Regarding, projecting 3D point onto the image plane of the camera. (YT video skipped in part1)

[BahMoh]

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[BahMoh]

In the provided code we see along the code cell [26] and [27], after moving the some_point 3D point into the left camera coordinate frame, the code only uses k1 intrinsic matrix to project the point (in the left cam coordinate frame) onto the 2D image plane.
Shouldn't we use the complete projection matrix?
I mean P1 = k1[r1|t1]