Wednesday, April 04, 2007

JPEG files lose detail each time altered

From: John
DearMYRTLE
Responding to the following quoted column "READERS' FEEDBACK: Different Family Lines"


From: larcher kathryn
[...] By the way, it's best to scan photos in TIFF format since JPEG compresses the file thus losing information EACH TIME the file is opened. Then make a JEPG copy if you want to send by email or put on a website. Best only to scan a photo once (or twice) since each time exposes it to a lot of very bright light.

DearKATHRYN
Good points! Ol' Myrt uses TIFF for important photos and GIF for most other photos quite simply because of file size. While .jpg sounds good for exchanging photos, they really do become corrupted over time and look less marvelous. However, with the noses on some of Myrt's ancestors it wouldn't make any difference![...]"
MYRT, not sure if I'm miss-interpreting you (and/or your original contributor) but if I am not, I'm afraid you are doing a bit of a miss-service here and unnecessarily alarming less tech-savvy genealogists about the state of their digital picture collections by promoting this FALLACY!

BACKGROUND FACT: JPEG/JPG is a "lossy" file compression format. It does discard pixels as it SAVES in order to create a smaller file size. So, if one has a great super-resolution, highly-detailed scan of an antique photo originally saved directly from the scan process in "raw" format such as TIF/TIFF (which would likely be an enormous multi-megabyte-sized file on one's disk) and then opens that file and saves it (or hopefully a copy and not "it") in the JPEG format, this resulting second saved photo file (JPEG copy), will be much smaller on disk, AND WILL HAVE LOST A GREAT DEAL OF PIXELS AND THUS QUITE LIKELY A GREAT DEAL OF DETAIL TOO from it's original TIF/TIFF version.


This everyone should make themselves aware of. So if you want to scan-to-preserve an antique (or any photo) then save it in the highest resolution your system can handle and in the raw format of TIF/TIFF, but if you then want to email a copy just to show it, do save a COPY of that TIF/TIFF format file in the JPEG format to reduce it's enormous size, BUT DON'T REPLACE YOUR OWN ORIGINAL HIGH QUALITY SCAN with that copy (you should end up with two versions, the large file high-quality, and the small file compressed.) This way, one has the great high detail for archiving and future printing, and one also has the smaller "snapshot" of the image for sharing via email, etc.

(The FALLACY is a misinterpretation of this)
FACT: Simply opening, and CLOSING, a JPEG format image DOES NOT CAUSE FURTHER DETERIORATION! The image does not deteriorate over time by simply looking at it!

(With this) FACT: If you open the image, and make any sort of change to it, no matter how slight (cropping, sizing, etc.), and then SAVE these changes, it is at that point that the compression format of the JPEG would essentially start anew and so compress and discard pixels based on this starting point (of an image which had already lost pixels and details from it's original TIFF format, at it's first "save-as" in JPEG format)

My research also tells me that OPENING, and SAVING, WITHOUT CHANGING ANYTHING, also DOES NOT cause deterioration to the image, however, since it's so easy to mouse-click, one could accidentally change something so slight as to not be noticeable, but which could cause the Jpeg compression process to kick-in again and begin to discard more pixels. And furthermore, file COPYING, as in copying the file from folder to folder, or drive to drive, also has absolutely ZERO effect on the file and/or the image contained in that file! Anymore than when copying a Doc format file to a disk would make any changes to it!

After reading your email, I did a search and was truly surprised to realize how many innocent folks have misinterpreted this important difference. Because of that misconception, I can hear the email servers choking and dying due to being clogged by massive and unnecessarily huge TIFF files of Junior's latest birthday party being sent around the Internet!

A research effort at photo technology information sites (not just user shared info) should back me up in this important distinction.

DearJOHN,
THANK-YOU, thank-you to you and several other readers who studied this column, and noted that my words "corrupted over time" about .JPG files were not clear, thereby promoting an erroneous conclusion. This is why it is so important to share back and forth, to keep us on the right track. I appreciate your detailed response in making this distinction for Ol' Myrt and her readers.

There can even be subtle changes to .JPEG we are sometimes not aware of making because it happens when one is NOT using the photo-editing software that came with one's digital camera:

WINDOWS RESIZE BEFORE EMAILING: Since most email programs limit file size on email attachments, the use of .JPEG might sound good, since the files are much smaller. When looking at a folder of picture files in Windows, if one clicks on a specific picture file and selects sending it via email, there is a screen that comes up where one must decide about file size before sending. The default in Windows XP is to make the file smaller. For a .JPEG file this would also mean a change in clarity. The new Windows Vista provides a drop-down menu to specify file size before emailing and it isn't obvious whether or not one is changing the .JPEG picture from its original file size.

Genealogists do tend to share picture files with other genealogists via email rather than snail mail.

So Ol' Myrt saves her better pictures in the larger file size .TIFF format, and others in .GIF file format -- particularly those I plan to email to a distant cousin.

Happy family tree climbing!
Myrt :)
DearMYRTLE,
Your friend in genealogy.
Myrt@DearMYRTLE.com
www.DearMYRTLE.com

(c) 2007 All Rights Reserved.

No comments:

Post a Comment