JPEG Files: Keeping Originals

**soenda** · 12 March 2007, 05:02 AM

I'm confused about when jpeg files degrade.

I shoot photos in high quality jpeg format. Using a card reader, I download a copy of the whole card in jpeg format onto an external hard drive. They don't get edited or reduced---just copied. For processing, I download a second copy of the whole card in jpeg format onto my hard drive.

At that point, I review the thumbnails in the browse feature of PaintShop Pro 9. I may open a few of them, but I don't rotate them or do anything else. I delete any that are obviously bad. Then I do a batch conversion of the jpegs into psp files for processing.

Here are my two questions:

1. Once in awhile, I mistakenly save a change to the newly converted psp file. That's when I go back to my "negatives" to make a new psp file for editing. When I open and copy a jpeg file, is that an editing process? Am I introducing loss into the original or the new psp file that I make from it?

2. If simply copying a jpeg file does not introduce loss, what's wrong with keeping my "negatives" in jpeg format? They sure take up a lot less space.

Thank you very much for any insight you can offer.

**molucca** · 12 March 2007, 08:50 AM

I have been saving to high quality JPEG, too. Then cropping and resaving. The JPEG from the camera is the sensor data with post processing. RAW is sensor data. I would expect the camera is using compression to reduce the file size, and introduces some loss. Saving the file again with compression would most likely introduce some degregration. This is a question I still have.

I can save the opened file without compression (lossles). The camera must be about 6:1. What happens if I save to the same compression?

No idea what happens when PSP saves to its format.

Rich

**RTK** · 12 March 2007, 01:28 PM

soenda,

Any type of image file will lose data when you run filters on it - or directly adjust it's appearance (colour, shapness etc...) Therefor use adjustment layers when possible. Data is also discarded when "image data" is saved to a lossy image format such as a .jpg again (even at 100%).

.jpg (lossy) ---> brought into Photoshop .psd (lossless as Photoshop Data - unless you manipulate the data/adjust the image directly) ---> saving to .jpg again (you lose data again).

You can save a .psd or .psp file a million times without affecting the quality (if you also don't adjust/change the image data). Adjusting adjustment layers doesn't effect the quality.

Once a .jpg file is brought in to Photoshop or Paint Shop Pro it no longer is a .jpg file anymore - it's just data.

soenda, you don't lose data by opening a file. You also don't lose data by copying a file from one location to another - or making any number of copies of the file. Again, you only have loss when you manipulate the actual data (or save it again as a lossy image format because of the compression).

As for keeping your "negatives: in .jpg format - why not? If it does the trick for you... However, if you have a good camera (or any camera...) that can create files in more than 8-bit RAW, it's technically sounder to keep them as RAW files as they contain more data (that you can manipulate).

Risto

**alanstancliff** · 13 March 2007, 06:27 AM

Originally Posted by soenda

I'm confused about when jpeg files degrade.

I shoot photos in high quality jpeg format. Using a card reader, I download a copy of the whole card in jpeg format onto an external hard drive. They don't get edited or reduced---just copied. For processing, I download a second copy of the whole card in jpeg format onto my hard drive.

At that point, I review the thumbnails in the browse feature of PaintShop Pro 9. I may open a few of them, but I don't rotate them or do anything else. I delete any that are obviously bad. Then I do a batch conversion of the jpegs into psp files for processing.

Here are my two questions:

1. Once in awhile, I mistakenly save a change to the newly converted psp file. That's when I go back to my "negatives" to make a new psp file for editing. When I open and copy a jpeg file, is that an editing process? Am I introducing loss into the original or the new psp file that I make from it?

2. If simply copying a jpeg file does not introduce loss, what's wrong with keeping my "negatives" in jpeg format? They sure take up a lot less space.

Thank you very much for any insight you can offer.

It seems to me that if you do not save the file with the JPEG extension, you haven't altered the original jpeg. If you check the file dates on the jpeg, you'll see that opening them does not change them UNLESS you resave it as a JPEG under the original name.

My camera does the same as yours does. I have all my originals in a "negatives" folder, and when I first open any of them, either to work on them or print them, I immediately save them as a psimage file in another folder before doing anything else.

That little habitual protocol maintains the originals in their virginal and unsullied state, safe in the "negatives" folder cloister

Regards,

Alan

**handrawn** · 13 March 2007, 09:25 AM

a brief summary of lossless editing here: [section 1.5]
http://en.wikipedia.org/wiki/JPEG

**coningham** · 13 March 2007, 01:37 PM

Whenever you save a JPEG you'll lose data, because with every save there is compression.

In order to avoid this, save the file in a lossless format, such as PSP's native .psp or .pspimage (which allows you to keep all your layers for example), TIFF or PNG.

**soenda** · 14 March 2007, 07:28 AM

Okay, I am feeling like the Bear with Very Little Brain. May I try to play back what I've understood, to see if it crossed the confusion barrier?

1. If I run PSP's batch conversion on my newly downloaded jpeg files, I am not opening and resaving the jpeg, so no loss is introduced to the jpeg file.

2. If I need to go back to my "negative" copy, open it and make a second copy of it, that still does not constitute an editing or saving action, so the jpeg is unaltered.

3. As I review the newly uploaded jpegs (this is the second batch, the one that I took from the card reader and copied onto my hard drive), I can open the jpeg file, then close it---without rotating it or editing it in any way---and it will still be in its pristine condition because I didn't save it. Closing a jpeg and saving a jpeg are two different operations.

I'd appreciate it very much if anyone could confirm that I "got" what you've said, or set me straight if I didn't. This is enormously helpful, because I have been making mistakes in overhandling jpeg files AFTER processing them in PSP and reconverting them to jpegs for posting on forums.

Thank you very much for your gracious assistance.

**soenda** · 14 March 2007, 07:30 AM

Originally Posted by handrawn

a brief summary of lossless editing here: [section 1.5]
http://en.wikipedia.org/wiki/JPEG

Aha--I should have known! It's all about rounding errors in the end!

Thank you very much for the link to the article. As I saw the matrices swimming toward me on the screen I thought I was done for, but I found my footing again by the end of the article.

**soenda** · 14 March 2007, 07:36 AM

Originally Posted by molucca

I have been saving to high quality JPEG, too. Then cropping and resaving. The JPEG from the camera is the sensor data with post processing. RAW is sensor data. I would expect the camera is using compression to reduce the file size, and introduces some loss. Saving the file again with compression would most likely introduce some degregration. This is a question I still have.

I can save the opened file without compression (lossles). The camera must be about 6:1. What happens if I save to the same compression?

No idea what happens when PSP saves to its format.

Rich

One of the messages in the Wiki article seems to be that cropping a jpeg, except under certain specific conditions or while using special applications, can introduce loss. It seems counterintuitive, but I think it's one of the mistakes I had been making after processing photos as psp files and converting them back to jpegs. If I understand correctly, unless you have an application specifically for loss-lessly cropping jpegs, you should go back to the editing format---psp, tif, or whatever, to do further adjustments like cropping.

But I'm easily confused, and I could be wrong.

As for the whole compression issue---I'm still working on trying to figure that one out.

**soenda** · 14 March 2007, 07:44 AM

Originally Posted by Risto Klint

soenda,

soenda, you don't lose data by opening a file. You also don't lose data by copying a file from one location to another - or making any number of copies of the file. Again, you only have loss when you manipulate the actual data (or save it again as a lossy image format because of the compression).

As for keeping your "negatives: in .jpg format - why not? If it does the trick for you... However, if you have a good camera (or any camera...) that can create files in more than 8-bit RAW, it's technically sounder to keep them as RAW files as they contain more data (that you can manipulate).

Risto

Thank you for your detailed explanation. Unfortunately, RAW is not an option on the camera I use---Panasonic FZ7---plus, as a relative beginner, I tend to take lots of shots in each session, varying things like f-stop and ISO sensitivity. I use a 2-Gig card, which allows me to bring home 340+ high quality jpeg files per session. I'm afraid that if I was shooting RAW files, I'd use up the card space so much more quickly, it would be like going back to film...at least that's my current impression.

I really appreciated your reassurance about being able to save and resave. Thanks.