JPEG Files: Keeping Originals

[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.

[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

[soenda]

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.

[Trev]

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.

Well you can not crop losslessly as cropping cuts of some of the image, but if you save as jpeg then depending on how much compression is used then some pixels are noted as to there position and colour the discarded. Hence the lose. When the image is opened those pixels are painted in but are not the original. doing this over and over will gradually produce rubbish. So save your originals in a save place and even mark as read only if you want the only work on a copy after all your enhassment you could save it in lossless format PSP, PSD, Tiff or png Ect. and then do a resize if need be and save as .jpeg for the web. And incidentally rotating a jpeg by increments of 90 degrees is lossless as no pixels are changed only resorted.

[soenda]

Well you can not crop losslessly as cropping cuts of some of the image, but if you save as jpeg then depending on how much compression is used then some pixels are noted as to there position and colour the discarded. Hence the lose. When the image is opened those pixels are painted in but are not the original. doing this over and over will gradually produce rubbish. So save your originals in a save place and even mark as read only if you want the only work on a copy after all your enhassment you could save it in lossless format PSP, PSD, Tiff or png Ect. and then do a resize if need be and save as .jpeg for the web. And incidentally rotating a jpeg by increments of 90 degrees is lossless as no pixels are changed only resorted.

So you really can rotate the jpegs 90 degrees without loss? Cool! I saw this as I was researching the whole lossy jpeg issue before I posted my original question. But I put it in the "too good to be true" category.

It would save a lot of time if I could batch rotate all my portrait format shots on my first pass of the jpeg files. I generally look for duds before doing the conversion to psp files, but sometimes without rotating the file I can't tell the keepers from the tossers. If there's no loss from 90 degree rotation, then I won't waste time converting duds I could eliminate as jpegs.

Thanks very much, Trev.

[remi]

It would save a lot of time if I could batch rotate all my portrait format shots on my first pass of the jpeg files.

The free image viewer IrfanView is able to rotate your JPEG files losless:

1. Start IrfanViews thumbnail viewer
2. Select all the files you want to rotate
3. Press "Shift+J" and select the option "Auto-Rotation (by EXIF information)" and IrfanView interpretes the rotation information, saved by your digital camera within the JPEG file and rotates all your images into the right angle (horizontal to vertical or vertical to horizontal) - losless.

Regards,
Remi

[RTK]

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

[coningham]

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]

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.

[alanstancliff]

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.

What do you mean by referring to your brain as "little brain"? Your questions show that you're plenty bright enough to ask a lot of questions and analyze. No one can count that as stupid.

Try this:

1. Open one of your "negatives," i.e., a JPEG
2. Immediately go to FILE and click on that
3. Then click on the SAVE AS option from the drop-down list
4. A dialog comes up with two boxes you can enter text in, FILE NAME and SAVE AS FILE TYPE. Click on the drop down next to FILE TYPE.
5. Select PSPIMAGE or PSP (or any other lossless format)

You have just saved the file without disturbing the original JPEG. Do that every time you open the original JPEG without fail. Do not save it as a JPEG with the same name.

After you have finished tarting up the photo, you can export it or save it as a JPEG, but use a different name than the original "negative's" name.

Give us a holler if you need more clarification.