Halftone Image Uniformity Compensation via Spatial TRC
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Solution Overview
Problem
Image rendering systems face non-uniformities due to variations in spot size, LED efficiency, lens imperfections, and photoreceptor imperfections, leading to artifacts like streaks and banding, especially when image data is in a halftoned format, limiting the effectiveness of compensating Tone Reproduction Curves.
Innovation Solution
A method involving the predetermination of spatially dependent compensating Tone Reproduction Curves, using mathematical basis decomposition to generate basis vectors and weights, and applying error diffusion to determine compensated values for halftone pixels, effectively addressing non-uniformities in image rendering devices even with halftoned image data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Tone Reproduction Curves are used to compensate for rendering device non-uniformities, then image uniformity is improved, but the method is ineffective for halftoned image data
Solution Approach 1:
The patent applies local quality by creating position-dependent compensating curves for different spatial locations in the image. Instead of using a single global TRC, the system generates multiple TRCs tailored to specific regions, allowing each location to be compensated according to its unique non-uniformity characteristics. This enables effective compensation for halftoned images by adapting the compensation strategy to local image properties and spatial positions.
2Manufacturing precision
If system components are manufactured to higher tolerances to improve image uniformity, then rendering quality is improved, but design and production costs increase
Solution Approach 1:
The patent applies preliminary action by measuring and characterizing rendering device non-uniformities before actual image rendering. The system performs calibration measurements to determine position-dependent compensating curves in advance, storing these characteristics for later use. This allows the rendering device to operate with standard tolerances while still achieving high uniformity through pre-computed compensation applied during normal operation, avoiding the need for expensive high-precision manufacturing.
3Manufacturing precision
If spatially dependent compensating curves are applied to halftoned images, then image uniformity is improved, but computational complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the image space into multiple positions or regions, each with its own compensating TRC. The system processes halftoned images by applying the appropriate position-dependent curve to each pixel or small group of pixels based on its spatial location. This segmentation approach enables uniformity compensation for halftoned data while managing computational complexity through efficient lookup and application of pre-computed position-specific curves.
Data Source
AI summary
Compensation for rendering device non-uniformities is provided for halftoned images. A spatially dependent tone reproduction curve (TRC) provides compensation values. Pixel location information is used to access TRC values. For example, the values are modification values. The modification values are added to the pixel values to generate combined values. Quantization is applied to the combined values to prepare compensated image data for rendering. For example, Rank Ordered Error Diffusion is applied to the combined values. The combined values may include diffused error from previously processed pixels. Gray values may be estimated for the respective pixels. The estimated gray values may be used to access compensation information from a TRC that is both spatially and gray value dependent. Mathematical basis decomposition is used to reduce TRC memory requirements. For example, Discrete Cosine Transformation, Singular Value Decomposition or Principal Component Analysis is used to determine a compact form for the TRC.