Halftone Image Dot Placement Using Precomputed Low-Pass Filter Lookup Tables
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Solution Overview
Problem
The conventional Direct Binary Search (DBS) method for generating halftone images requires a significant amount of arithmetic operations due to the need for repeated dot displacement and correction processing for each focused dot, which is inefficient in optimizing dot arrangement for high-quality halftone images.
Innovation Solution
An image processing device and method that generates a first and second low-pass image, calculates their difference, and uses this difference to determine the optimal dot placement pixel, allowing for dot displacement and updating the halftone image arrangement with reduced arithmetic operations by specifying the dot placement pixel based on pixel value comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the conventional DBS method is used to generate halftone images by repeatedly displacing focused dots and applying low-pass filters, then high-quality halftone images with optimized dot arrangement are obtained, but a significant amount of arithmetic operations are required
Solution Approach 1:
The patent pre-calculates and stores the low-pass filter responses for all possible dot positions in a lookup table before the main halftone generation process. This preliminary action eliminates the need for repeated low-pass filter applications during the iterative dot displacement process, significantly reducing arithmetic operations while maintaining image quality
Solution Approach 2:
The patent uses a difference image that copies and subtracts the low-pass filtered halftone image from the low-pass filtered input image to identify error locations. This copying approach allows efficient error detection without re-processing the original images, reducing computational burden
2Manufacturing precision
If repeated dot displacement and low-pass filter application are performed for each focused dot, then optimal dot placement is achieved, but processing time increases significantly
Solution Approach 1:
The low-pass filter responses are pre-computed and stored in advance, so during the actual dot displacement iterations, the system only needs to retrieve and combine pre-computed values rather than applying filters repeatedly, thus reducing processing time
Solution Approach 2:
The patent applies the low-pass filter only to the specific region affected by each dot displacement rather than to the entire image, reducing the computational workload while still achieving sufficient optimization of the local dot arrangement
Data Source
AI summary
An image processing device includes a first image generation unit which generates a first image obtained by applying a first low-pass filter to an input image, a second image generation unit which generates a second image obtained by applying a second low-pass filter to a halftone image, a third image generation unit which generates a third image representing a difference between the first image and the second image, a focused dot setting unit which sets a focused dot, a dot placement pixel determination unit which compares pixel values in the third image and determining a dot placement pixel for improving the uniformity of the gradation distribution in the third image, and a dot displacing unit which displaces the focused dot to the dot placement pixel and updates the halftone image.