Plotting Very Large Image Files

I recently received a 100 MB raster image file from a client, and to use as a background image in a bathymetric map of a reservoir.  The image was a very high resolution TIFF file, depicting the bottom of the reservoir in great detail, which the client needed to see in his maps.  It looked great in model space, and on the layout tab, but when I tried to plot it to a PDF, the image was absent from the final plot.  The image showed up in a plot preview, but not in the final PDF.

Obviously, plotting is a very tricky thing, and a lot of software and hardware variables come into play.  I found a couple of solutions, and they may help you in a similar situation.

Two new system variables were added to AutoCAD in 2007: RASTERPERCENT and RASTERTHRESHOLD.

The RASTERPERCENT system variable controls the amount of virtual memory available for raster output. The default value is 20, which limits AutoCAD to only use 20% of available virtual memory. While this is adequate for most images, it may not be enough memory for large image files, and can result in incomplete plots, hang -ups, or crashes when plotting.

I bumped this value up to 90%, and combined with changes to the RASTERTHRESHOLD (detailed below), I was able to get my plot out.
The higher the setting, the slower other applications could run while plotting in AutoCAD.  Therefore, if you adjust this system variable, and notice other applications running slowly, reset it to 20 unless you need it higher.

The RASTERTHRESHOLD system variable limits the maximum size of the plot file, in magabytes. The default value is 20, which means that if the plot file is larger than 20 megabytes, the plot may be aborted, or may be incomplete.  A higher setting may be necessary for drawings with large (or multiple) raster images attached.

I bumped this value up to 100, and (when combined with changes to the RASTERTHRESHOLD above), my image appeared in the plot.

Notice the level of detail in the very small (magnified) sample area shown below:


A few weeks later, I got an even larger raster image file from the same client, and this time the above changes to the system variables did not solve my plotting problem; even with the percent of virtually memory increased to 100, and the plot file size increased to 300 megabytes, the image was always absent from my PDF.

Since there are many different types of TIFF files, Rick Ellis came up with an idea.  He suggested I open the image file with a raster editing program (such as Paint Shop Pro, PhotoShop or Snagit), and simply save the file as a new TIFF.  The size of the new file was considerably smaller, but the detail was preserved.  Once I reinserted this new image file, the plot was successful; the plot contained the image.

With so many hardware and software variables there are no guarantees that these techniques will work in every situation, but if you ever have difficulty plotting maps with large background images, they are worth a try.

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