RGBW Image Signal Processor
Our RGBW processor provides front-end ISP functionality, including demosaicking and fusion of W with RGB to increase the latter’s SNR. It has a flexible framework that supports all RGBW CFA patterns manufactured to date, requiring only a change of filter coefficients for different CFA patterns. Our processor is hardware-friendly and has already been implemented in silicon.
Our demosaicking quality is excellent, surpassing that of most high-end Bayer demosaickers, with high luminance and chrominance resolution and minimal aliasing and moire. In addition, our joint demosaicking and chromatic aberration correction deliver better quality than the standard method of performing the two operations separately.
We demosaick both a RGB image and a W color plane, with the latter being used to clean up the former through a fusion process similar to chroma denoising. The SNR lead over Bayer depends on the specific RGBW CFA employed. In low-light, read noise-limited conditions, the SNR lead ranges from 4 dB for the double-binnable Quad-RGBW CFA to 6.5 dB for the non-binnable RGBW-Canon CFA.
|6.5 dB||3.25 dB|
|RGBW-Kodak||Mobile Phone||6 dB||3 dB|
|RGBW-IA||Mobile Phone||6 dB||3 dB|
|RGBW-QuadIA||Mobile Phone||4 dB||2 dB|
|RGBW-Hexadeca||Mobile Phone||6 dB||3 dB|
The SNR improvement provided by RGBW is due to the greater sensitivity of W pixels compared to RGB pixels on gray image features. On saturated red, green, and blue image features, the R, G, and B pixels respectively are almost as sensitive as W pixels. However, the higher density of pixels sensitive to the color in question gives RGBW its SNR advantage. For instance, both W and R pixels are sensitive to saturated reds, accounting for 5/8 of all RGBW pixels, whereas only 1/4 of Bayer pixels are sensitive to red.
The dynamic range extension provided by RGBW depends on the degree of W overexposure. For more details, please see our White Pixel HDR page. In conventional sensors where all pixels are exposed equally, the dynamic range extension equals the SNR lead and ranges from 4 dB on the double binnable Quad-RGBW CFA to 6.5 dB on the non-binnable RGBW-Canon CFA.