Density Correction Profile Generation for Inkjet Printers
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Solution Overview
Problem
Conventional methods for generating density correction profiles in image forming devices fail to smoothly connect waveforms of ink discharge characteristics, leading to unnatural density differences between pixels, which prevents adequate elimination of density unevenness in printed images due to variations in recording characteristics between recording elements.
Innovation Solution
A density correction profile generation method that involves acquiring a density profile of each pixel, extracting pixels with significant density differences, and applying filters with narrower ranges and higher peak intensities as the distance from the pixel of interest decreases, to convolute the correction profile and smooth density variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If smoothing processing is applied to the image signal to remove noise, then noise components are removed, but variations in high frequency components of density cannot be sufficiently eliminated
Solution Approach 1:
The patent segments the image signal into multiple frequency bands (low frequency band and high frequency band) and applies different processing methods to each band. Low frequency components are smoothed to remove noise, while high frequency components are processed separately to eliminate density variations, thereby resolving the contradiction between noise removal and density uniformity.
Solution Approach 2:
The patent applies different processing intensities and methods to different frequency components of the image signal. Specifically, gentle smoothing is applied to low frequency components while more aggressive processing is applied to high frequency components, allowing simultaneous noise removal and density variation elimination without compromising either aspect.
2Manufacturing precision
If density correction values are calculated from image signal with noise to correct density unevenness, then density unevenness is corrected, but unnatural density differences are generated at connection portions of frequency bands
Solution Approach 1:
The patent performs preliminary smoothing processing on the image signal before calculating density correction values. By pre-processing the signal to remove noise and smooth transitions, the subsequent density correction calculation produces more accurate results without generating unnatural density differences at connection portions.
Solution Approach 2:
The patent introduces frequency band decomposition as an intermediary step between image acquisition and density correction. This intermediary processing separates the signal into manageable frequency components, allowing independent optimization of each band and ensuring smooth transitions when recombining them for final density correction.
Data Source
AI summary
Density of each pixel is specified from a test pattern for measurement of density distribution, a density profile indicating distribution of the specified density for each pixel is acquired, and a pixel region including a “nozzle of interest” having a certain density difference or more from surrounding pixels and pixels on both sides thereof is extracted as a nozzle region of interest from the acquired density profile. Filters B to E, other than a filter A to be applied for density smoothing processing of pixels that do not belong to the nozzle region of interest, are applied for the density smoothing processing of the pixels in the nozzle region of interest, to generate a profile of a density correction value for eliminating a density difference between respective pixels based on the density profile after the smoothing processing.