JPG files deteriorating?

[Mick]

A friend mentioned to me that he had heard that every time you open a JPG file on a computer and close it again you actually lose some file integrity so that with time your image will deteriorate. I have never heard of anything like this before and frankly it makes absolutely no sense to me since a digital file should remain exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[Jon31687]

Here's the situation: you can open & close a JPEG however many times you want, and it will not affect the quality of the digitally stored file.

However, if you SAVE the file, rather than close it, except in cases where you specify 0% compression and 0% smoothing, you will get a loss of quality (imaging software typically sets compression to 10-20% on and JPEG save, thus shrinking the file size at the expense of quality. Thus if you say 'save changes' each time you close a Jpeg, without specifying no compression, you are 'deteriorating' the image quality. Hope that helps answer the question.

Cheers,

-Jon

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[Pepe]

This is not true. If you open a JPEG file to be displayed and NOT modify and you CLOSE it, nothing happens to the JPEG file. However, if you SAVE it - even if you did not modify it - it degrades the image.

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[Leon Wittwer]

The degradation on saving a jpg image depends strongly on the amount of compression. I typically use the maximum quality, minimum compression in photoshop to store my shots. This provides compressions ranging from 4 to 8 in file size. At this level of compression, you can open and save (recompress) many times without significant degradation. I once took a shot with a lot of detail through ten cycles and the tenth version was very little changed from the first. What change there were occurred during the first cycle. The remaining nine cycles were almost lossless. I did the test using the difference channel in photoshop to quantify the pixel for pixel differences at each cycle of compression/decompression. At higher compressions, the degradation increases. At low quality, it don't take long to get significant degradation.

Cheers,

-Jon

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[arjuna]

seeing a few replies that seem odd, gotta add my two cents...

JPG is a lossy form of compression, if you save a JPG as a JPG you will loose information...

if you are going to mess with a picture i think it's best to convert it to either a 'raw' format (like TIFF) or a lossless compression format like GIF or BMP, those you can save over and over again with no loss...

some people comment that they don't notice loss repeatedly saving a JPG file, and while it is possible to miniize the loss, you are 'walking the razors edge' so to speak, much better to convert the pic to a lossles format...also there is a question of file-size vs screen-size...if the image is shrunk by 200% so that you can fit the whole thing on your screen you obviously aren't going to see all the loss happening...

anyhow, my $.o2...

 

[Paul Pashby]

seeing a few replies that seem odd, gotta add my two cents...

JPG is a lossy form of compression, if you save a JPG as a JPG you
will loose information...

if you are going to mess with a picture i think it's best to
convert it to either a 'raw' format (like TIFF) or a lossless
compression format like GIF or BMP, those you can save over and
over again with no loss...

some people comment that they don't notice loss repeatedly saving a
JPG file, and while it is possible to miniize the loss, you are
'walking the razors edge' so to speak, much better to convert the
pic to a lossles format...also there is a question of file-size vs
screen-size...if the image is shrunk by 200% so that you can fit
the whole thing on your screen you obviously aren't going to see
all the loss happening...

anyhow, my $.o2...

Maybe I misunderstand your post, but I don't believe that differing JPEG compression levels have any affect on the underlying resolution of the original image. To be sure, the sharpness of more heavily compressed images may suffer, but not the size.

 

[khilst]

Does copying the file from one drive to another also coss the loss.

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[Leon Wittwer]

No, the loss comes from uncompressing, recompressing and rewriting the file. File copies do not uncompress or otherwise change the file.

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[arjuna]

the pixel number won't change, of course not...you DO loose information tho, the sharpness is dulled, the colors are slowely being removed...what to use as an example...

you take a piece of paper with writing all over it, perhaps small letters or an intricate picture...in order to fit it into your pocket you fold it several times (you might correlate the number of times you fold the paper to the compression setting you use on the JPG, the higher the ratio to more you fold it)...now you have all these creases through the page when you unfold it to look at it...after folding and unfolding several times the ink and paper wears down, leaves you with usless or unreadable scribbles eventualy...

that analogy a little off because looking at a JPG does nothing to it, it's the opening in an editor and saving again that 'wears it down'...is this something you want to do to your pics?...

Maybe I misunderstand your post, but I don't believe that differing
JPEG compression levels have any affect on the underlying
resolution of the original image. To be sure, the sharpness of more
heavily compressed images may suffer, but not the size.

 

[Dan Clark]

I'm curious, you mentioned using PhotoShop. I understand that its native format is lossless. Why not save it in it's native format?

This brings me to the issue of workflow - from opening a new image file for the first time to manipulating in editing software to printing/publishing/archiving it. While I'm a fairly experienced photographer, I'm relatively new at digital photography and image editing. I'm trying to understand the how different people manage workflow. What are the basic steps?

Thanks and regards,

Dan.

Cheers,

-Jon

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[Jon31687]

Hi Dan,

The only reason not to save it as a bitmap/photoshop uncompressed (i.e. lossless) image is the size of the files. Typically, a jpeg is far smaller than an uncompressed file (which is why your typical 3MP digicam image stores at either 1000K as a low-compression JPEG, 300K as a moderate compression JPEG, or 8000K uncompressed/TIFF). So if you have 256MB RAM in your computer, and a few gigs of free hard drive space (or a CD-RW), using a lossless format would certainly be better for image quality (if you plan on doing a lot of manipulation, that is).

Good luck,

-Jon

This brings me to the issue of workflow - from opening a new image
file for the first time to manipulating in editing software to
printing/publishing/archiving it. While I'm a fairly experienced
photographer, I'm relatively new at digital photography and image
editing. I'm trying to understand the how different people manage
workflow. What are the basic steps?

Thanks and regards,

Dan.

Cheers,

-Jon

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[arjuna]

there is a difference between a 'raw' format (uncompressed, such as a TIFF) that would be the full 8000K pic you're describing and a BMP or GIF file which does use compression, just a lossless form of compression (think of a ZIP file for programs for instance, you unzip it and it's all there)...the problem with JPG is the loss, the nice part is the size...

Hi Dan,

The only reason not to save it as a bitmap/photoshop uncompressed
(i.e. lossless) image is the size of the files. Typically, a jpeg
is far smaller than an uncompressed file (which is why your typical
3MP digicam image stores at either 1000K as a low-compression JPEG,
300K as a moderate compression JPEG, or 8000K uncompressed/TIFF).
So if you have 256MB RAM in your computer, and a few gigs of free
hard drive space (or a CD-RW), using a lossless format would
certainly be better for image quality (if you plan on doing a lot
of manipulation, that is).

Good luck,

-Jon

 

[Leon Wittwer]

Dan, You are right regarding Photoshop's native format and I use it when I am working on a picture. My jpg tests were motivated by two considerations. The first was just curiousity. I wanted to find out what compression level resulted in what level of degradation. The second was more practical. It is not unusual to want to go back and rework some portion of an image some time after I thought I had finished it. I wanted to know what level of compression, if any, was "near" lossless so I could rework a number of times without significant image degradation.

This brings me to the issue of workflow - from opening a new image
file for the first time to manipulating in editing software to
printing/publishing/archiving it. While I'm a fairly experienced
photographer, I'm relatively new at digital photography and image
editing. I'm trying to understand the how different people manage
workflow. What are the basic steps?

Thanks and regards,

Dan.

Cheers,

-Jon

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???

 

[Dan Clark]

Jon,

Fortunately, I have 512Mb RAM, several gigs of free disk space and a CD-RW. I used to think that I had a hot computer. Now, I think that it is nice, but not extraordinary. This is becoming more the norm these days.

And, I like to manipulate the images. Lot's of fun! For me, the PSD format seems to be the best. But, I'm still a student of the art. Still learnin'. If someone else has a better method or process, I'll happily switch.

Regards,

Dan.

The only reason not to save it as a bitmap/photoshop uncompressed
(i.e. lossless) image is the size of the files. Typically, a jpeg
is far smaller than an uncompressed file (which is why your typical
3MP digicam image stores at either 1000K as a low-compression JPEG,
300K as a moderate compression JPEG, or 8000K uncompressed/TIFF).
So if you have 256MB RAM in your computer, and a few gigs of free
hard drive space (or a CD-RW), using a lossless format would
certainly be better for image quality (if you plan on doing a lot
of manipulation, that is).

Good luck,

-Jon

This brings me to the issue of workflow - from opening a new image
file for the first time to manipulating in editing software to
printing/publishing/archiving it. While I'm a fairly experienced
photographer, I'm relatively new at digital photography and image
editing. I'm trying to understand the how different people manage
workflow. What are the basic steps?

Thanks and regards,

Dan.

Cheers,

-Jon

A friend mentioned to me that he had heard that every time you open
a JPG file on a computer and close it again you actually lose some
file integrity so that with time your image will deteriorate. I
have never heard of anything like this before and frankly it makes
absolutely no sense to me since a digital file should remain
exactly the same unless it has been edited.

Can amyone out there shed a litle light on this myth/truth???