Help! What's matter with my raster data?

[Horky Chen]

Dear all,
   I write one filter to package the raster data to our format. I use the CMYK color space, and color order is Chunked. When print one cyan color image,but the result I get via cupsRasterReadPixels cannot match the source data. For example, the color of my image is:
  C:0   M:79  Y:0  K:0, but I get from the Raster data, it be:
  C:34  M:67  Y:0  K:0!  That's why? Why I cannot get the real image data from CUPS Raster data?

Thanks in advance?