Hi prjohn and welcome to AlphaMountWorld,

Copying and or moving a JPG will not affect the quality of the file. It only degrades after opening and closing it. This is because closing it will re-compress the file (throwing away detail), do it often enough and the image will turn to mush! If you are going to save a file as a JPG it is best to save the finished version (i.e. one that will not need opening too many times) or better still, save the file as a PSD or TIFF.

Hope that helps,

Andrew

Andrew your answer makes me wonder what happens when I send my JPG to flickr where others can open it or download it many times. Are they really copying not opening it when it's viewed on Flickr?

Dave

Hi Dave,

On the topic of Flickr, I am not 100% sure, if they are downloading the file then I'm sure they are copying it-otherwise after a while the file would look pretty crummy. As for viewing it I would imagine the file is imbedded into the web page and therefore remain open. Good question, and perhaps there is someone with a more definitive answer with regards to Dave's question.

Andrew

Andrew,

Just so I understand, I think when you said "open and closing" you may have meant "opening and re-saving" the image. That is, if the software just "reads" the JPG file, there are no changes to the file. When you re-save the image, you re-write over the original file. If the software re-saves the file, then the software will re-compress the JPG file as it writes over the original JPG file. Re-saving JPGs, especially using different software may cause degradation of the image.

So, bottom-line: just reading a file - no changes. Re-writing a file, changes occur. Am I interpreting what you said correctly?

That being said, I can understand, why you chose the word "close". I believe you said it because most people will choose to accept the changes to the file when they close the file - essentially re-writing over the original file.

Dave,
Regarding flickr, their applications seem to make one change to the JPG file upon receipt of the original JPG image.

However, when it presents the JPG image file to the web, there are no more changes. Also, you aren't actually looking at their 'master copy' anyway. They always keep the 'master copy' of your JPG file on their data storage hard drive and provide an exact, but temporary copy on a separate computer, their web-server

When you browse to that web-server, your web browser will make an exact copy of their web-server's JPG file, and your browser will present that final copy to your monitor. The master copy JPG, unchanged, is still on the flickr hard drive in their data centre.

Also, your web-browser never really opens(reads) and re-saves(writes) a file in the way Photoshop might open(read) and re-save(write) a file. Like most image *viewing* software, your web-browser just reads a JPG file, makes an internal copy for itself, presents that internal copy to you. When it's done, your web browser throws away the internal copy - it doesn't re-write over the original.

Assuming only one person has ever looked at that image file from flickr, then there are about four copies of that image -

1. the original JPG from the original photographer on their own personal hard drive
2. the new "master" copy of that JPG on the flickr storage hard drive
3. a temporary copy that the flickr web-server borrows from the flickr storage hard drive
4. another temporary copy of the JPG file that is sitting in a temporary folder on the web-surfer's hard drive.

There are actually a few more steps and few more copies of that information, but this is the conceptual flow of your JPG file.

I tried to say that in non-technical language - Did it make sense?

Like so many times in my life, the act of formalizing a question when I write it done clears it up in my own mind. Shortly after I posted the question I thought to myself, There is no "save" involved when we view in on the Web page. Thank you for confirming my thoughts.

Dave

Hi b shaw,

Yes I meant saving rather than simply closing the file. You did a better job of explaining this than me so cheers.

Andrew