Image processing apparatus and method, program, and recording medium

1. An image processing apparatus comprising:

computation means for determining an interpolation process starting point and an interpolation process gradient by

comparing, when an image signal has a change point at which a difference between pixels values of adjacent pixels of the image signal is greater than zero and is less than or equal to a predetermined threshold value, a first continuous width of identical grayscale value pixels scanned earlier than the change point with a second continuous width of identical grayscale value pixels scanned later than the change point to determine a comparison result,

when the comparison result is the first continuous width is smaller than the second continuous width, a position of a pixel scanned earlier by substantially one-half the first continuous width than the change point as the interpolation process starting point, and determining the interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the first continuous width, and

setting, when the comparison result is the first continuous width is greater than the second continuous width, a position of a pixel scanned earlier by substantially one-half the second continuous width than the change point as the interpolation process starting point, and determining the interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the second continuous width; and

conversion means for converting pixel grayscale values of the image signal on the basis of the interpolation process starting point and interpolation process gradient determined by the computation means so that a grayscale change from the interpolation process starting point in the image signal has a value in accordance with the interpolation process gradient.

2. The image processing apparatus according to claim 1 , wherein the image signal is a converted image signal obtained by converting an N-bit image signal into an M-bit image signal.

3. The image processing apparatus according to claim 2 , wherein the predetermined threshold value is equal to a value represented by an (M−N)-th power of 2.

4. The image processing apparatus according to claim 1 , further comprising horizontal-component noise removing means for removing a noise component in a horizontal direction of the image signal,

wherein the computation means executes a computation process on the basis of the image signal in which the noise component in the horizontal direction has been removed by the horizontal-component noise removing means.

5. The image processing apparatus according to claim 1 , further comprising vertical-component noise removing means for removing a noise component in a vertical direction of the image signal,

wherein the computation means executes a computation process on the basis of the image signal in which the noise component in the vertical direction has been removed by the vertical-component noise removing means.

6. The image processing apparatus according to claim 1 , further comprising two data storage means each capable of storing computation results for every horizontal line which are obtained by the computation means,

wherein the computation means and the conversion means execute processing of the image signal for every horizontal line, and

wherein when one of the two data storage means is recording computation results obtained by the computation means, the conversion means converts pixel values of the image signal using computation results for a preceding horizontal line which are obtained by the computation means and which are stored in the other data storage means.

7. An image processing method for an image processing apparatus that executes image processing to provide display of an image signal, comprising the steps of:

obtaining an image signal;

determining whether or not the image signal has a change point at which a difference between pixel values of adjacent pixels of the image signal is greater than zero and is less than or equal to a predetermined threshold value;

comparing, when the image signal has the change point, a first continuous width of identical grayscale value pixels scanned earlier than the change point with a second continuous width of identical grayscale value pixels scanned later than the change point to determine a comparison result;

when the comparison result is the first continuous width is smaller than the second continuous width, a position of a pixel scanned earlier by substantially one-half the first continuous width than the change point as an interpolation process starting point, and determining an interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the first continuous width;

setting, when the comparison result is the first continuous width is greater than the second continuous width, a position of a pixel scanned earlier by substantially one-half the second continuous width than the change point as an interpolation process starting point, and determining an interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the second continuous width; and

converting pixel grayscale values of the image signal on the basis of the obtained interpolation process starting point and interpolation process gradient so that a grayscale change from the interpolation process starting point in the image signal has a value in accordance with the interpolation process gradient.

8. A non-transitory storage medium on which is recorded a computer readable program for causing a computer to execute image processing to provide display of an image signal, the program causing the computer to execute a process comprising the steps of:

obtaining an image signal;

determining whether or not the image signal has a change point at which a difference between pixel values of adjacent pixels of the image signal is greater than zero and is less than or equal to a predetermined threshold value;

comparing, when the image signal has the change point, a first continuous width of identical grayscale value pixels scanned earlier than the change point with a second continuous width of identical grayscale value pixels scanned later than the change point to determine a comparison result;

when the comparison result is the first continuous width is smaller than the second continuous width, a position of a pixel scanned earlier by substantially one-half the first continuous width than the change point as an interpolation process starting point, and determining an interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the first continuous width;

setting, when the comparison result is the first continuous width is greater than the second continuous width, a position of a pixel scanned earlier by substantially one-half the second continuous width than the change point as an interpolation process starting point, and determining an interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the second continuous width; and

converting pixel grayscale values of the image signal on the basis of the obtained interpolation process starting point and interpolation process gradient so that a grayscale change from the interpolation process starting point in the image signal has a value in accordance with the interpolation process gradient.

9. An image processing apparatus comprising:

a computation unit configured to determine an interpolation process starting point and an interpolation process gradient by

comparing, when an image signal has a change point at which a difference between pixel values of adjacent pixels of the image signal is greater than zero and is less than or equal to a predetermined threshold value, a first continuous width of identical grayscale value pixels scanned earlier than the change point with a second continuous width of identical grayscale value pixels scanned later than the change point to determine a comparison result,

when the comparison result is the first continuous width is smaller than the second continuous width, a position of a pixel scanned earlier by substantially one-half the first continuous width than the change point as the interpolation process starting point, and determining the interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the first continuous width, and

setting, when the comparison result is the first continuous width is greater than the second continuous width, a position of a pixel scanned earlier by substantially one-half the second continuous width than the change point as the interpolation process starting point, and determining the interpolation process gradient on the basis of a difference between pixel grayscale values before and after the change point and the second continuous width; and

a conversion unit configured to convert pixel grayscale values of the image signal on the basis of the interpolation process starting point and interpolation process gradient determined by the computation unit so that a grayscale change from the interpolation process starting point in the image signal has a value in accordance with the interpolation process gradient.