Ping is similar to read except only enough of the image is read to determine the image columns, rows, and filesize. The columns, rows, and fileSize attributes are valid after invoking ping. The image data is not valid after calling ping.
See Implementation
Ping is similar to read except only enough of the image is read to determine the image columns, rows, and filesize. The columns, rows, and fileSize attributes are valid after invoking ping. The image data is not valid after calling ping.