case nil:
		src = &image.Uniform{C: color.RGBA{0x11, 0x22, 0x33, 0x44}}
	case color.CMYKModel:
		src1 := image.NewCMYK(image.Rect(0, 0, srcw, srch))
		for y := 0; y < srch; y++ {
			for x := 0; x < srcw; x++ {
				src1.SetCMYK(x, y, color.CMYK{
					uint8(13 * x % 0x100),
					uint8(11 * y % 0x100),
					uint8((11*x + 13*y) % 0x100),
					uint8((31*x + 37*y) % 0x100),
				})
			}
		}
		src = src1
	case color.GrayModel: