6/1/2012
The third step is to name the chart, select the number of colors and save the chart. For some images the number of colors makes a difference in quality; for others quality is maintained even with fewer colors. By adjusting the number of colors it is sometimes possible to reduce the file size by a factor of 2 without loss in quality.
The picture on the left is a screen shot of step three for Raster Charts.
To define the desired number of colors select from the choices in the pull-down. As you change the number of colors the displayed image and file size will reflect your choice.
As with the Resolution Window, an overview of the chart image and scroll bars are provided to aid in previewing the magnified chart image of your selected area. What you see here is what you will see when you zoom in on the saved chart.
After selecting the number of chart colors press the 'Save Raster' button.
Note: The NOAA chart specification requires that the number of colors be less than 128.
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