MagickSetImageType and gm convert: inconsistent behaviour

Hi all,

I have encountered some inconsistent behaviour between the  
MagickSetImageType call the the "convert" option inside the gm command  
line tool.

What we need to do is set the type of a greyscale image back to the  
truecolor space (we are aware our color isn't going to come back :)) ,  
and normally as I understand you would use MagickSetImageType to do  
this (is that correct?).

In the past we have used the gm command line tool to do this, and this  
has always worked, however when we've changed it to use our own code  
calling MagickSetImageType, the ImageType refuses to change away from  
grayscale.

Digging in the source, we find the reason SetImageType isn't changing  
the image type is because it believes the image is already in the RGB  
colourspace:

2736	  switch (image_type)
(gdb)
2735	  logging=IsEventLogging();
(gdb) print image_type
$1 = TrueColorType
(gdb) next
2736	  switch (image_type)
(gdb)
2888	      if (!IsRGBColorspace(image->colorspace))
(gdb) print image->colorspace
$2 = RGBColorspace

Is a grayscale image supposed to be in the RGB colourspace, and am I  
misunderstanding this?

It turns out the reason the gm tool's "convert" function "works" is  
because the convert function cheats and hardcodes the ImageType direct  
into a private structure within the image:

         if (LocaleCompare("type",option+1) == 0)
           {
             resource_info.image_info->type=UndefinedType;
             if (*option == '-')
               {
                 i++;
                 if (i == argc)
                    
MagickFatalError(OptionFatalError,MissingArgument,option);
                 option=argv[i];
                 resource_info.image_info- 
 >type=StringToImageType(option);
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                 if (resource_info.image_info->type == UndefinedType)
                    
MagickFatalError(OptionFatalError,UnrecognizedImageType,
                                    option);
               }
             break;
           }
         MagickFatalError(OptionFatalError,UnrecognizedOption,option);

I am now confused - which behaviour is correct, the SetImageType()  
function that does all the colourspace conversion, or the "convert"  
function that hardcodes the ImageType value into the private structure  
directly?

Why would the SetImageType() function think that a grayscale image is  
already in the RGB colourspace (unless it I am misunderstanding it)?

Regards,
Graham
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