Black/white stretching system using R G B information in an image and method thereof

An apparatus to stretch a black/white contrast range, comprising:

• a transformer to convert a luminance and a color difference of at least one pixel of an image signal to a plurality of gray levels that correspond to a plurality of color components in the at least one pixel, and the plurality of gray levels are between a black value and a white value;
• a mapper to adjust gray levels outside an intermediate gray level range to one of the black value and the white value;
• and
• an output unit to output an image signal including the at least one pixel having the adjusted gray levels.

A method of improving contrast in a two tone image reproducing apparatus, the method comprising:

• receiving an input image signal having a plurality of pixels with a plurality of color component values and deriving a plurality of gray level values in a predetermined range to correspond with the plurality of pixels from the plurality of color component values;
• mapping first gray level values among the derived plurality of gray level values that are less than a first threshold to a minimum gray level value and mapping second gray level values among the derived plurality of gray level values that are greater than a second threshold to a maximum gray level value;
• and
• outputting an image signal having the plurality of pixels including pixels having the mapped gray level values.

A method of stretching a black/white contrast range, the method comprising:

• converting a luminance and a color difference of at least one pixel of an image signal to a plurality of gray levels that correspond to a plurality of color components in the at least one pixel, and the plurality of gray levels are between a black value and a white value;
• adjusting gray levels outside an intermediate gray level range to one of the black value and the white value;
• and
• outputting an image signal including the at least one pixel having the adjusted gray levels.

A black/white stretching method using R, G, B information of an image, the method comprising:

• transforming a luminance value (Y) and a color difference value of an input image to R, G, B values of each pixel;
• estimating a histogram distribution by accumulating each of the transformed R, G, B values of each pixel in the input image with a same weight;
• generating mapped R′, G′, B′ values by mapping the transformed R, G, B values according to a predetermined mapping function generated based on the estimated histogram distribution;
• and
• generating an output image by reverse-transforming the mapped R′, G′, B′ values to an updated luminance signal and an updated color difference signal.