Reading depth in mm from ros depth image

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I want to read a depth image from ros. I subscribe to the /camera/aligned_depth_to_color/image_raw/compressed topic published by a intel realsense D435i camera. I get a sensor_msgs CompressedImage ros msg, the image has a 16UC1; jpeg compressed format. I use opencv to read the image: depth_image = bridge.compressed_imgmsg_to_cv2(image_depth,desired_encoding=‘passthrough’) but it returns an image with values between 0-255. How can I get the depth value in mm for each pixel?