Patent ID: 7440139
Filing Date: 2008-10-21
Classification: H04N

Abstract:
1. A method for controlling a tone reproduction curve of a halftone digital image, the method comprising: receiving the halftone digital image; selecting a target pixel and a neighborhood area of the selected target pixel; estimating a local gray value of the selected target pixel and the selected neighborhood area; determining a modification value for the selected target pixel based on a relationship between the estimated local gray value and a desired gray level; modifying a pixel value of the selected target pixel using the determined modification value; determining a quantization error for the selected target pixel, wherein when the determined quantization error is not equal to zero, the method further comprising: selecting a diffusion mask, the mask relating to the target pixel and pixels neighboring thereto; diffusing the determined quantization error using a rank-ordered error diffusion to at least one pixel based on the selected diffusion mask, the rank-order error diffusion acting on only four pixels of the neighboring area and comprising: performing a blurring operation about neighboring pixels prior to performing rank-order error diffusion when the received halftone digital image is a binary image.