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Increasing Performance

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Jonathan Wiggins
Posted on Monday, October 16, 2000 - 8:10 pm:   Edit PostDelete Post

I am using a PIII 500 with 256 Mb of RAM. I am stitching together three 1280x1024 into a column making a image of about 950x2200 and then stitching 24 of these together into a Quicktime panorama. I have got to the stage where I am running a page file which is over 3Gb and performance is very slow. Obviously when dealing with such large images I don't expect lightning performance but have you got any ideas? It is taking about an hour to stitch the 24 images together.
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John Strait
Posted on Saturday, November 04, 2000 - 11:37 am:   Edit PostDelete Post

The fact that your paging file has grown to 3 G suggests that you are having a memory problem.

The first thing is to be sure you have the latest release of The Panorama Factory. V2.2 corrected a problem that caused memory usage to be less efficient than it should be.

Next, make sure you have enough RAM. Without enough RAM, the fastest CPU won't make much difference.

Also, be sure you have not selected Keep all images in memory on the Project properties dialog (File menu). This may make things run a little faster...but only if you have enough RAM to hold all images (including temporary images) in memory at the same time. If you do not have enough RAM, this option will make PF run slower because you will invoke Windows virtual memory swapping.

You must have enough RAM to hold the "working set" of the program. The term "working set" means the data that the program needs to have in memory at the same time.

If there is not enough RAM to hold all of the data needed by a program, Windows must write some of the data to disk and read it later when it is needed -- a process called "swapping." (This is a very, very simplified explanation of virtual memory.) If the working set cannot fit in memory at once, swapping goes on almost continuously -- a condition called "thrashing." When the computer is thrashing, very little useful work gets done.

Unfortunately, there is no simple way to be exactly certain of the working set size.

During stitching, you need to be able to hold the finished image plus two imported images (plus the program, plus Windows, etc.) in RAM at one time. I'm guessing that your finished image is probably somewhere between 150 M and 200 M and your column images are about 8 M. Your working set size is probably close to 200 M!

There is, however, a simple way to determine whether or not The Panorama Factory is thrashing. During stitching, watch the hard disk activity light on your computer and also watch the progress bar that tells what PF is doing. If the disk is active only when PF indicates it is reading or writing image files, you are probably OK. If there is a lot of disk activity at other times, PF is probably thrashing.

Once you are certain you have enough memory, a faster CPU will help.

You may also consider upgrading the speed of your disk. Even when there is enough RAM, PF still performs many disk reads and writes. Your images are very large, so PF must read and write very large files. I have found that having a faster disk can make a significant difference in performance.

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