Why do browsers re-download files when you "save image as"?

Factual Questions
1

Whenever you want to save an image displayed on your browser with the “save image as” option (and I find this true at least for Firefox and IE), it fetches a new copy from the server. But it’s already got a copy, the one you’re looking at. Why doesn’t it just save that one to your hard disk?

I can understand in some circumstances wanting to make sure you have the latest and greatest version of a file, but IME 99.99% of the time the one I’m seeing is identical to the “fresh” one. And if it’s a large image file, waiting for the re-download can be annoyingly time consuming.

So why is it done, and is there a way around it?

2

Because it lets you choose which format you want to save it in usually.

3

The browser obviously has the image in memory, but it may not have the original file in memory. Once the file is decoded, uncompressed and converted into plain bitmap (or some other internal data format), why keep a copy of the original file in memory?

4

[Responding to ChrisBooth12:

I hadn’t thought of that, but it seems not to be true in Firefox, although IE apparently allows you to save in BMP as well as the native format.

But, in principle, at least, that wouldn’t seem to require fetching a new copy of the file. If the conversion routine is part of the browser, you should be able to run it on the version of the file in memory, no?

5

It doesn’t work that way on Safari on the Mac (so maybe Safari on Windows would also work the same way). When I right-click on a image and do a save as, it saves the cached copy.

6

No offense, but are you guessing, or do you know that that’s how browsers operate?

7

I didn’t intend to make any definitive statements about how a browser operates. I was just making an observation, i.e. that the browser doesn’t need to keep the original file in memory.

8

Okay, thanks.

9

When i save a picture I have opened in firefox it doesn’t redownload this picture it just saves the one I’m viewing. I know this for a fact because i can view a 500k picture which takes me ages to open seeing as I’m on dial up. And when i click on save image as it only takes 2seconds for it to me on my computer.

10

For browsers that do have this issue, my guess would be that the cause is simply that different people built the different parts of the browser and it was more of a pain for the guy who was doing the Save As code to figure out a method to verify that the file was in the cache (managed by some other guy, potentially in India), than seemed worth it.