}
		}

		// The current row for y is the previous row for y+1.
		pr, cr = cr, pr
	}

	return img, nil
}

// mergePassInto merges a single pass into a full sized image.
func (d *decoder) mergePassInto(dst image.Image, src image.Image, pass int) {
	p := interlacing[pass]
	var (
		srcPix        []uint8
		dstPix        []uint8
		stride        int