Bands in ImageProcessing

Hi All,
I created bitmap driver to capture the Bitmap image of a given Print Job without printer(I mean my driver is a virtual driver based on microsoft UniDrv).
But I am always getting only one Band which is converted succefully to bitmap file…
I thought that The renderer Plug-in, which is there in DDK(OEMUNI) is capturing the each band Information in Image Processing Module,Hence I tried to captured the given print jobs bitmap
image there in the above module and tried to save to a file, But My image processing Module called only once and I am capturing only a part of the given print job…

Color Mode feature of my GPD file is as follows:
*Feature: ColorMode
*HelpIndex: 12004
*DefaultOption: 24bpp
*Option: 24bpp
*DevBPP: 24
*DrvBPP: 24
*IPCallbackID: 24
*Command: CmdEnableDRC { *Cmd : “” }
*PaletteSize: 256
*PaletteProgrammable? : TRUE
*Command: CmdDefinePaletteEntry {*Cmd : “” }
*Command: CmdSelectPaletteEntry { *Cmd : “” }
*Command: CmdSetSrcBmpWidth { *Cmd : “” }
*Command: CmdSelect
*Order: PAGE_SETUP.16
*Cmd: “”

If I change my *devbpp=0 and *NumofPlanes=0 nothing is saved in my file(I mean My bitmap file conatains Black/White screen.)
I want to know,
When we print a document How many bands will be created ?
How to make ImageProcessing module to be called for each band?
Do I need to modify anything in my GPD?
Am I doing it in right way…
can Anybody help me in this regard.

advanced thanks

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