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Color image processing for digital cameras
Published in Sharma Gaurav, Digital Color Imaging Handbook, 2017
As a first step in providing good color reproduction, most digital cameras include a white balance operation. White balance requires adjusting the RGB signal levels provided by the image sensor to correct for the color temperature of the light source used to illuminate the scene. The amounts of red and blue light in daylight sources are approximately equal. However, many artificial light sources, such as tungsten light bulbs, provide a much higher proportion of red light than blue light. Images taken using these illuminants must have the blue signal amplified to prevent white objects from appearing unnaturally yellow in the reproduced image. This signal adjustment can occur in three different ways: 1. Using an optical color correction filter to equalize the sensor exposure levels2. Increasing the analog gain when the low signal color values are read out of the sensor3. Adjusting the digital code values of the captured image
Evaluation of Image Quality
Published in Junichi Nakamura, Image Sensors and Signal Processing for Digital Still Cameras, 2017
If white balance is lost, colors are not recorded accurately and color reproduction image quality will be compromised. Basic performance of white balance can be measured by photographing an achromatic subject such as a uniform white chart and then evaluating the chromaticity of the recorded image. If the recorded image signal is not white, the white balance of the imaging system has a problem. However, when pictures are actually taken, subjects usually have various colored patterns. Although realistic scenes are more representative of actual camera usage, it is very difficult to make a generalized decision about the patterns and light sources to use for such tests. Currently, no standard evaluation method in this meaning has been established. Thus, the typical methods for evaluating white balance performance are based on qualitative assessments of actual photographs.
Establishing Integrity of Digital Images for Court
Published in Brian E. Dalrymple, E. Jill Smith, Forensic Digital Image Processing, 2018
Brian E. Dalrymple, E. Jill Smith
Basic camera control adjustments may be adjusted in the order that they are listed in the panel. White balance refers to color temperature, describing the warmth or coolness of the image lighting. This setting defaults to “As Shot”, but you may click the drop-down arrow to specifically describe the lighting conditions for an image: auto, daylight, cloudy, shade, tungsten, fluorescent, flash, and custom. As soon as the temperature and/or tint sliders are manually adjusted, the color balance changes to “custom.” Image color balance may be achieved if there is something in the image that is known to be a neutral black, gray, or white by selecting the white balance tool (gray eyedropper) and clicking in the neutral area.
An algorithm for online detection of colour differences in warp knitted fabrics
Published in The Journal of The Textile Institute, 2022
Guosheng Xie, Yang Xu, Zhiqi Yu, Yize Sun
The reasons for the uneven brightness of the image are mainly caused by two aspects. Firstly, lighting the D65 light source on the surface of the warp knitted fabric by using the tunnel light source will cause the image to have a uniform radiance in the middle and low radiance on both sides. Secondly, the line scan camera manufacturing characteristics lead to the phenomenon of low edge brightness in the warp knitted cloth images collected. Therefore, the white balance and color correction algorithms need to be used to preprocess the warp knitted fabric images collected.