Abstract: An image-signal processing unit comprising a first and second luminance calculation block, a correction-value calculation block, and a subtraction block, is provided. The first luminance calculation block calculates a first luminance corresponding to the sum of a plurality of primary color light components. Each of them is multiplied by a coefficient from a first coefficient combination. The second luminance calculation block calculates a second luminance corresponding to the sum of a plurality of the primary color light components. Each of them is multiplied by a coefficient from a second coefficient combination. The correction-value calculation block calculates a luminance correction value according to the second luminance if the first luminance is greater than a threshold value. The subtraction block calculates a corrected luminance by subtracting the luminance correction value from the first luminance.

Abstract: An endoscope processor including a light source controller, an imaging device driver, and a gamma-correction block, is provided. The light source controller can order first and second light sources to alternately emit first and second lights, respectively. The imaging device driver orders an imaging device to generate first and second image signals by capturing an optical image of a subject while the firs and the second light are shone on the subject, respectively. The gamma-correction block carries out gamma correction on the first and second image signals using first and second color gamma coefficients, respectively. The first and second color gamma coefficients are predetermined according to the wavelength band of the first and second lights.

Abstract: An electronic endoscope system comprises a video-scope, an imaging device, and a black balance processor. The imaging device, which is provided on the video-scope, is exposed at a normal shutter speed so as to generate an image signal corresponding to an optical image that is formed thereon. The black balance processor generates a black balance value for adjusting the black balance of the image signal, based on a black image signal corresponding to a black image. The black image signal is generated by exposing the imaging device at a high shutter speed that is faster than the normal shutter speed.

Abstract: An endoscope processor including a light source controller, an imaging device driver, and a gamma-correction block, is provided. The light source controller can order first and second light sources to alternately emit first and second lights, respectively. The imaging device driver orders an imaging device to generate first and second image signals by capturing an optical image of a subject while the firs and the second light are shone on the subject, respectively. The gamma-correction block carries out gamma correction on the first and second image signals using first and second color gamma coefficients, respectively. The first and second color gamma coefficients are predetermined according to the wavelength band of the first and second lights.

Abstract: An image-signal processing unit comprising a first and second luminance calculation block, a correction-value calculation block, and a subtraction block, is provided. The first luminance calculation block calculates a first luminance corresponding to the sum of a plurality of primary color light components. Each of them is multiplied by a coefficient from a first coefficient combination. The second luminance calculation block calculates a second luminance corresponding to the sum of a plurality of the primary color light components. Each of them is multiplied by a coefficient from a second coefficient combination. The correction-value calculation block calculates a luminance correction value according to the second luminance if the first luminance is greater than a threshold value. The subtraction block calculates a corrected luminance by subtracting the luminance correction value from the first luminance.

Abstract: An electronic endoscope system comprises a video-scope, an imaging device, and a black balance processor. The imaging device, which is provided on the video-scope, is exposed at a normal shutter speed so as to generate an image signal corresponding to an optical image that is formed thereon. The black balance processor generates a black balance value for adjusting the black balance of the image signal, based on a black image signal corresponding to a black image. The black image signal is generated by exposing the imaging device at a high shutter speed that is faster than the normal shutter speed.

Abstract: An electronic endoscope system has a light source unit that is capable of selectively emitting normal-light and exciting-light, and a video-scope with an image sensor, which has an exciting-light eliminating or cutoff filter, and an image processor that processes image signals read from the image sensor. The image signal processor processes the image signals so as to compensate for a change of at least one of luminance and color in an observed image that occurs due to light blocked in accordance with the spectrum transmittance characteristics of the exciting-light eliminating filter.