Setting Some Things About JPG Format Straight (Page 2): Digging deeply into the technical side of file saving and compression is fine, and good technical information if you want that.

Hyperhad Loc: Thunder Bay, Canada

Digging deeply into the technical side of file saving and compression is fine, and good technical information if you want that. Malarz is trying to simplify the process for those who, right now, just want to know what they are doing when opening, closing, and saving an image file. It is the right place to start, and I suspect that many will understand better what they are doing after reading.

After some familiarity with the process, they can then dig into the subject if they so choose. Simple answers first.

Longshadow Loc: Audubon, PA, United States

LoneRangeFinder wrote:

Most of my programs only ask if you have made a change AND are closing or exiting.

Most programs do function that way. "Closing" the program with no changes should NOT modify the opened file. Clicking "save" is a different story.

Some programs gray out (inhibit) the "save" function until you make a change.

Apaflo Loc: Anchorage, Alaska

rmalarz wrote:

... The jpg format is a lossy file format. ...

JPEG stands for Joint Photographic Expert Group. It defines an image format, not a file format.

JFIF stands for JPEG File Interchange Format. It defines a file format, not an image format.

Reformatting a JPEG image loses image data everytime. Rewriting a JFIF file never loses data.

rmalarz Loc: Tempe, Arizona

Minutia.
--Bob

Apaflo wrote:

JPEG stands for Joint Photographic Expert Group. It defines an image format, not a file format.

JFIF stands for JPEG File Interchange Format. It defines a file format, not an image format.

Reformatting a JPEG image loses image data everytime. Rewriting a JFIF file never loses data.

LoneRangeFinder Loc: Left field

rmalarz wrote:

Minutia.
--Bob

No doubt. That was extremely useful....

rehess Loc: South Bend, Indiana, USA

Apaflo wrote:

JPEG stands for Joint Photographic Expert Group. It defines an image format, not a file format.

JFIF stands for JPEG File Interchange Format. It defines a file format, not an image format.

Reformatting a JPEG image loses image data everytime. Rewriting a JFIF file never loses data.

My computer calls them
filename.jpg

That looks more like 'JPEG' than like 'JFIL' to me.

a6k Loc: Detroit & Sanibel

The OP raises some possible related questions, perhaps unintentionally.

What if you open a JPG, export it immediately to TIF, TIFF or DNG and then make your edits and finally save as the maximum quality JPG?

What if you open a JPG, edit it and then save it as maximum quality?

In my experience, either of these will result in larger file sizes. However, that alone is not proof of non-lossy manipulation. Any experts care to comment?

rehess Loc: South Bend, Indiana, USA

a6k wrote:

The OP raises some possible related questions, perhaps unintentionally.

What if you open a JPG, export it immediately to TIF, TIFF or DNG and then make your edits and finally save as the maximum quality JPG?

What if you open a JPG, edit it and then save it as maximum quality?

In my experience, either of these will result in larger file sizes. However, that alone is not proof of non-lossy manipulation. Any experts care to comment?

If you want experts to comment, I guess you need to post your question over in the "pro" place

http://www.uglyhedgehog.com/s-129-1.html

rmalarz Loc: Tempe, Arizona

The intent of the post was to clarify that editing wasn't necessary to change a jpg file. The Save function alone, without editing, will change the jpg. The post was not intended to open a door into all sorts of machinations that can be done once the file is open. I hope that clears up any misunderstandings and keeps the thread on track.
--Bob

a6k wrote:

The OP raises some possible related questions, perhaps unintentionally.

What if you open a JPG, export it immediately to TIF, TIFF or DNG and then make your edits and finally save as the maximum quality JPG?

What if you open a JPG, edit it and then save it as maximum quality?

In my experience, either of these will result in larger file sizes. However, that alone is not proof of non-lossy manipulation. Any experts care to comment?

a6k Loc: Detroit & Sanibel

rehess wrote:

If you want experts to comment, I guess you need to post your question over in the "pro" place

http://www.uglyhedgehog.com/s-129-1.html

With respect, I do not think that all experts are "pro's" although I concede that the "pro's" are probably experts at what they do. A professional wedding photographer, for example, is not necessarily an expert on the deep-down digital technology. I believe that many of our members are non-professional in the sense of photography yet may be quite expert at their own fields or avocations. Just my 2 cents.

jerryc41 Loc: Catskill Mts of NY

rmalarz wrote:

If one opens a jpg file, looks at it, and saves it, it degrades.
--Bob

So it's the saving, rather than the modifying that creates the degradation. Interesting.

More info -

https://www.thoughtco.com/jpeg-myths-and-facts-1701548

cameraf4 Loc: Delaware

Thanks, Bob. It's been done-to-death on this forum but your explanation should (I hope) settle things for everyone. Very nicely done.

rmalarz Loc: Tempe, Arizona

Thanks, Jerry and cameraf4. I realize this is one of those beat to death topics, but there are just so many misconceptions I hope this clears those.
--Bob

tmac Loc: Northern Kentucky

Ok, so I shoot jpeg. At this point in life, I’m lucky to get the pics to a website where they can be seen and off the camera. I’m a mom taking pics of family and my kids activities. When I download/upload, I go to a couple of places. From card to external hard drive, from card to Shutterfly, and from card to Flickr. Does this degrade my jpeg each time? I mean, is my original on the card degraded? So if I go from card to External hard drive, then card to shutterfly, then card to Flickr, had is degraded 3 Times? Or just one time since I go back to the card to get the image? I’m not even sure my question makes sense. Hopefully someone can figure it out.

Notorious T.O.D. Loc: Harrisburg, North Carolina

There is a book I had probably 20 or more years ago called Graphic File Formats, IIRC. It covered all sorts of information about both lossless and lossy file formats. I do not recall the author off hand. It was sort of the Bible of graphic file formats.

Best,
Todd Ferguson

via the lens wrote:

Does anyone have a technical reference that I could read to find out about this? So far, I have not been able to find anything on this "open and close" issue in my Manual of Photography, which is a sort of bible about technical issues in photography.