Filters and 1-bit/pixel images [CS]

Dear forum,

I'm currently working on a set of Photoshop CS filters (Windows) that all take a grayscale or bitmap image for their input. The grayscale part works fine, but when I try to apply the filter on a bitmap, I get the following error message: "Could not complete the name-of-filter command because the filter module does not work with single channel images". Debugging the plug-in under Visual Studio reveals that the error is raised by Photoshop, since the plug-in's entry point is not called at all. The plug-in's resources seem to be correctly defined, since the filter is not grayed out when the active image is in bitmap mode. Below is an excerpt of the filter's resource file:

SupportedModes
{
doesSupportBitmap,
doesSupportGrayScale,
noIndexedColor,
noRGBColor,
noCMYKColor,
noHSLColor,
noHSBColor,
noMultichannel,
noDuotone,
noLABColor
},

EnableInfo { "in (PSHOP_ImageMode, BitmapMode, GrayScaleMode) &&"
"PSHOP_ImageDepth < 16" },


FormatMaxChannels { {1, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24 } },

FilterCaseInfo
{
{
/* Flat data, no selection */
inStraightData, outStraightData,
writeOutsideSelection,
doesNotWorkWithBlankData,
doNotCopySourceToDestination,

/* Flat data with selection */
inStraightData, outStraightData,
writeOutsideSelection,
doesNotFilterLayerMasks, doesNotWorkWithBlankData,
doNotCopySourceToDestination,

[... etc ...]

Is there another field I should define in the resource files in order to have Photoshop actually call my filter on bitmap images ? Any help and/or example would be appreciated. Thank you in advance.

Nicolas Rudaz