Image processing device, image processing method, and computer-readable recording medium

An image processing method for extracting pixels of a specific color from an image to be processed, the image processing method comprising:

• (a) a step of extracting values of luminance, first chrominance, and second chrominance of pixels composing the image on a pixel-by-pixel basis;
• (b) a step of calculating, on a pixel-by-pixel basis, a distance from a point defined by the extracted values to a preset reference plane in a space in which the luminance, the first chrominance, and the second chrominance are set along axes that are perpendicular to one another;
• and
• (c) a step of generating an image in which pixels satisfying the following condition are emphasized:
• the distance calculated in step (b) is larger than or equal to a threshold,
• wherein step (b) calculates the distance by substituting the extracted values into a preset formula on a pixel-by-pixel basis, and the formula is set such that the calculated distance is larger for the pixels of the specific color than for pixels of colors other than the specific color,
• wherein the image generated by the converted image generation unit emphasizes the pixels of the specific color,
• wherein provided that the luminance, the first chrominance, and the second chrominance are expressed as Y, U, and V, respectively, the formula is D=aY+bU+cV+d,
• wherein coefficients a, b, c, and d in the formula are set such that the distance D calculated using the formula is larger than or equal to zero for the pixels of the specific color, and smaller than zero for the pixels of colors other than the specific color, and
• wherein the specific color is yellow.

A non-transitory computer-readable recording medium having recorded therein a program for extracting pixels of a specific color from an image to be processed using a computer, the program including an instruction to cause the computer to execute:

• (a) a step of extracting values of luminance, first chrominance, and second chrominance of pixels composing the image on a pixel-by-pixel basis;
• (b) a step of calculating, on a pixel-by-pixel basis, a distance from a point defined by the extracted values to a preset reference plane in a space in which the luminance, the first chrominance, and the second chrominance are set along axes that are perpendicular to one another;
• and
• (c) a step of generating an image in which pixels satisfying the following condition are emphasized:
• the distance calculated in step (b) is larger than or equal to a threshold,
• wherein step (b) calculates the distance by substituting the extracted values into a preset formula on a pixel-by-pixel basis, and the formula is set such that the calculated distance is larger for the pixels of the specific color than for pixels of colors other than the specific color,
• wherein the image generated by the converted image generation unit emphasizes the pixels of the specific color,
• wherein provided that the luminance, the first chrominance, and the second chrominance are expressed as Y, U, and V, respectively, the formula is D=aY+bU+cV+d,
• wherein coefficients a, b, c, and d in the formula are set such that the distance D calculated using the formula is larger than or equal to zero for the pixels of the specific color, and smaller than zero for the pixels of colors other than the specific color, and
• wherein the specific color is yellow.