Kevin Myers wrote:
> As mentioned in my previous message, Photoshop's limit is 32K maximum pixels
> in either dimension. Your image did not exceed this limit in either
> dimension. We typically work with images that are up to several hundred
> thousand pixels in one dimension, by 2 or 3 thousand pixels in the other
> dimension. Thus we almost always exceed the Photoshop limit.
> I presently run GIMP 1.2.4 on a 2.4 GHz P4 based system under Windows 2000,
> with 3GB of RAM installed (only 2GB of which can be used by the GIMP). We
> usually work with 8 bit grayscale images, and as described above our typical
> image sizes are on the order of 200 megapixels. As you mentioned, your
> image was only 98 megapixels. On my system, I have no problems with menu
> delays at all (far less than one second response), and initial image loading
> speed is reasonable, typically on the order of 5 or ten seconds.
Strictly speaking PS 8 (CS) can go larger in pixel dimensions (if
you use the new .PSB file format) but there are other operational
issues that still make this awkward.
But for me it's not the pixel dimensions that define a large image.
As a photographer I work with full RGB images, not piddly little
greyscale files ;-).
I have two systems here. Apples aren't quite apples, but it's a
vaguely interesting comparison anyway:
System A is a 1.6GHz P4 with 512MB RAM, running Gimp 1.2
on FreeBSD. Working with large files (e.g. only 6400x9600
24-bit pixels) can be painful, especially if I decide to
add layers. I've done an A0-sized poster on this machine
and it was ridiculous. I got the job done eventually, but
it was VERY painful.
System B is a PowerMac G4/450 with 1GB RAM. This machine
is old and slow by Apple standards. It's running Photoshop
CS on MacOS X 1.3. It's a pleasure to use in comparison
to System A. The speed difference (and a few other advantages)
has made it worthwhile to get used to the different (Photoshop)
interface. I regularly work with 48-bit image files, at
large print sizes, and with at least 5 or 6 layers. The
filesize when saved as a layered uncompressed TIFF is often
larger than will fit on a CD. As the files get bigger the
processing time increases, but it feels like a simple
geometric progression based on the CPU/megapixel relationship,
not an exponential/whatever progression based on RAM
Sure the Mac has more RAM, but I've tuned Photoshop's RAM allocation
back to 256MB as an experiment and it was still faster than the
Gimp. I normally have 576MB allocated to PS.
In the Gimp there seems to be no upper bound to its RAM use. No
matter what size you set the tile cache to (right nowe I have it
set at 320M) and the number of undo levels, its memory footprint
seems to keep increasing, and when it gets painful it's typically
paging (i.e. it's not managing its own scratch space like Photoshop
does - the OS is paging it in and out). Shutting down other
applications does improve things for a short while, but very soon
that extra memory is chewed up and performance goes down the tube
again. It seems that often the Gimp's active memory footprint is
very large, and information is being paged out that was only just
When the Gimp's performance drops off it's saturating the disks
with VM paging, and the whole machine is painful to use. When
Photoshop's performance drops off it's mainly just hogging CPU and
the rest of the machine is vaguely usable.
I would say that on machines with equivalent RAM sizes Photoshop
is a better performer (on the images I deal with at least) but I
should load Gimp 2 onto the Mac for a better comparison.
Using Photoshop 7 on my wife's XP machine which is a 1.8GHz version
of my System A seems OK, but I haven't done a lot of work with it
as she keeps wanting to use it...
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