DanCulleton

Think of JPEGs as an output format ONLY!

John_F Loc: Minneapolis, MN

Speaking of bit depth, are we talking about per color channel (RGB) or overall. At 8 bits per color channel, a 6000 by 4000 pixel image will be a 72 Megabyte file, exclusive of file header bytes.

Mr palmer Loc: Currently: Colorado, USA, Terra, Sol

Ok. Please check my methodology. I grabbed a JPG that was SOOC. Distant branches, plenty of stone and texture in the middle. Opened it with PSCC and saved it under another name (2nd generation). Then opened the second generation and saved it as a third generation name. I continued until I had original and 9 generations.
I saved 2 sets, one that was saved at PS Level 12 (maximum), and another set that was saved at Level 10 (from an old chat with a pro lab. Miller's or Whcc, I don't remember, maybe Burrell) - which is High, but much smaller file size (which the lab preferred).

So, I have the Original image SOOC, a 9th generation saved as Jpg level 12 from Photoshop, and a 9th generation saved as Jpg level 10 from Photoshop.

What do you all think? Is my methodology ok? Specify improvements as needed. Also, can I post full size images on UHH or do I need to link to somewhere?

Walt

Wasabi

Todd,


As I now understand it the original statement meant to save with another jpeg compression, not merely to 'save' the file. There are programs that allow you to view and 'save' without re-compressing the file. I agree the subsequent compression would be more likely to introduce changes.

Mr palmer Loc: Currently: Colorado, USA, Terra, Sol

Here are my results:
https://www.dropbox.com/sh/acddxfr153wvnzi/AAAZKc-4maGk6d8vyMlh4Zxza?dl=0

Kuzano

It occurs to me that the simplest method of explaining when compression of a JPEG takes place is to note that ONLY two commands related to JPEG files cause the compression algorythm to run.

1) File > Save
2) File > Save as.

No other command runs compression on a JPEG file.

The format JPEG is an acronym for the group who created it.... Joint Photographic Experts Group.

It also occurs to me that using the term "decompress" is a misnomer regarding JPEG files. That name is an implication that there is data in a JPEG file that comes back into play when one opens the file. I do not think that is true. The Compression Algorythm discards (throws out) data at whatever quality level is chosen. That data is gone... never to come back into play on files that have been compressed. It's not like a video or autdio file that is compressed and decompressed for saving space and for play.

JPEG does not require a CODEC.... Compress/Decompress to view. But using Save or Saves DOES run the compression algorythm again. Using the term decompression does imply that the discarded data comes back into play. Not so... the discarded data is never available again, other than from a file prior to an edit and Save.

I have used TIFF format, and TIF (tagged information format) is somewhat more complex than JPEG and much bigger in file size. There are many variants of TIF/TIFF.

The only time I really found TIFF easy to us, is that I have owned camera's that record/output RAW, JPEG and TIFF. Those camera's were my Olympus E1 Professional, and Fujifilm S(x)Pro camera's.

We can look to the camera manufacturers for the incredibly confusing understandings of both JPEG and lack of TIFF in a consistent/available option in our equipment.

Quaking Aspen Loc: Cottage Grove, OR

One of my professions before I retired was application programming for a portrait studio company. It has been 10 years since I retired from the job, so I may mis-remember but I remember being able to choose the level of lossiness when manipulating jpeg files, anywhere from no loss to fairly highly compressed. We generally used a no-loss format for general manipulation of the files so there wouldn't be any degradation in the image. If we needed to absolutely guarantee that an image file would not be altered we would generally use *.bmp format which creates a large file but keeps all the image data (but isn't the same thing as RAW).

I don't know current image manipulation software or its capabilities, and I'm sure things have changed a lot in 10 years.

Also, TIFF is, strictly speaking, a storage format and not an image format. It was used in fax imaging among other uses, but could be used to store pretty much any kind of file.

Just my 2cents worth.

DaveC1 Loc: South East US

I tend to to this with all image files. So my original file is say img0001.tif (or .jpg or whatever) my modification is saved as img0001r1.1.tif if I move to a different type of modification the saved file is img0001r2.1.tif so there is a trail of my work.

shelty Loc: Medford, OR

I'm glad someone got it right.

terry44 Loc: Tuolumne County California, Maui Hawaii

I have only used raw since I discovered it years ago for that very reason one thing I wonder does just making a copy of a jpg to work on degrade the original I am pretty sure that flipping/rotating, and cropping probably does not degrade it, at least to anything that will be noticeable.

Bobspez Loc: Southern NJ, USA

A picture (or two) is worth a thousand words. To my eye, the change may have been to the better. I detect slightly better contrast with the jpg below that was edited and saved 11 times in Windows paint, after adding a colored number from 1 to 10 below the "17".

Original jpg

(Download)

jpg edited and saved 11 times in Microsoft Paint

(Download)

Kuzano

Since I rely on my images for income, I never shoot RAW!

SOOC, from a custom profile or a properly adjusted camera is where the money is!

JPEG only, with minimal PP!

shelty Loc: Medford, OR

It may work for that, but you do get a loss of picture quality though. I have a camera that only shoots in jpeg. So if I want to do some work on one of the images, I save it in PSD first.

rmalarz Loc: Tempe, Arizona

GENorkus, that's what I do with a number of photos I've downloaded from here, with permission, in order to edit them further. Open>Save as .tif> Close. Open the tif file and edit that. Then, save as jpg to repost. It's definitely not at good as working with the RAW file, but for a quick illustration of a point, it works reasonably well.
--Bob

Mr palmer Loc: Currently: Colorado, USA, Terra, Sol

Just know that I am right; whatever I think. At least I'm not wrong; whatever that means.
And Raws are like negatives, if you want to go back and process that Tri-X negative to bring out the subtle color you remember, I always reprocess it in E-6 chemicals. [Rant off]