file quality

[koko]

maybe my question sounds silly , but frequently comes
to mind.
If I scanned a photo and have kept in a tiff or
gif format... Has passed time and has then kept file on floppy,
Then through time on cd, has then copied on C: and then
copied on D: and so on and on.
Question: whether quality of file falls, or it is kept
100 %. in a case when
file opens and visually do not notice falling of
quality.
:(

[Paul Komski]

Generally speaking a file is usually OK when it is copied but, for a number of reasons, can become corrupted during the process or at a later date if the media on which it is stored becomes damaged or altered.

Thus, files will generally either work or not; mostly an all or none phenomenon. Whether they are graphics files, or not, what you won't see is a gradual deterioration of the picture quality over time in a way that can (and usually does) happen to ordinary photographs and which is a chemical process.

[gwallen4]

Tiff image saves can be uncompressed (lossless) or compressed (subject to some loss of definition). Everytime you open (in an imaging program) and save a file in the compressed tiff mode, it will further degrade the image. Uncompressed tiff images theoretically could be opened and resaved as many times as desired without any loss although I prefer the bmp format for lossless uncompressed saves.

Images saved in any format (tiff, gif, bmp, jpg etc.) can be copied to a different storage medium (hard drive, floppy, CD-R) without any loss at all and will remain essentially intact for the life of the media.

The life of floppies is very limited and I would not depend on saving an image on floppy for more than a few months. CD-R is much better, maybe as long as 20 years or more.

I prefer the bmp format for uncompressed image files. There is no compression with the bmp format so I can open, manipulate and save the image as often as I want with no loss. However bmp (and tiff) uncompressed files can be very large, 9 MB for a typical picture taken with a 3 megapixel camera. So for saving large numbers of pictures I usually use the jpg format with about 1 to 10 compression so the pictures are only 1 MB but barely have any observable loss of resolution. More compression can be used if you plan on distributing images over the Internet, but this involves more loss.

[mjc]

Openning a file, by itself, does not have an impact on the quality. It is the saving the file that change or alter the quality.

[sleddog]

Originally posted by gwallen4
Tiff image saves can be uncompressed (lossless) or compressed (subject to some loss of definition). Everytime you open (in an imaging program) and save a file in the compressed tiff mode, it will further degrade the image.

Umm, I don't think so. TIFF images are usually compressed using either RLE (run length encoding) or LZW (Lempel-Ziv-Welch). Both are lossless compression schemes.

What you say is true of the JPEG format. Repeatedly saving a jpeg image will cause it to deteriorate. Though I've found that repeatedly saving a file using exactly the same compression ratio causes minimal deterioration. If you change the ratio each time you save the file then quality suffers much more.

And TIFF is a recognized, cross-platform image format. BMP is a MS Windows thing. A TIFF image may be save with CMYK colour information for prepress. BMP is limited to RGB color information.

[gwallen4]

Sleddog,

You are absolutely correct on tif images being lossless. Thanks for the correction.

[kayofcircles]

Agree with tiff format being best for pics from one puter to next, and also that they're lossless. Do think you're partially right, though, gwallen4 because a friend was using a ULead program that made tiffs with no compression whatsoever. File size on tiff same as bmp files...so no real advantage to a tiff over a bmp file because Ulead didn't do layering well anyway. I use the PSP format..similar to tiff..for everything until ready to jpeg or share. No loss..and "save" every few minutes after one experience where I had worked for hours on a pic, and then got an error message..and lost everything. Now hit the Control S every few minutes! :D

Old lady fuss...I HATE jpgs and bad digitals..and my uncle sends me a combo of the two...WAIL...:(

[sleddog]

Yes. To be clear, TIFFs may be compressed or uncompressed, as gwallen4 originally stated. What I said above was applicable to compressed TIFFs. An uncompressed TIFF will indeed be about the same filesize as a BMP.

TIFFs, like many image formats, do not support layers. The PSP format does support layers, but is a proprietary format used by Paint Shop Pro on Windows. I'm not knocking it; it's great. But don't send one to a commercial printer for the cover of your newsletter :) For a purpose like that a TIFF saved with CMYK colour information is best, as it can be read and outputted by just about any hardware/software.

All the different image formats have strengths and weaknesses. It's just a matter of selecting the appropriate format for the job at hand.