Please Explain

[MOmousefan]

I was reading an excellent article on what is the best file format to save images. When the author addressed JPEGs he made the following statement;

The biggest downsize is that the jpeg format is lossy. Each time you open and save, the image compresses and you lose a small amount of information.
So does this mean that each time I tweak a JPEG and save the result, I lose some of the original content?

 

[AlbertZeroK]

I was reading an excellent article on what is the best file format to save images. When the author addressed JPEGs he made the following statement;

The biggest downsize is that the jpeg format is lossy. Each time you open and save, the image compresses and you lose a small amount of information.
So does this mean that each time I tweak a JPEG and save the result, I lose some of the original content?

That is correct, before you save a jpeg, it compresses it and discards some part of the data. So it is like making a copy of a copy, this is one reason people like to shoot in raw. My raw imagesa actually have more data.

Some formats like tiff allow you the option of saving without loss.

 

[Mosca]

One exception is when you use something like Aperture or Lightroom; your changes aren't made to the original file. Instead, they are saved as a separate database, and the result displayed within the program. Changes are exported as copies of the original, but the orignal and the record of changes are always kept separate. You can always revert the view to an earlier state, nondestructively; you can always view the original file.

http://lightroomkillertips.com/2008/qa-is-lightroom-destructive-to-jpegs/

Sans Lightroom/Aperture (or similar program), you should make a copy of the original file and work with the copy. If you wish to tweak, go back to the original, make a third copy, and tweak... but always save the original.

 

[zackiedawg]

Another exception is that JPEG is a compression format, but nearly all programs have the option to set the level of compression used (the quality as they call it) of the JPEG. It is actually possible to set the compression level to '1', or minimal - whereby you are basically not compressing at all, making loss of data nearly nonexistant.

Most folks would advise though anytime you shoot JPEGs, to always leave the original alone in a file on your computer. Save a separate version anytime you edit or tweak one - the original from the camera stays untouched and if you ever wanted to edit again, try something new, etc, you've got that original you can always open, edit, and then save with a different file name.

If resaving a JPEG, make sure the quality setting is at the maximum (minimal compression) if you want to ensure the least damage to the file. Many programs will default to 10-12% compression, and if you were to keep resaving at that compression level, yes you will lose data and quality quickly!

 

[photo_chick]

I used to be adamant that jpeg is lossy and you shouldn't use it. A lot of people still are. But I can't ignore what I've seen my husband (who is far more skilled in photoshop than I am) do with my jpegs. He's a design guy that detests working with my RAW files, so he grabs from my already exported jpegs when he sees an image he wants to work with.

If you know how to handle the files you are not going to notice the loss from a round or two of editing. You can actually get to the same result as you would with RAW if you know all the ins and outs of it.

I'm not saying jpeg isn't lossy.... it totally is. But most photographers don't know how to handle the files in a way to minimize the loss (and it goes back to how you approach editing and the way those edits affect image quality, not just how you save or how often) so we just say jpeg is lossy and RAW is better.