  The dynamic range of our normal life can exceeds 120 dB, however, the
smart-phone cameras and the conventional digital cameras can only capture a
dynamic range of 90 dB, which sometimes leads to loss of details for the
recorded image. Now, some professional hardware applications and image fusion
algorithms have been devised to take wide dynamic range (WDR), but
unfortunately existing devices cannot display WDR image. Tone mapping (TM) thus
becomes an essential step for exhibiting WDR image on our ordinary screens,
which convert the WDR image into low dynamic range (LDR) image. More and more
researchers are focusing on this topic, and give their efforts to design an
excellent tone mapping operator (TMO), showing detailed images as the same as
the perception that human eyes could receive. Therefore, it is important for us
to know the history, development, and trend of TM before proposing a
practicable TMO. In this paper, we present a comprehensive study of the most
well-known TMOs, which divides TMOs into traditional and machine learning-based
category.
