Compression question

[macroMe]

Hi guys,
I recently heard that each time I open and close a photo that every close action results in further compression. Like to the point where after looking at a photo oodles of times you can actually see the degradation of the image. Any opinions? The person who told me this was talking about how they store their images - they keep the original in a completely separate folder then make a copy from there that they work on and/or use for presentation, thus ensuring the original is never opened or closed so never subjected to any compression.
If this is true does anyone know if the mac i-photo program actually opens and closes the image or does it effectively just show a larger thumbnail? As in does looking at photos in i-photo result in compression?
Any thoughts on this dilemma appreciated.
Thanks.

[Japaslavian]

An image will become further and further compressed if it's a JPEG and you open it in a program and re-save it. Each time you save (save being the operative word) a JPEG, it will become little-by-little more compressed.
PSD's will not, as well as some other native file types.
If you just look at it and close it again, it won't do anything.

[macroMe]

Originally Posted by Japaslavian

Each time you save (save being the operative word) a JPEG, it will become little-by-little more compressed.

So does this mean that opening and closing it does nothing unless you actually save it, as in make a change then save?
Also with the PSD format would that mean that saving the originals as PSD files will keep them safe from compression?
Thanks.

[Japaslavian]

Originally Posted by macroMe

So does this mean that opening and closing it does nothing unless you actually save it, as in make a change then save?
Also with the PSD format would that mean that saving the originals as PSD files will keep them safe from compression?
Thanks.

Yes and yes.
Though understand that the fact that the camera has saved the image as a JPEG to begin with means the image has been somewhat compressed before you even move it to the computer. That's where RAW format shooting comes in and is arguably (though I couldn't be bothered by it) the best way to shoot images.
But that's a whole other can of worms.

[macroMe]

Thanks heaps for that. You have just been responsible for an "Ah ha" moment halfway around the world
Got it sorted in my head now. Appreciate the info.

[milosh]

Originally Posted by macroMe

So does this mean that opening and closing it does nothing unless you actually save it, as in make a change then save?

Yes. To clarify this a bit more, let's take an ordinary image viewing program (like Windows Image and fax viewer for example). Your image is stored on your hard drive and when you open it (in order to view it) the program that is associated with that function loads itself in the operating memory of your computer and then it also loads the image you clicked on to operating memory (it literaly copies the image from hard drive to a temporary location in operating memory). So, the image you're viewing is actually in the operating memory (during that time while you view it). When you close the image viewing program, it erases that image from the op. memory and it also erases itself from the memory. So, no writing is being done to the hard drive, that means the image isn't being edited. But. if you open it with some kind of an editing program and save it, then it's edited.
Sorry if this is too confusing.

[OsmosisStudios]

Originally Posted by milosh

When you close the image viewing program, it erases that image from the op. memory and it also erases itself from the memory.

This assumes the program writer made sure to destroy(); the temporary file before exiting. Which for windows can be hit or miss...

[milosh]

Originally Posted by OsmosisStudios

This assumes the program writer made sure to destroy(); the temporary file before exiting. Which for windows can be hit or miss...

That's right, each program should cleanup after itself, but some don't..