Problem with -units

It has been brought to my attention that there is a design flaw with 
-units.  The current support code is similar to:

         if (LocaleCompare("units",option+1) == 0)
           {
             image_info->units=UndefinedResolution;
             if (*option == '-')
               {
                 i++;
                 if (i == argc)
                   ThrowConvertException(OptionError,MissingArgument,option);
                 option=argv[i];
                 image_info->units=UndefinedResolution;
                 if (LocaleCompare("PixelsPerInch",option) == 0)
                   image_info->units=PixelsPerInchResolution;
                 if (LocaleCompare("PixelsPerCentimeter",option) == 0)
                   image_info->units=PixelsPerCentimeterResolution;
               }
             break;
           }

The problem is with a command like:

   gm convert in -units PixelsPerCentimeter -resample 762x762 out

Note that in this case, the interpretation of the existing image 
resolution is lost entirely.  In fact, it is currently only valid to 
use -units in conjunction with -density.

I am planning to change the handling so that if the image has an 
existing units value, that the associated image resolution values are 
adjusted to match the new units scale.  That way the existing image 
resolution is not trashed by changing the resolution units.

The command

  gm convert in -units PixelsPerCentimeter -density 762x762 out

would still work as before.

Does anyone see a problem with this approach?

Bob
======================================
Bob Friesenhahn
[email protected]
http://www.simplesystems.org/users/bfriesen


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