I change the mode of my figure to Grayscale in the gimp and export it in the .eps format. But my output .eps figure still has CMYK mode. Is any other action that I most do to have a 8-bit gray image?
Open image in photoshop. Convert it to grayscale by Image>Mode. Save As it to .eps. There are 3 options to select .eps - (1) Photoshop EPS (.EPS) (2) Photoshop DCS 1.0 (.EPS) (3) Photoshop DCS 2.0 (.EPS). Choose only Photoshop EPS (.EPS). Then EPS option dialogue box appears. Here select Preview>TIFF(8 bit/pixel) and Encoding>Binary. Then Save it.