From Tracker Software PDF SDK
The method inverts color data only within the specified color channel.
HRESULT InvertChannel([in] IXC_Channel nChannel, [in] RECT* stRect);
- [in] Specifies the Channel for which function should be applied.
- [in] Pointer to a RECT structure which defines the rectangular area where he colors should be inverted. If this parameter is NULL, then the entire page will be inverted.
Note:Please note that processing part of the page is not supported for some internal formats. For example, it is not supported for indexed images, because the pixels in such images do not contain the color, but an index into a color table (or palette) which is common for the entire page.
Returns S_OK if operation was successful or error code in other cases.