Image processing apparatus and method of enhancing visibility of displayed image

An image processing method comprising:

• sensing a brightness of an external light;
• calculating the contrast of the input image by calculating the contrast of the input image as a slope of a line connecting points at which a cumulative distribution function meets a low range threshold value and a high range threshold value, respectively;
• reading a luminance-contrast model curve representing an optimal contrast value for a particular luminance of each brightness of the external light;
• determining a target luminance value according to the sensed brightness of the external light, obtaining a contrast value corresponding to the target luminance value with reference to the luminance-contrast model curve corresponding to the sensed brightness of the external light, and adjusting an input image to have the target luminance value and the obtained contrast value;
• and
• adjusting a saturation of the adjusted input image by increasing the saturation of the input image when the luminance and the contrast of the input image are increased after the adjustment of the input image, and by decreasing the saturation of the input image when the luminance and the contrast of the input image are decreased after the adjustment of the input image.

An image processing method comprising:

• detecting an external luminance of an external environment;
• detecting an input luminance and an input contrast of an input image;
• obtaining one or more stored luminance-contrast model curves corresponding to the external luminance;
• determining a target luminance based on the detected input luminance and a target contrast corresponding to the target luminance from at least one of the stored luminance-contrast model curves;
• adjusting the input luminance and the input contrast of the input image to those of the target luminance and the target contrast, respectively, for subsequent display of the input image;
• and
• adjusting a saturation of the adjusted input image by increasing the saturation of the input image when the luminance and the contrast of the input image are increased after the adjustment of the input image, and by decreasing the saturation of the input image when the luminance and the contrast of the input image are decreased after the adjustment of the input image,
• wherein the detecting of the input contrast of the input image comprises calculating the contrast of the input image as a slope of a line connecting points at which a cumulative distribution function meets a low range threshold value and a high range threshold value, respectively.

An image processing apparatus comprising:

• a storage to store one or more stored luminance-contrast model curves corresponding to an external luminance of an external environment;
• and
• a processor to detect the external luminance, to receive an input image having an input luminance and an input contrast, to obtain one or more stored luminance-contrast model curves corresponding to the external luminance, to determine a target luminance based on the detected luminance and a target contrast corresponding to the target luminance from at least one of the stored luminance-contrast model curves stored in the storage, to adjust the input luminance and the input contrast of the input image to those of the target luminance and the target contrast, respectively, and to adjust a saturation of the adjusted input image by increasing the saturation of the input image when the luminance and the contrast of the input image are increased by the processor, and by decreasing the saturation of the input image when the luminance and the contrast of the input image are decreased by the processor, for subsequent display of the input image,
• wherein the processor calculates a contrast value of the input image by calculating the contrast of the input image as a slope of a line connecting points at which a cumulative distribution function meets a low range threshold value and a high range threshold value, respectively.