Technical Question About JPEG Quality Loss

[BekahAura]

I know I've read that every time you open and save a JPEG image you lose a little bit of quality... I'm wondering if this goes as far as simply opening the image and closing it without making changes or saving. What about viewing the image in my Windows picture viewer (or whatever it's called)?

I often look over images that I've already edited and saved as JPEGS. Lately I've been saving all of my photoshop documents, and I just started shooting raw, so I have a backup plan now. I'm just concerned about my older photos that I shot in JPEG.

I have a bulk folder of the original files, and I copied the best ones into a new folder to be edited, so technically I never altered them right? I do occasionally look over the originals to see if I've missed anything, am I hurting the files by doing this?

I just want to be clear, any help would be appreciated =)

 

[Big Mike]

No, simply viewing an image will not harm it.

You loose quality when saving a JPEG...but realistically, a jpeg can be saved over and over again before you really start to notice a difference.

 

[Jace]

On a related note, I save all of my files, after finishing with their touch-ups or what have you, in .PNG format, is that bad?

 

[KmH]

It depends what you want to use the files for.

PNG was designed for images that contain text, line art, or graphics, and is intended for transferring images on the Internet, not for print graphics, and therefore does not support non-RGB color spaces.

PNG, like JPEG is an 8-bit depth file format, but it is a lossless format, unlike JPEG. Being an 8-bit depth file, there is little editing headroom if you want to revisit a file and change the editing.

I save my files as 16-bit depth .PSD files (including the layers) so I can go back in, make a duplicate of the file, and completely re-edit an image if needed.

PNG has no standard for supporting EXIF data.

 

[hrry]

Shoot RAW.

 

[KmH]

I know I've read that every time you open and save a JPEG image you lose a little bit of quality... I'm wondering if this goes as far as simply opening the image and closing it without making changes or saving. What about viewing the image in my Windows picture viewer (or whatever it's called)?

What you are asking about is called 'Generation Loss':
Generation loss - Wikipedia, the free encyclopedia

 

[BekahAura]

Thanks a lot guys... I feel better now, seeing that you'd have to resave the image dozens of times to see a noticeable difference.

Keith: Thanks for mentioning how many bits you save your files at. I wasn't sure what the difference was between 16-bit and 8-bit, but now I will definitely save 16-bit PSDs instead of 8-bit.

In case anyone else is interested, find out about the difference between 16-bit & 8-bit here: 8bit-versus-16bit-difference