Phantom level edge enhanced error diffusion

Claim 1

A method for converting an input image including a plurality of input pixels each having a first number of possible input levels of optical density to an output image including a plurality of output pixels each having a second number of possible output levels of optical density, a set of output levels corresponding to an operative range of an output device, comprising: generating a modified optical density value by adding an error value, if any, to the input level of one of the input pixels; generating a phantom output level as a function of the modified optical density level, the phantom output level corresponding to an output level beyond the operative range of the output device; determining the error value as a function of the selected phantom output level; and generating an output pixel having one of the output levels determined as a function of the modified optical density value.

Claim 2

A method for converting an input image including a plurality of input pixels each having a first number of possible input levels of optical density to an output image including a plurality of output pixels each having a second number of possible output levels of optical density, a set of output levels corresponding to an operative range of an output device, comprising: generating a modified optical density value by adding an error value, if any, to the input level of one of the input pixels; generating a phantom output level as a function of the modified optical density level, the phantom output level corresponding to an output level beyond the operative range of the output device; determining the error value as a function of the selected phantom output level; and generating an output pixel having one of the output levels determined as a function of the modified optical density value.

Claim 10

A method for converting an input image including a plurality of input pixels each having a first number of possible input levels of optical density to an output image including a plurality of output pixels each having a second number of possible output levels of optical density, comprising: generating a modified optical density value by adding an error value if any, to the input level of one of the input pixels; generating a phantom output level as a function of the modified optical density level; determining the error value as a function of the selected phantom output level; and generating an output pixel having one of the output levels determined as a function of the modified optical density value, wherein said generating step comprises generating the phantom output level by comparing the modified optical density value to a clipping level, generating the clipping level to be greater than the largest of the m possible input levels of optical density or less than the smallest of the m input levels of optical density, and generating the phantom output level to be greater than the selected clipping level which is greater than the largest of the m possible input levels of optical density.

Claim 11

A method for converting an input image including a plurality of input pixels each having a first number of possible input levels of optical density to an output image including a plurality of output pixels each having a second number of possible output levels of optical density, comprising: generating a modified optical density value by adding an error value if any, to the input level of one of the input pixels; generating a phantom output level as a function of the modified optical density level; determining the error value as a function of the selected phantom output level; and generating an output pixel having one of the output levels determined as a function of the modified optical density value, wherein said generating step comprises generating the phantom output level by comparing the modified optical density value to a clipping level, generating the clipping level to be greater than the largest of the m possible input levels of optical density or less than the smallest of the m input levels of optical density, and generating the phantom output level to be greater than the selected clipping level which is greater than the largest of the m possible input levels of optical density.

Claim 17

A method of quantizing pixel values in an image formed by a plurality of pixels, each pixel representing an optical density of the image at a location therein, and having an original optical density value associated therewith selected from one of a set of original optical density values, having a number of members n larger than a desired output set of optical density values, the output set of optical density values corresponding to an operative range of an output device, comprising: adding to an original density value of each pixel, an error signal resulting from quantization of previous pixels, if any, to derive a modified density value; determining an error term as a function of the difference between a phantom output level value and the modified density value, the phantom output level value corresponding to an output optical density value beyond the operative range of the output device; and comparing the modified density value of a pixel with a threshold value to select an output value representing the pixel from a set of m possible density values.

Claim 18

A method of quantizing pixel values in an image formed by a plurality of pixels, each pixel representing an optical density of the image at a location therein, and having an original optical density value associated therewith selected from one of a set of original optical density values, having a number of members n larger than a desired output set of optical density values, the output set of optical density values corresponding to an operative range of an output device, comprising: adding to an original density value of each pixel, an error signal resulting from quantization of previous pixels, if any, to derive a modified density value; determining an error term as a function of the difference between a phantom output level value and the modified density value, the phantom output level value corresponding to an output optical density value beyond the operative range of the output device; and comparing the modified density value of a pixel with a threshold value to select an output value representing the pixel from a set of m possible density values.

Claim 22

A method of quantizing pixel values in an image is formed by a plurality of pixels, each pixel representing an optical density of the image at a location therein, and having an original optical density value associated therewith selected from one of a set of original optical density values, having a number of members n larger than a desired output set of optical density values, comprising: adding to an original density value of each pixel, an error signal resulting from quantization of previous pixels, if any, to derive a modified density value; determining an error term as a function of the difference between a phantom output level value and the modified density value wherein said step comprises determining the phantom output level by comparing the modified optical density value to a clipping level, determining the clipping level to be greater than the largest of the m possible input levels of optical density or less than the smallest of the m input levels of optical density, and determining the phantom output level to be greater than the determined clipping level which is greater than the largest of the m possible input levels of optical density; and comparing the modified density value of a pixel with a threshold value to select an output value representing the pixel from a set of m possible density values.

Claim 23

A method of quantizing pixel values in an image is formed by a plurality of pixels, each pixel representing an optical density of the image at a location therein, and having an original optical density value associated therewith selected from one of a set of original optical density values, having a number of members n larger than a desired output set of optical density values, comprising: adding to an original density value of each pixel, an error signal resulting from quantization of previous pixels, if any, to derive a modified density value; determining an error term as a function of the difference between a phantom output level value and the modified density value wherein said step comprises determining the phantom output level by comparing the modified optical density value to a clipping level, determining the clipping level to be greater than the largest of the m possible input levels of optical density or less than the smallest of the m input levels of optical density, and determining the phantom output level to be greater than the determined clipping level which is greater than the largest of the m possible input levels of optical density; and comparing the modified density value of a pixel with a threshold value to select an output value representing the pixel from a set of m possible density values.