  Deep learning has made great strides for object detection in images. The
detection accuracy and computational cost of object detection depend on the
spatial resolution of an image, which may be constrained by both the camera and
storage considerations. Compression is often achieved by reducing either
spatial or amplitude resolution or, at times, both, both of which have
well-known effects on performance. Detection accuracy also depends on the
distance of the object of interest from the camera. Our work examines the
impact of spatial and amplitude resolution, as well as object distance, on
object detection accuracy and computational cost. We develop a
resolution-adaptive variant of YOLOv5 (RA-YOLO), which varies the number of
scales in the feature pyramid and detection head based on the spatial
resolution of the input image. To train and evaluate this new method, we
created a dataset of images with diverse spatial and amplitude resolutions by
combining images from the TJU and Eurocity datasets and generating different
resolutions by applying spatial resizing and compression. We first show that
RA-YOLO achieves a good trade-off between detection accuracy and inference time
over a large range of spatial resolutions. We then evaluate the impact of
spatial and amplitude resolutions on object detection accuracy using the
proposed RA-YOLO model. We demonstrate that the optimal spatial resolution that
leads to the highest detection accuracy depends on the 'tolerated' image size.
We further assess the impact of the distance of an object to the camera on the
detection accuracy and show that higher spatial resolution enables a greater
detection range. These results provide important guidelines for choosing the
image spatial resolution and compression settings predicated on available
bandwidth, storage, desired inference time, and/or desired detection range, in
practical applications.
