hope this makes sense! :-)
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Old Jan 7, 2009, 4:50 PM   #5
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Walter_S wrote:
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What about a 90º rotation, to upright a portrait-format, for instance. Is the pixel-deterioration measurable or is thisneglect-able?
Actually, when you take a photo, the orientation of the camera is usually stored in the image. Rotating it and saving it will cause the image to deteriorate, but no more than saving it for any other reason.

If your image editting program doesn't recognize the orientation, and doesn't properly display the image, it's possible that your camera doesn't store that info in the image, but you might try a different image editting program.
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Old Jan 15, 2009, 10:02 PM   #6
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I create a bak folder, save all original pics as ZIP files into it,
and then edit jpegs. Yes, it creates double files, and more space
is used, but you have orig files.

Whether the pics are stored as zips seperately or in single file, is up to you.

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Old Jan 15, 2009, 10:11 PM   #7
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romphotog wrote:
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I create a bak folder, save all original pics as ZIP files into it,
and then edit jpegs. Yes, it creates double files, and more space
is used, but you have orig files.

Whether the pics are stored as zips seperately or in single file, is up to you.
Since JPEG files are already compressed, compressing them again in a ZIP file can actually take up more disk space. But storing them in a single large ZIP file can make up for it.
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Old Oct 26, 2009, 2:37 PM   #8
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Default Does "save with new file-name" have a negative imp

Revisiting this thread, here is a stupid question ... when we talk "save" are we talking about opening up and making edits vs. actually viewing the file in say Picassa? When we open it up in an image editor but don't save it, does that have an impact? Thanks!
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Old Oct 26, 2009, 2:42 PM   #9
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If you are just copying a file (or renaming files), that's not going to impact image quality (since no editing or recompression should be taking place). If you do open a file with an editor and resave it, then it's probably being recompressed (based on the JPEG Quality settings you have set in the editor you're using).

I'd suggest that you take a look at this article:

JPEG Images: Counting Your Losses by Mike Chaney
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Old Oct 26, 2009, 2:47 PM   #10
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Quote:
Originally Posted by mdezrin View Post
When we open it up in an image editor but don't save it, does that have an impact? Thanks!
No. If all you do is open it up, there's nothing to save. But because JPEG files are compressed, and opening them uncompresses them, an image editting program will give you the option to save the newly uncompresses image, either as a JPEG for which it will be compressed again, or in some other file format, such as PNG,
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