1. A picture quality controlling device that controls a picture quality for an image signal which is input, the picture quality controlling device comprising: a histogram generation unit configured to generate a histogram for at least one of a brightness information piece, a chromaticity information piece, a color information piece, and a frequency information piece, the brightness, chromaticity, color, and frequency information pieces being obtained from an image contained in the image signal; a threshold value comparing unit configured to compare the histogram generated by the histogram generation unit with a threshold value previously set for each of the histogram in order to determine whether control of the picture quality for the image signal is necessary; and a picture quality controlling unit configured, if the control of the picture quality for the image signal is determined to be necessary based on a result obtained by the threshold value comparing unit, to extract a histogram pattern corresponding to the histogram generated by the histogram generation unit from a reference table including a plurality of predetermined histogram patterns, and control the picture quality for the image signal based on a controlled parameter corresponding to the extracted histogram pattern.