Patent ID: 7804895

Claim:
An apparatus for detecting a letter box, comprising: a processing area filter selecting a processing area of an image used to detect the letter box; an intra-macroblock filter calculating a change level of pixels in one line of the image from the processing area, and determining whether the corresponding line belongs to the letter box area by comparing the calculated change level of the pixel in one line with a first threshold value; an impulse data filter detecting a high frequency component from the line determined to be included in the letter box in the intra-macroblock filter; an inter-macroblock filter calculating a change level of an image with respect to the line that does not have the high frequency component, and determining whether the corresponding line belongs to a letter box area by comparing the change level of the image in one line with a third threshold value; an inter-line filter determining a boundary of the letter box by comparing the line determined to be included in the letter box in the inter-macroblock filter with an average of the pixel values of adjacent lines; and an inter-picture filter repeatedly performing operations of the processing area filter, the intra-macroblock filter, the impulse data filter, the inter-macroblock filter, and the inter-line filter as many times as the number of the image previously set, and outputting a boundary value of the letter box that has the highest frequency number among the performed results.