Image processing apparatus, method and program
An image analysis unit analyzes an image S 0 and sets a dynamic range compression rate P 0 . The image analysis unit calculates saturation of each of a plurality of pixels of the image S 0 and counts a pixel number of high saturation pixels of which saturation is equal to or higher than a predetermined threshold value. If the pixel number of the high saturation pixels is larger than a predetermined threshold value, a new dynamic range compression rate P 1 which is lower than the set dynamic range compression rate P 0 is set. A compression table creation unit creates a compression table T 0 based on the dynamic range compression rates P 0 and P 1. A compression processing unit obtains a processed image data set S 1 by compressing a dynamic range of the image S 0 by using the compression table T 0 . An image output unit prints out the processed image data set S 1.
1 . An image processing apparatus comprising:
a dynamic range compression means for obtaining a processed image of which dynamic range has been compressed by compressing a dynamic range of a color image;
a compression rate setting means for setting a dynamic range compression rate for compressing the dynamic range of the color image based on the dynamic range of the color image;
a compression rate changing means for calculating saturation of each of pixels in the color image, counting a pixel number of high saturation pixels of which saturation is higher than a first threshold value, and if the pixel number is equal to or larger than a second threshold value, setting a new dynamic range compression rate which is lower than the dynamic range compression rate set by the compression rate setting means; and
a compression table creation means for creating a compression table based on one of the dynamic range compression rate and the new dynamic range compression rate.
2 . An image processing apparatus as defined in claim 1 , wherein the compression rate setting means creates a histogram of an image data set representing the color image, calculates a dynamic range of the color image based on the histogram, and sets a dynamic range compression rate for each of an area of relatively high data values, an area of relatively low data values and/or a whole area of the image data set based on the dynamic range by using a predetermined standard value of the image data set as a standard.
3 . An image processing apparatus as defined in claim 1 , wherein the compression rate changing means sets the new dynamic range compression rate by lowering the dynamic range compression rate set by the compression rate setting means by a predetermined value.
4 . An image processing apparatus as defined in claim 1 , wherein the compression rate changing means sets the new dynamic range compression rate by lowering the dynamic range compression rate set by the compression rate setting means more as the pixel number of the high saturation pixels becomes larger.
5 . An image processing apparatus as defined in claim 4 , wherein the compression rate changing means sets the new dynamic range compression rate so that the compression rate becomes gradually lower according to the pixel number of the high saturation pixels.
6 . An image processing method comprising the steps of:
obtaining a processed image of which dynamic range has been compressed by compressing a dynamic range of a color image;
setting a dynamic range compression rate for compressing the dynamic range of the color image based on the dynamic range of the color image;
calculating saturation of each of a plurality of pixels in the color image, counting a pixel number of high saturation pixels of which saturation is higher than a first threshold value, and if the pixel number is equal to or larger than a second threshold value, setting a new dynamic range compression rate which is lower than the dynamic range compression rate; and
creating a compression table based on one of the dynamic range compression rate and the new dynamic range compression rate.
7 . A program for causing a computer to execute an image processing method, the program comprising the procedures for:
obtaining a processed image of which dynamic range has been compressed by compressing a dynamic range of a color image;
setting a dynamic range compression rate for compressing the dynamic range of the color image based on the dynamic range of the color image;
calculating saturation of each of a plurality of pixels in the color image, counting a pixel number of high saturation pixels of which saturation is higher than a first threshold value, and if the pixel number is equal to or larger than a second threshold value, setting a new dynamic range compression rate which is lower than the dynamic range compression rate; and
creating a compression table based on one of the dynamic range compression rate and the new dynamic range compression rate.