charles tabb Loc: Richmond VA.

I think this has been answered before but I can't remember.

If I open a jpeg file and then close it is there any loss?

If so, is the loss naggable?

Ysarex Loc: St. Louis

No loss.

Further loss to a JPEG results if the file is opened and edited and then re-saved as a JPEG.
Loss is caused primarily by editing (changes to tone/color) and secondarily by re-compression when re-saved.

charles tabb Loc: Richmond VA.

Thanks for your answer.
I felt that what the sales person on B&H was wrong.
He just didn't explain it like you have.

BebuLamar

If you open and then save there is lost, you don't have to make any change just save it. If you open and simply close it there is no lost.

CHG_CANON Loc: the Windy City

Absolutely no loss.

The single greatest 'loss' of a JPEG is when the file is initially created, converting the bit-depth from a typically 12-bit (or higher) from the image sensor into an 8-bit JPEG.

What is 12-bit you might ask? That's 2^12 aka 2 to the power of 12 = 4096. An 8-bit JPEG has 256 tones of each of the three color channels of data (Red, Green, Blue aka RGB). These three RGB color channels work in combination to produce a much subtler, wider range of tones between total black and total white. A 12-bit file can combine RGB into more discrete shades, 4096 specifically for each individual RGB color channel.

When the JPEG is created, that 'shading' of the 12-bit image is mapped to the exact 8-bit color, or the nearest 8-bit value. The human eye can't see all the possible colors of an 8-bit file, so this isn't something you'd notice. The bit-depth enables you to better edit your images, where that wider possible tonal range avoids 'gaps' in the colors, something you can occasional encounter in the blue skies of JPEGs, where the transitions of shades of blue are uneven.

Opening and closing a JPEG does nothing to the contents of the file. Copying / moving the files does nothing to the contents of the file. Only when you 're-fire' the JPEG compression engine to save an edited version of the JPEG does the contents of the JPEG change, possibly. The bit-depth remains the same at 8-bit, so there isn't color data being tossed like the 12-bit to 8-bit conversion. If you change / lower the JPEG quality, only then is more data removed.

We hear about JPEG being a lossy compression. That JPEG 'quality' setting is the lossy compression. Again, that loss occurs when the new image file is created via a digital editor. Opening the file 'inflates' the compressed JPEG as stored in disk. The file doesn't change, viewing the JPEG is simply the software reading the data and 'inflating' the compressed data to display the contents, just like if you unfolded a letter from inside an envelope.

Changing the JPEG quality and saving a new version of the image is like cutting some pieces out of the letter you unfolded. If you cut on the edges, margins of the letter, and the file is smaller but no visual difference to the letter content. Using a still lower quality (say less than 80%) might involve cutting some content, a word or sentence here and there. Maybe it will make a visual difference, maybe not. But, once the trimmed letter is folded back into the envelop, it doesn't change simply from opening and closing over and over again.

Ysarex Loc: St. Louis

That's correct. Re-compression will cause harm regardless of editing changes made or not. But there's no point to re-save the file if you don't make a change.

This is worth further comment because it's a common misunderstanding that the loss due to re-compression is why cautions exist concerning editing JPEGs. The re-compression loss is negligible. The loss due to consequential edits of tone/color is typically far more severe.

The whole concern grows increasingly moot with newer cameras of higher resolution. The degradation due to editing and re-compression is swamped in the resolution of a 24mp file and we can't see it.

larryepage Loc: North Texas area

If your camera allows you to select the resolution and level of initial compression, you can save a lot of headache by making wise choices. When memory was expensive and capacity was limited, many folks got in the habit of saving limited resolution images with very high levels of compression. There is rarely a physical reason to need to do that today. If you save your images with maximum available resolution and the minimal level of compression, you will have a much stronger starting point and will limit later losses. Your camera manual should explain how to do this.

DirtFarmer Loc: Escaped from the NYC area, back to MA

Study of multiple writes of jpgs

Extract from abstract of study:
"This study shows that much, if not most, of the degradation occurs in the first writing of the jpg file. The degree of degradation, as expected, will depend on the “quality factor” specified in the program doing the rewriting, since that determines the degree of lossy compression. However, instead of finding the image degradation continuing unabated as long as the rewrites continue, the degree of degradation saturates at some point. In other words, the image degradation will increase with rewrites to a point, after which there will be no further degradation. That point will depend on the “quality factor” used for the rewrites."

bsprague Loc: Lacey, WA, USA

However, theory and reality don't always match.

The theory is that each time you open a JPEG and then "Save" or "Save As" the JPEG codec does it's work and looks for extra data to shed. Apparently that used to be potentially severe.

JPEG standards have improved and those "saves" don't do much damage.

Make a copy of a favorite JPEG and see how many times you can save it before you see noticeable damage.

charles tabb Loc: Richmond VA.

Thank you ever so much SIR.

Longshadow Loc: Audubon, PA, United States

Simply viewing changes nothing.

dpullum Loc: Tampa Florida

And! If small changes happen for whatever quirk, can we see it on viewing by monitor or large screen TV, and if printed, is the printer going make that small change significant, and if so, can our eye/mind perceive the difference?

Architect1776 Loc: In my mind

Your question has been answered.
Another thought is once you have processed the photo how many times really does it get reprocessed?
Then if reprocessed again realistically how many times will that be done?
Bottom line is that for most people it is a one and done so this continuous reprocessing is more of a theoretical discussion than a real world issue.
Most of us would never see degradation even after several open and saves after reprocessing if that were ever done.
So don't worry about opening and closing JPEGs.

jlg1000 Loc: Uruguay / South America

No
Nein
Нет
Nes pa

camerapapi Loc: Miami, Fl.

I am in agreement with Mr. Sprague. Modern JPEG files are not the files of a few years ago. Modern JPEG files have excellent quality and if you have to make any adjustments to them keep them simple or better yet, leave the file like it is.
Opening and closing a JPEG, as has already been said, causes no damage to the file.