This has come up before, and it’s just not there.
Assuming you’re using Windows? Freebie IrfanView will do it fine.
Mac
Yes I am using Windows. Good suggestion….only problem is that the LZW compression on Irfanview hardly compresses at all. I can save a file one by one using elements with TIFF LZW compression and it will be 40-60% of the original size. If I do the same thing in Irfanview it might be 90-110% of the original size. Can’t figure that one out.
I’d say the one you got greater than 100% of original was probably one that had already been LZW compressed, and you did it again. ..zip files will sometimes do that too, on files that were already compressed, like jpeg.
However, I did a test and sure enough, IrfanView’s LZW DOES render a larger final TIFF file size than Elements. I took a 9.4MB TIFF. Elements LZW TIFF: 5.4MB, Iview’s: 7.4
First weak point in IrfanView I’ve ever found.
Mac
Could someone please explain LZW compression to me? What is the difference between LZW compression and JPG compression, other than amount of compression. And how can any compression be "lossless". I thought compression was done by removing pixels.
Thanks.
Eva
In no case does compression routine remove pixels. That would be downsampling. You can take a pic and compresses the crap out of it with JPEG so that it looks positively horrible, but it will have same number of pixels you started with.
One comparison betweeen the two: JPEG takes "similar" values and throws out the differences. TIFF LZW compresses by mapping exact same values only. The former is lossy the latter is lossless.
The more exact same colors you have (or grayscale value), the more effective LZW is. For example for lineart files, where there is only black and white, LZW will compress to 98% or so, still lossless.
There is beau coup more science to both techniques, especially JPEG, but there are the bare essentials. But in no case are pixels thrown out (unless you downsampled at the same time before saving).
Mac
The files I selected had not been saved with compression previously. I sent an email message to IrfanView regarding this subject. Perhaps they will take a look at this. Thanks again for your input Mac. Gary
Mac, Thanks for the explanation. Coincidentally, I went to my local library yesterday to get a book on digital photography. The one I found, "Complete Digital Photography" by Ben Long has a short section on compression. It supports what you say and explains a bit on how the mapping is done.
Thanks again. Eva
Well, "they" is one fellow, Irfan Skiljan, AFAIK. But he does indeed improve Iview about every 6 months or so.
I would have thought there was an existing LZW algorithm that would be coded in equally to anyone’s program, so that it behaved the same from program to program. But what do I know? Certainly not coding.
Mac
