Digital BW, The Print

On Dec 4, 2004, at 10:00 PM, Anthony G. Atkielski wrote:

>
> The Wogster writes:
>
>> For archiving though, where you are not looking at the image on a
>> regular basis, you can use other compression mechanisms.  For example 
>> if
>> you can compress a 600MB file down to say 50MB for archiving, and then
>> decompress it again later, who cares?  Even if it takes an hour to
>> compress/decompress.
>
> Agreed.  But what file formats would be in this category?
>
> Theoretically, you could compress most image files enormously with no
> loss, given time and space to do an absolutely optimal compression.
> I've never heard of a file format that is designed for this purpose,
> though.

No - assuming no loss, there are real limits to how far compression can 
take you. It's closely related to Shannon's Law.

However, what you say is very true if you allow for a little loss... 
then yes, we can keep devising deeper, more sophisticated, lossy 
compressors that take more and more memory and CPU. But if the 
requirement is lossless, then we can do pretty nearly optimal 
compression today - even throwing tons more CPU at it with much more 
complex lossless algorithms you'll never get past Shannon.

Today, the best compressors for really great efficiency on really high 
rez materials tends to be wavelets... JPEG2000 and MrSid are both 
popular implementations. The artifacts are much less obnoxious than 
DCT, and the compression ratios are much better. For really large 
images, unless you regularly view them at 100% then a wavelet 
compressor (or even DCT) can be used pretty heavily without losing too 
much significant detail.

Best,

Roger