Image forming device, image forming method, and recording medium that provide multi-level error diffusion
First Claim
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1. An image forming device in which each pixel of an M-level gradation input image is quantized into one of N levels (M>
- N≧
2) through an error diffusion process, comprising;
a threshold determination unit determining a threshold value according to a gradation value of a target pixel of the M-level gradation input image before quantization;
a specific concentration determination unit determining whether the gradation value of the target pixel is equal to a specific concentration which indicates one of the N levels after quantization;
a mask addition unit adding a mask noise value to the gradation value of the target pixel when the gradation value of the target pixel is equal to the specific concentration before quantization, wherein the mask noise value is determined according to a position of the target pixel; and
a quantization unit performing the quantization through the error diffusion process by using the threshold value and the gradation value of the target pixel to which the mask noise value is added.
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Abstract
An image forming device includes a quantization unit which quantizes each pixel of an M-level gradation input image into one of N levels (M>N≧2) through an error diffusion process. An operation unit performs a predetermined operation according to a position of a target pixel to a gradation value of the target pixel before quantization when the gradation value of the target pixel is equal to a specific concentration.
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Citations
7 Claims
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1. An image forming device in which each pixel of an M-level gradation input image is quantized into one of N levels (M>
- N≧
2) through an error diffusion process, comprising;a threshold determination unit determining a threshold value according to a gradation value of a target pixel of the M-level gradation input image before quantization; a specific concentration determination unit determining whether the gradation value of the target pixel is equal to a specific concentration which indicates one of the N levels after quantization; a mask addition unit adding a mask noise value to the gradation value of the target pixel when the gradation value of the target pixel is equal to the specific concentration before quantization, wherein the mask noise value is determined according to a position of the target pixel; and a quantization unit performing the quantization through the error diffusion process by using the threshold value and the gradation value of the target pixel to which the mask noise value is added. - View Dependent Claims (2, 3, 4, 5)
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6. An image forming method in which each pixel of an M-level gradation input image is quantized into one of N levels (M>
- N≧
2) through an error diffusion process, comprising the steps of;determining a threshold value according to a gradation value of a target pixel of the M-level gradation input image before quantization; determining whether the gradation value of the target pixel is equal to a specific concentration which indicates one of the N levels after quantization; determining, before quantization, a mask noise value according to a position of the target pixel and adding the determined mask noise value to the gradation value of the target pixel when the gradation value of the target pixel is equal to the specific concentration; and performing the quantization through the error diffusion process by using the threshold value and the gradation value of the target pixel to which the mask noise value is added.
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7. A computer-readable storage medium storing a computer program embodied therein for causing a computer to execute an image forming method in which each pixel of an M-level gradation input image is quantized into one of N levels (M>
- N≧
2) through an error diffusion process, the method comprising the steps of;determining a threshold value according to a gradation value of a target pixel of the M-level gradation input image before quantization; determining whether the gradation value of the target pixel is equal to a specific concentration which indicates one of the N levels after quantization; determining, before quantization, a mask noise value according to a position of the target pixel and adding the determined mask noise value to the gradation value of the target pixel when the gradation value of the target pixel is equal to the specific concentration; and performing the quantization through the error diffusion process by using the threshold value and the gradation value of the target pixel to which the mask noise value is added.
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Specification