How to export raw data from DNG?

Hello

I want export Bayer data from my DNG file. I am reading DNG SDK, the dng_validate can parse my DNG file ,there are four lossless jpg in the file. But I can't find the rule to make a RAW data file.

ConstPixel can get a buffer, but can't preview the buffer in Photoshop.

Is there any explain about  the order of RGGB in the ConstPixel, or and document specifies how to convert the four planes jpg to a bayer raw data?

Thanks