Data transfer: Images degrading...any ideas?

I have something that i've been noticing little by little. About a year ago, before I made the PC to Mac switch, I bought an external USB drive and backed up all my data. I formatted the drive in FAT32, knowing i'd probably be switching to a Mac sometime after.

Fast forward...i've been noticing that a number of my pictures have some very noticeable degradation and pixelation. I'd like to know where in the process this happened, but it's tough, as a lot of these are digital camera pics from family events and stuff that I don't look at very often.

I guess it could be from the following:
-Transferring from the PC to the external drive.
-Transferring from the PC to the Mac.
-Moving the Data around within the drive(s) to organize it.
-Defragmenting the drive when I was using it with the PC.
-Something else.

Any ideas on how this can happen, and how I can avoid it in the future? I plan on replacing the HD in my Macbook, and i'm afraid that i'll have files degrading that I won't be able to replace.

-Nick

Isn't FAT32 limiting file sizes to 4MB or less? Maybe the images were compressed somehow to fit? Dunno never heard of this. That was just a logical guess.

Maybe a workaround would have been compressing each image before storing them on the drive? Would have been a painstaking procedure though...

MacHeadCase said:

Isn't FAT32 limiting file sizes to 4MB or less?

Click to expand...

4GB is the size limit on FAT32

DOH! Neeeeever mind...

There goes my theory.

Second theory...

The only thing I can think of is that the number of pixels per square inch in certain images is not high enough. Are all the images pixellated or are only a few of them bad? If you have Photoshop you could easily verify this with the Image Size thingy.

it's definately not caused by moving/copying data. os copy code does a perfect bit for bit copy otherwise the file would be corrupt and you couldnt open it.

MacHeadCase said:

Second theory...

The only thing I can think of is that the number of pixels per square inch in certain images is not high enough. Are all the images pixellated or are only a few of them bad? If you have Photoshop you could easily verify this with the Image Size thingy.

Click to expand...

It's only some images. I have Photoshop...what image size thingy are you referring to?

hartrick said:

it's definately not caused by moving/copying data. os copy code does a perfect bit for bit copy otherwise the file would be corrupt and you couldnt open it.

Click to expand...

Hmm. Do you think this could've been cause by defragging?

Also, i'm not sure sure it's a bit for bit copy. Whenever I copy folders, it's never the EXACT same size. There's always some variation. Maybe not large, but if you look in the information window under the size listed in bytes, there's usually a difference.

BTW, Thanks for the replies guys.

-Nick

I have CS2 and I can see the number of pixels per inch by typing Command + Option + I. See screenie below...

When you see 72ppi (pixels per inch) for an image, that is a screen/monitor resolution and when you print the image, it comes out looking pixellated. That rez is ok for all multimedia work i.e. webpages, CD/DVD presentation, etc. but if you go and print the same image, keeping the same rez, it looks bad.

The example I have as an attachment to this post would print ok and would not be pixellated because I have a higher rez for the printing process. For printing with an inkjet printer 150ppi and above is good.

what are you using to open / View the files?

The images should not degrade if all you are doing is opening and copying them. However, if you open and save then you start loosing quality. Every time the image is re-compressed (saved), the algorithms could be misinterpreted, thus quality will be loose, this is why Aperture and Lightroom use non-destructive editing concepts or why the professionals use uncompressed formats like RAW or TIFF.

hartrick said:

it's definately not caused by moving/copying data. os copy code does a perfect bit for bit copy otherwise the file would be corrupt and you couldnt open it.

Click to expand...

This, is absolutely correct. Also, you cannot necessarily trust whichever tool of the OS (Get Info, ls -l, etc.) to tell you the exact number of bytes in any given file. You can, however, trust that anything that straight up copies a file (Finder drag 'n drop, UNIX cp, mv, etc.) and backup programs will make a bit for bit exact replica of the original file to the target media. If this were not the case, any executable program would be immediately corrupted and no longer executable, or worse executable but with unpredictable errors.

Most operating systems (Mac OS included) perform continual copy operations, file moves, memory page-outs and the like in the background without intervention, shuffling gigs of data around per month with flawless accuracy. Believe me, if something were to go wrong there, you'd know it pretty darn quick as the system would fall ill, and eventually be unbootable/unusable.

Now, compression of images is a whole different issue. Copying one jpg file from one media to another isn't going to do anything to the image quality, as everything is replicated bit for bit, compression and all.

It is the compression that is the bug-a-boo of image quality. Every time you load a .jpg image into an image editor and save it, even with the same quality level of compression it is going to get irreversibly compressed a little bit more. The only time this does not happen is if you load the file, say, from the camera on which it was taken and save it in a non-compressed format. Non compressed formats are like .tiff or Photoshop's .PSD format.

This is why when I take pictures off of my digital camera, any picture that I load up to work on with Photoshop is subsequently saved in native .PSD format, regardless of how much bigger it makes the file. Only if I need it to be compressed for the usual reasons (emailing, posting on a web site, etc.) will I save to .jpg, and I do not consider the resultant jpeg to be anything but a disposable one-off version of the image. Images in .psd format can be reloaded and edited with no loss in image quality as long as they are not saved in a lossy compressed form.

So anyway, to conclude. What has probably happened is the mechanism you've used over time to shuffle these image files around has introduced additional, even if minute, compression artifacts. Standard operating system copy utilities will not, and cannot introduce compression to files of any type, image or no.

And yes compressed image formats like .jpg and .gif will degrade the quality of your images if you keep saving them in the same file format. Use lossless file formats as was posted above. I had forgotten about that possibility as well.

I always save a copy of my RAW files in either .tif or .psd.