stereo camera calibration app for low resolution depth camera

Hi, I am trying to calibrate the depth and RGB cameras to find out the extrinsic parameters, i.e. the rotation and translation matrix. However, my depth camera has only 60*80 resolution, and my rgb resolution is 480*640. What I have done is to first resize the rgb picture down to 60*80 and then use the matlab stereo calibration app to calibrate the two cameras. However, as the resolution is too small, it is hard for matlab to detect all the cross points of the checkerboard of my depth picture, and even if the app did detect all the cross points on checkerboard, it is not very accurate.

I have thought of some solutions, one is to enlarge my checkerboard and let each small square cover as many pixels as possible, and the problem is also obvious: when I increase the distance between the camera and the checkerboard, the checkerboard needs to be very large in order to be clearly detected as the resolution is only 60*80. Maybe, can anyone who has the experience of using matlab calibratoin app to deal with low resolution picture give me some advice of how I can solve this problem.

Thanks in advance!