TIFF Compression

[OviV]

Is is safe to use LZW compression on my TIFF files? Will I lose anything like in JPGs?

Thanks,
Ovi

[fwhitesides]

LZW compression is touted as lossless. However, I was wondering the same thing as you.

Is there any reason why we should not store a TIFF in LZW compression? Also, is there really a difference between PC and Macintosh byte order?

[robertwgross]

I can speak to that a little. Back in the old days, there were two forms of TIF. There was standard TIF and then there was TIF-LZW. In those old days, one limitation of graphics speed was the main processor. We could do the TIF-LZW compression, but it took quite few machine cycles to crunch it or uncrunch it, so it took time. For some arbitrary image file, it might take five seconds to save a TIF, but it took 10 seconds to save a TIF-LZW.

The other limitation was disk space. Hard disks used to cost a lot of money in the old days, so if a TIF file took up 2MB and the TIF-LZW file took up 1.5MB, then which one would you want to save? A side effect of that 0.5MB of disk saved was that the file might save quicker than it would have at 2.0MB. So, sometimes the net effect of TIF-LZW was a little speed and a little disk space.

TIF-LZW worked pretty well if the image was very compressible. By that, I mean that there was a lot of plain color with little detail. As we started moving into more and more complex images, the savings of TIF-LZW became less and less. There are some graphics programs that do not support TIF-LZW, but everything supports plain TIF.

Now we have both fast processors and virtually unlimited and cheap disk space, so TIF-LZW is not quite as relevant now as it used to be.

---Bob Gross---

[OviV]

Main reason I am asking is for the sake of archiving my images to CDRW(only holds 650MB). Some of my shooting for one day will exceed that if I add my TIFFs to the archive. Maybe I should only archive the RAW images. What do you guys think?

Ovi

[robertwgross]

TIF-LZW is a lossless format. TIF is also, but the bits are not packed as efficiently as with TIF-LZW. Repeated saving will not cause degradation.

JPEG is a lossy format. With some programs, you can select the degree of loss so that the image is anywhere from awful to almost-perfect. A JPEG saved in almost-perfect quality is virtually perfect to the naked eye or in a normal print. It is, however, not "perfect", and repeated trials at saving it will show degradation. JPEG is the best format for web publishing, so I keep lots of JPEGs floating around for that purpose.

I do archive all of my RAW files onto CD-R. I quit archiving onto CD-RW.

RAW files tend to get converted into TIF files and "refined" for exposure, contrast, or other more controversial factors. That refining generally takes time and skill, which I do not want to throw away, so I archive my refined TIF files also. Generally I leave them all sitting around on each of two hard disks. Then over time I get bored with some of them and erase some on one of the disks. Eventually, I migrate files to new hard disks, so I use DVD+RW for removable media. So, someplace around the room I probably have anywhere from two to five copies of my image files, depending on how good they are. 35mm slides are just a hell of a lot harder to deal with.

---Bob Gross---

[Scottes]

Yes, LZW is lossless and offers pretty good compression. If you use only PS you could save as TIF compressed with ZIP to save even more space. It is slower than LZW to open and save.

As a comparison I saved a 16-bit TIF as straight TIF, LZW, and ZIP. 22 MB, 9.3 MB, and 7.3 respectively.

I always use LZW for the compatibility.