Hi Dana,
I have just scanned an image and saved it as compressed and
non-compressed files. This particular image surprised me in that it
compressed to a remarkable degree, from 55.3mb to 16.5mb. I presume
different images will compress to different degrees depending on their
content. But, I still disagree that it should take so long to open an image.
The uncompressed file opened in 4 seconds flat and the compressed file
opened in 6.95 seconds - I'm quite sure there is nothing wrong with this
computer.
Geoff
----- Original Message -----
From: "Dana Trout" <dana@troutcom.com>
<filmscanners@halftone.co.uk>
Sent: Monday, July 30, 2001 8:29 AM
Subject: Re: filmscanners: Scanning and memory limits in Windows
> Now that I see you are stating load times for uncompressed files I see
> our times are much more similar. LZW compression is very CPU-intensive
> and there is no comparison between load times for non-compressed and
> compressed files (other than compressed files take a *lot* longer).
>
> I compress TIFFs before putting them on CDs because it's much easier to
> manage 800 CDs than it is to manage over 1200 CDs. The reason I see a
> fairly large compression ratio is that I am saving 48-bit TIFFs, but
> the scanner uses only about 40 of them.
>
> There *is* a big hit in load and store times, though, which is the
> reason I compress *only* what's going onto the CDs. Images that are
> being played with are left uncompressed to reduce the file-handling
> times (even though the files are much larger).
>
> The upshot of this conversation is to point out (yet again) that one
> needs to look at where the bottlenecks really are. If the process is
> largely CPU-bound, as loading and storing LZW-compressed TIFFs are on
> my computer, I will realize much greater gains if I spend money to
> upgrade the CPU than if I get 10,000 rpm drives. Others who have fast
> processors and do not use LZW compression may well find their hard
> drives are the bottleneck and would be far better off upgrading them.
> It is up to each person to investigate where the bottlenecks are in
> *their own* processes and act to relieve them, instead of just assuming
> they need a particular item (faster hard drives, more RAM, or
> whatever).
>
> As for "mucking about" with the image, lossless compression schemes
> like LZW merely encode the values in different bits than straight
> binary. It's really a code similar to Morse code -- the most popular
> values are stored in fewer bits, and the least popular take lots and
> lots of bits but because there are so few instances of them the overall
> number of bits (and therefore bytes) needed to store the image is
> reduced. As for questions about how lossless the process is, just do a
> file compare between the original uncompressed image and one that has
> been retrieved from a compressed TIFF. I have yet to see anything other
> than an exact match -- if there is a difference there is something
> definitely wrong with the computer!
>
> Ta for now,
> --Dana
> ----------
> From: geoff murray <geoffmurray@primus.com.au>
> To: filmscanners@halftone.co.uk
> Subject: Re: filmscanners: Scanning and memory limits in Windows
> Date: Saturday, July 28, 2001 7:21 PM
>
> Hi Dana,
> I never bother to compress TIFF's, apparently there is not
> much
> space saving anyway and I believe the less an image is mucked about
> with the
> better, even if people say that LZW compression is lossless.
>
> Geoff
>
>
> ----- Original Message -----
> From: "Dana Trout" <dana@troutcom.com>
> To: <filmscanners@halftone.co.uk>
> Sent: Sunday, July 29, 2001 5:49 AM
> Subject: Re: filmscanners: Scanning and memory limits in Windows
>
>
> > I find that little of the time spent is due to the disk drive, which
> is
> > the reason for my comment that a 7200 rpm drive, even though it is
> 33%
> > faster than a 5400 rpm drive, will not necessarily reduce load times
> by
> > a like percentage.
> >
> > As for my times being slow, you're right: I was quoting the
> performace
> > of my "junker" computer which is used only for scanning -- it's a 466
> > Celeron with 512MB RAM but Intel's woefully undersized L2 cache.
> > However, the times you quote make me wonder if you are loading
> > LZW-compressed TIFFs. If so, it is *definitely* time for me to
> upgrade
> > the scanner computer!
> >
> > Thanks for your comments,
> > --Dana
> > ----------
> > From: geoff murray <geoffmurray@primus.com.au>
> > To: filmscanners@halftone.co.uk
> > Subject: Re: filmscanners: Scanning and memory limits in Windows
> > Date: Saturday, July 28, 2001 6:15 AM
> >
> > Hi Dana,
> > Gee your times seem very slow. I tried loading a 56mb
> file
> > from
> > my scratch disk and it took 3.6 seconds. A 169mb file took 17
> seconds.
> > This
> > on a Win 98SE machine with a 1Ghz Athlon and 512mb of PC133 ram and
> two
> > 7200rpm hard drives. Scratch partition is not on the hard drive which
> > has
> > PS6. 7200 rpm drives made a significant difference to overall speed.
> >
> > Geoff Murray
> > www.geoffmurray.com
> >
> > ----- Original Message -----
> > From: "Dana Trout" <dana@troutcom.com>
> > To: <filmscanners@halftone.co.uk>
> > Sent: Saturday, July 28, 2001 7:40 AM
> > Subject: RE: filmscanners: Scanning and memory limits in Windows
> >
> >
> > > A 25% faster drive won't necessarily get you 25% faster load/store
> > > times. PhotoShop seems to be inordinately slow in dealing with
> > > compressed TIFFs -- I got curious so I set up a cache large enough
> to
> > > hold the whole file (53MB). The first time I loaded it into
> PhotoShop
> > > it took 61 seconds (reading from the disk). I then closed the file
> > and
> > > reloaded it into PhotoShop (this time from the cache -- the disk
> > light
> > > never even blinked) and it took 55 seconds. And I'm reasonably sure
> > > that a RAM cache is *much* faster than a 7200 rpm drive!
> > >
> > > BTW, Ed's VueScan takes less than 30 seconds to read the same file.
> > > --Dana
> > > ----------
> > > From: Rob Geraghty <harper@wordweb.com>
> > > To: filmscanners@halftone.co.uk
> > > Subject: filmscanners: RE: filmscanners: Scanning and memory limits
> > in
> > > Windows
> > > Date: Friday, July 27, 2001 12:22 AM
> > >
> > > < snip >
> > >
> > > On the other hand I'm reasonably sure the main
> > > bottleneck in my PC when dealing with large scans is the 5400RPM
> IDE
> > > drive.
> > > A 7200RPM drive would speed up loading and saving files by at
> least
> > > 25%.
> > > Two 7200rpm drives in a RAID array should be significantly better
> > > still.
> > > Loading and saving files is the no.1 timewaster for me when
> working
> > > with
> > > film scans on my PC.
> > >
> > > Rob
> > >
> > >
> > > Rob Geraghty harper@wordweb.com
> > >
> > >
> > >
> > >
> >
>
