The run time error of ImageToFile in MagickCore

[shiengchyi]

I use the ConstituteImage function to generate a GRAY Level image, then use the ImageToFile function to save the image file in JPEG format.
The version of ImageMagick is 6.5.4-8 2009-10-24 Q16 OpenMP.
Here is the code.

ExceptionInfo *exception;
exception = AcquireExceptionInfo();

Image *img;
img = ConstituteImage(height, width, "I", CharPixel, imgBlobBuffer, exception); //imgBlobBuffer is an Unsigned Char array, and one byte per pixel
ImageToFile(img, Path, exception); //Path is file path like this "./test.jpeg"

I get a run time error at ImageToFile function:
magick/blob.c:1523: ImageToFile: Assertion `image->blob->type != UndefinedStream' failed. Aborted

Does anybody could tell me what wrong is it?

[magick]

Use WriteImage() rather than ImageToFile(). ImageToFile() reads bytes from disk and writes them to the specified file whereas WriteImage() writes the image pixels to disk in the format you specify.

[shiengchyi]

Yeah~ It is wording now!! Thank you very much~!!