}
		if ah != 0 && ah != al+1 {
			return FormatError("bad successive approximation values")
		}
	}

	// mxx and myy are the number of MCUs (Minimum Coded Units) in the image.
	h0, v0 := d.comp[0].h, d.comp[0].v // The h and v values from the Y components.
	mxx := (d.width + 8*h0 - 1) / (8 * h0)
	myy := (d.height + 8*v0 - 1) / (8 * v0)

			// always 1. The component's (h, v) is effectively always (1, 1): even if
			// the nominal (h, v) is (2, 1), a 20x5 image is encoded in three 8x8
			// MCUs, not two 16x8 MCUs.
			h, v = 1, 1

		case 3:
			// For YCbCr images, we only support 4:4:4, 4:4:0, 4:2:2, 4:2:0,
			// 4:1:1 or 4:1:0 chroma subsampling ratios. This implies that the