Hedge neighbor

I know that changes to a JPEG image are not lossless because of the way they are compressed and I am OK with that because I make the changes that I need once and then that is my permanent final version of the photo. But I often change the file name and especially add keywords to the files as I review them. I have not been able to find an answer to my question if those changes to the non image part of the file cause any degradation to the picture itself - in which case I would change my photo processing workflow. Does anyone know of a definite answer to this? Thanks

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Opening and saving a jpeg causes a decompression/compression cycle, and that is what eventually degrades the image. If you use a metadata editing program like EXIF Tool, which does not open the file, I suppose the edits will not affect the image.

On the other hand you have 1000% more flexibility with raw files, which do not become images until you convert them.

To me, keeping a jpeg of an image as a record copy is like tossing the negative in film, and just keeping a paper copy of the print. I'd rather have the negative. Technology is constantly improving. Images that I edited in RawShooter in the early 2000s look remarkably better when I use the current versions of Capture One, DXO PHotoLab, Lightroom, ON1 PhotoRaw, etc. I'd hate to just have a jpeg of any of my images.

lbuhle Loc: Media, PA

Metadata tags are not compressed, but some programs do remove meta-data (e.g. F-stop, GPS data, copyright info). Sometimes this is desired for privacy reasons (e.g. removing GPS data) and other times, this becomes a problem. Almost all images have meta-data fields.

a6k Loc: Detroit & Sanibel

The claim is that EXIFTOOL does not change the image. If you make a careful observation of the file size before and after you should be able to get a credible answer. Other programs may not have the same safety built in. I found that even EXIFTOOL could not change the metadata in my raw files but some programs store changes to the file in a "side car" file so that is worth consideration.

CHG_CANON Loc: the Windy City

Editing the metadata of an image file doesn't impact the quality of the JPEG image data, although the tool you use should be confirmed to assure it doesn't recompress the JPEG. This post provides a detailed method to confirm:

https://photo.stackexchange.com/questions/69223/does-writing-exif-tags-influence-jpeg-quality

Joe Blow

Before changing to RAW, which I highly recommend, I saved my JPGs in an event folder. In that event folder I added a subfolder which held all my processed photos. I never opened and closed a photo in the event folder. I would copy the photo into my editor and saved that into the subfolder. The original JPG remained the same as when it was d/l.

I do recommend you try using RAW.

rmalarz Loc: Tempe, Arizona

Observing the file size change will not necessarily indicate a change to the image.
--Bob

rmalarz Loc: Tempe, Arizona

All of my images, film and digital, have exif data. I strip that data prior to posting in order to avoid misleading those certain folks who feel it's necessary to view that information.
-Bob

kd7eir Loc: Tucson, AZ

Let's throw some facts in here before too many people throw their "opinion" in here -

Absolutely not. You need to edit the file and re-save it as a JPEG in order to compound the effects of image compression. Just viewing it has no effect at all — if it did, all of the JPEGs on the web would "wear out" completely in a day or two at most. Google would need to apply fresh coats of "paint" every couple of seconds on their search results page if opening a JPEG degraded it.

Lossy compression happens only when the file is saved. This is the part that causes loss of quality. However, just closing the file is not enough to trigger lossy compression: you have to save it.

"Lossy decompression" never happens. There's no such thing. There can't be, because the data that got thrown out during the lossy compression phase is gone. If you could somehow reconstruct it, then you'd have a lossless compression algorithm, not a lossy one.

The meta data is separate from the image data of the same file. One does not affect the other. The meta data in the image file is not even compressed, it is pretty much plain raw ASCII data, just in defined areas of the hex of the file. That is why you can easily view the meta data. It is not encrypted or compressed.


For the non-believers I can delve into graduate-level math and physics to prove my point, but knowledge of quantization, the fact that functions can be decomposed into sums of sines and cosines of various frequencies, and the fact that Fourier series come in many flavors, particularly Fourier
Cosine Series: Any reasonable function f (t) defined on [0, π] can
be well-approximated as a sum of cosines,
f (t) ≈ a0
+ a1 cos(t)
+ a2 cos(2t)
+ · · ·
+ aN cos(Nt)
if we pick the ak correctly (and take N large enough).

before you would likely be able to glean any understanding from it.

ELNikkor

my jpegs are all I have of most of mine since 2005, and they still look great and print to 11x just fine...