Compressed Tif, is it lossless?

Hi, anyone can tell me if saving a Tif file in compressed format (LZW) is lossless or not? Thank you.

LZW is a lossless algorithm.

You lose a lot of time and compatibility with many applications. You gain very little in terms of disk space with LZW compression of image files. With compression, you also lose redundancy which helps make disk files recoverable. So what's important to you?

Thanks, guys. My only problem is that I'm running short of disk space, despite having one

internal HD plus two external drives for a total of 320 gigs. Until I sort things out and

archive many files on DVD, that is. So, I'm trying to save as much megs as possible. The

same file is 34 meg uncompressed, and 20 meg compressed. That's a lot when you save

like 50 scanned photos.

LZW compression of image files gives very little compression with a typical pictoral "photo image", but adds a bog abit with opening and closing.<BR><BR> BUT in some fields, like maping, billboards, hockey dasher boards, signage, there are images that many times have alot of area with ONE tone, that compresses VERY well, sometimes 1:10 and 1:20. Thus a 50 meg sign might become a manageable 2.5 meg file, emailable even to a slow dialup box in podunk. The comments about LZW being not effective are often in photoshop books and seminars, where folks dont deal with signs, banners, billboards, or printing for the public. LZW is very valueable for compression images in some specialized industries like advertising, and usually abit like boobs on a boar hog for the average joes soccer images, or fine art sunset images. <BR><BR>LZW is lossless, the compression ratio depends on the makeup of the images detail and number of tones. <BR><BR>For engineering drawings where there are 1 bit images, often the group 4 TIFF compression is used, and the compression can be 1:100 of more with a clean drawing. Thus a 30x42" 1 bit drawing is 22.9meg when opened, and many times just 150k to 500k with a group 4 tiff compression method. Modern Photoshop will open a group 4 tiff, but will not create this variant. Open your group 4 TIFF 1 bit image in photoshop, and resave it as a compressed LZW and it will be 10 times larger!

Invest in another external hard drive, or replace your smallest one if you're short of USB ports. I use three Maxtor EHDs for a total of over 400GB, in addition to the 100GB internal drive. I also back everything up to DVD about every six months. The only files I keep on the internal drive are the "Darkroom" files, stuff I'm currently working on. Everything else is in redundant copies on the EHDs.

There are actually several dozen compression methods used in the TIFF format, and several hundred TIFF variants. There were 200+ variants of TIFF a decade ago! <BR><BR>LZW , group 4 and other compression methods are sometimes not supported by some programs. In some cases older photoshop will open a weird compression scheme, and modern photoshop will not. With the old PCX format, I have run into where older photoshop 3.0 will open one clients older stuff, but modern photoshop will not with some engineering drawings. <BR><BR>The group 4 TIFF compression method is really old, actually a fax format. It is common in the printing industry and scanning of engineering drawing industries. 36 inch wide 1 bit drawing Scanners were using group 4 tiff for drawings, before the internet, in the dos area, in the 1980's. <BR><BR>Here one often had a 4800, 9600, modem and was using a 386 with dos and using X modem to transfer files to another factory. For overseas work the radically more robust Hilgraeve Hyperprotocol © was a major breakthru, that actively adjusted the transfer to cope with overseas flakey echos with modem to modem transfers. <BR><BR>Before the internet folks had BBS's, and used manual file transfers at print shops, and for sending images across the world. When fooling with a 9600 modem and 1980's dollar per minute overseas call rates, compression does matter!<BR><BR>

Bernard, its OK to us LZW compresion for photos. Just be carefull if you expect your relative to deal with it if you send him a CD. :) For me while retouching and doing general photoshop work, I onely use LZW for finally saving images like signage, and posters with alot of giant text, where the compression is alot. I rarely use LZW for photos. You might see if your software type(s) are happy with LZW.<BR><BR>Use CS2's bridge, a slower computer, and a zillion LZW files in one directory if you want a massive bog for browsing. :)<BR><BR>In running a print shop, time is money. The LZW bog is unacceptable many times, and only used where warranted, like the final signage file. Once compressed, a LZW or a group 4 file cannot be compressed more with zipping.

Bernard, that's quite good compression. I have some lzw compressed tiffs, 48 bit rgb raw scans from a Minolta Scan Dual II, that shrunk about 20%. I've had no problems opening/using them so far, knock-on-wood. They were created through Vuescan.

 

With my present scanning workflow, I prefer using my current scanner's software to output similar tiff files, but lzw compression is not an option. I have tried lzw compression on these through Photoshop, but end up with files that are actually larger!

 

Just to chime in, yes, lzw is lossless. You could also consider jpeg2000 with lossless option. The compression will likely be significantly better than lzw. I experimented with this, but found I had subsequent problems opening the files in Photoshop. Sometimes I could, sometimes there was a warning about insuficient memory. Not a good sign.

 

Another option is png format. Similar to tiff, lossless, and using compression by default. For me, it's compression is *slightly* better than tiff lzw (created through Vuescan).

 

All of the compressed formats tend to be load slower. Or in the case of jpeg2000, refusing to load.

 

I finally opted for uncompressed tiffs for my current scanning project. I'm getting a whole 20 images per dvd, and will likely need between 80-100 discs before I'm done. Plus, I'm making 2 copies. A few years down the road, I'm sure the "storage issue" will become trivial. Something to keep in mind?

( In running a print shop, time is money. The LZW bog is unacceptable many times, and only used where warranted, like the final signage file. Once compressed, a LZW or a group 4 file cannot be compressed more with zipping. )

 

LZW is most popular universal loseless compression algorithm in the world. Loseless compressed information can't be compressed to infinity ofcourse. If you can compress and overcompress etc. it's sign of very poor compression algorithm.

 

Zip uses the same LZW algorithm.

If you are running out of disk space, you are also running out of time. All disk drives fail - some sooner than others (I have 1 or 2 fail per year, running at least 20 discs).

 

So what are your plans - keep taking photos until your drives fill up or you buy a larger disk? I suggest you need an effective archiving scheme, preferably using optical media. Get them off your hard drive so you have working space for new images - just keep a working set of selected shots on line, and back those up too.

With 16-bit files in Photoshop CS2 (and presumably elsewhere), LZW compression actually increases the size of TIFF files. Even with 8-bit files, LZW compression provides minimal space saving.

 

Lossless JPEG 2000 is the only Photoshop-supported format I've found that provides genuine space savings with 16-bit files. The saving can be up to 30%, which can make a difference with 128-megabyte 4000dpi scans. PNG is another option, but it doesn't support color profiles and metadata and its compression isn't as good. The JPEG 2000 plug-in that comes with Photoshop is slow and clunky.

 

Since I have some doubt about the long-term viability of JPEG 2000, I reserve it for working files. I save finished "master" files as uncompressed TIFF, since that is likely to remain compatible with a variety of applications.

The LZW "compression ratio" depends on the type of image. Do a screen shot of this page and LZW can have a high compression; since there is alot of one tone, ie white. A complex photographic image with alot of details wont compress much at all, and sometimes can grow larger as mentioned. Hard drives do fail, I had a 160Gig 7200 rpm Maxtor crash last week that was only 10 months old, an upgrade to an older 667Mhz Coppermine P3 with 1 gigs of ram, a decent box.