High frequency emphasis amount control device
A first discrete Fourier transform unit generates a first frequency spectrum by two-dimensional discrete Fourier transform of an input image signal. A second discrete Fourier transform unit generates a second frequency spectrum by two-dimensional discrete Fourier transform of an output image signal output from a high frequency emphasis circuit. A first and second high frequency component index generators generate a first and second high frequency component indices indicating a total amount of high frequency components based on the first and second frequency spectra, respectively. A high frequency component emphasis ratio calculator calculates a high frequency component emphasis ratio which is a ratio between a first high frequency component index and a second high frequency component index. An emphasis amount controller generates an emphasis amount control value based on a high frequency component emphasis ratio and a target emphasis ratio, and supplies it to the high frequency emphasis circuit.
1 . A high frequency emphasis amount control device comprising: a processor and memory storing instructions, the processor configured to execute the instructions to perform operations comprising:
generating a first frequency spectrum by performing a two-dimensional discrete Fourier transform of an input image signal;
generating a second frequency spectrum by performing a two-dimensional discrete Fourier transform of an output image signal output from a high frequency emphasis circuit;
determining a first high frequency component index indicating a total amount of high frequency components based on the first frequency spectrum;
determining a second high frequency component index indicating a total amount of high frequency components based on the second frequency spectrum;
calculating a high frequency component emphasis ratio based on a ratio between the first high frequency component index and the second high frequency component index; and
controlling an emphasis amount control value to the high frequency emphasis circuit, wherein the emphasis amount is increased when the high frequency component emphasis ratio is smaller than a target emphasis ratio,
and the emphasis amount is decreased when the high frequency component emphasis ratio is larger than the target emphasis ratio, and the emphasis amount is maintained when the high frequency component emphasis ratio coincides with the target emphasis ratio.
2 . The high frequency emphasis amount control device according to claim 1 , further comprising:
a first weighting calculator configured to process the first frequency spectrum to generate a first frequency spectrum map so as to remove a low frequency component included in the first frequency spectrum and increase a high frequency component; and
a second weighting calculator configured to process the second frequency spectrum to generate a second frequency spectrum map so as to remove a low frequency component included in the second frequency spectrum and increase a high frequency component, wherein
the first high frequency component index generator is a first summation calculator configured to calculate a sum of values of each pixel of the first frequency spectrum map as the first high frequency component index in each frame; and
the second high frequency component index generator is a second summation calculator configured to calculate a sum of values of each pixel of the second frequency spectrum map as the second high frequency component index in each frame.
3 . The high frequency emphasis amount control device according to claim 2 , further comprising:
a first horizontal and vertical frequency components removal unit which removes horizontal and vertical frequency components from the first frequency spectrum map; and
a second horizontal and vertical frequency components removal unit which removes horizontal and vertical frequency components from the second frequency spectrum map.
4 . The high frequency emphasis amount control device according to claim 1 , further comprising:
a first trimming unit configured to perform trimming to cut out a center portion of each frame in the input image signal; and
a second trimming unit configured to perform trimming to cut out a center portion of each frame in the output image signal.
5 . The high frequency emphasis amount control device according to claim 1 , wherein the emphasis amount controller is configured to change the emphasis amount control value by a predetermined time constant or to change the emphasis amount control value according to a predetermined hysteresis characteristic.