Color Inspection Apparatus for Dark Objects
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Solution Overview
Problem
In color inspection using digital cameras, dark-colored objects face challenges with signal-to-noise ratio deterioration due to insufficient light, leading to inaccurate color evaluation, especially when exposure conditions are not appropriately matched for both the inspection object and reference white.
Innovation Solution
An image processing apparatus that acquires data from both the inspection object and a color chart group within the same angle of view, estimates the reference white value based on unsaturated pixel values from the color charts, and calculates color values using CIE tristimulus values to evaluate the object's color accurately, even under overexposure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If imaging is performed under appropriate exposure condition for dark-colored objects, then signal-to-noise ratio is improved, but color accuracy deteriorates due to insufficient light amount
Solution Approach 1:
The patent combines the imaging of the inspection object and reference white into a single image captured under the same exposure condition. This merging eliminates the need for separate imaging sessions and allows simultaneous acquisition of both object and reference data with consistent exposure parameters, resolving the contradiction between achieving adequate signal-to-noise ratio and maintaining color accuracy.
Solution Approach 2:
The patent changes the exposure condition parameter from being optimized for reference white (which causes underexposure of dark objects) to being optimized for the inspection object. By adjusting exposure conditions to suit dark-colored objects, the system achieves adequate signal-to-noise ratio while using the captured image to derive reference white values through image processing, thus maintaining color accuracy.
2Measurement precision
If separate imaging is performed for inspection object and reference white, then color accuracy is improved, but productivity deteriorates due to additional imaging time
Solution Approach 1:
The patent merges the imaging of inspection object and reference white into a single simultaneous capture operation. This eliminates the sequential imaging process required by conventional methods, thereby improving productivity while maintaining color accuracy through computational derivation of reference white values from the same image.
Solution Approach 2:
The patent uses the captured image of the inspection object to create a copy or derived representation of reference white information. By extracting reference white values from pixels within the same image through image processing algorithms, the system eliminates the need for separate reference white imaging, thus improving productivity without sacrificing color measurement precision.
3Measurement precision
If exposure condition is optimized for reference white, then color evaluation accuracy is improved, but signal-to-noise ratio deteriorates for dark-colored objects
Solution Approach 1:
The patent changes the exposure condition parameter optimization target from reference white to the inspection object. By setting exposure conditions appropriate for capturing dark-colored objects with adequate signal-to-noise ratio, the system achieves reliable object imaging while using image processing techniques to derive accurate reference white values from the same exposure conditions.
Solution Approach 2:
The patent creates a derived copy of reference white information from the inspection object image itself. Through image processing algorithms that analyze pixel values within the captured image, the system reconstructs reference white values that correspond to the actual exposure conditions used, thereby maintaining color evaluation accuracy even when exposure is optimized for dark objects rather than reference white.
Data Source
AI summary
An apparatus for evaluating color of an object includes an acquisition unit configured to acquire image data which is acquired by imaging the object and a color chart group including color charts having different reflectance within a one angle of view, an estimation unit configured to estimate a value of reference white under an exposure condition corresponding to the imaging based on the image data, and a calculation unit configured to calculate a color value for evaluating the color of the object based on the image data and the estimated value of the reference white.