Hue map generation for highlight recovery

A method, comprising:

• determining filter coefficients for each pixel in a first image at a first resolution lower than a resolution of the input image and captured within a threshold time interval from capturing the input image, using differences between pixel values of the first image and other pixel values of a second image for each color channel of a plurality of color channels in a patch surrounding each pixel, the second image at the first resolution having the plurality of color channels;
• filtering the pixel values of the first image for each color channel using the filter coefficients for each pixel to generate a filtered image having the plurality of color channels;
• determining a hue for each color channel for each pixel in the filtered image, using a corresponding pixel value for each color channel and corresponding pixel values for the plurality of color channels in the filtered image;
• determining a plurality of weights for the plurality of color channels for each pixel in the filtered image, based on hues for each pixel for the plurality of color channels and the corresponding pixel values;
• and
• generating a plurality of candidate hue maps at the first resolution for the plurality of color channels, based on the weights for each pixel and pixel values in the filtered image in a patch surrounding each pixel for the plurality of color channels.

An electronic device, comprising:

• an image sensor configured to:
• capture a first image at a first resolution comprising a pixel with hue information having a clipped color channel, and
• capture a second image at a second resolution lower than the first resolution and having a plurality of color channels, the second image captured at an exposure level lower than an exposure level of the first image and within a threshold time interval from capturing the first image;
• and
• an image signal processor coupled to the image sensor, the image signal processor configured to perform raw processing of the first image to obtain a raw processed version of the first image having the plurality of color channels, the image signal processor including:
• a filter circuit configured to:
• determine filter coefficients for each pixel in the second image, using differences between pixel values of the second image and other pixel values of a third image for each color channel in a patch surrounding each pixel, the third image at the second resolution having the plurality of color channels, and
• filter the pixel values of the second image for each color channel using the filter coefficients for each pixel to generate a filtered image having the plurality of color channels;
• and
• a hue map generator circuit configured to:
• determine a hue for each color channel for each pixel in the filtered image, using a corresponding pixel value for each color channel and corresponding pixel values for the plurality of color channels in the filtered image,
• determine a plurality of weights for the plurality of color channels for each pixel in the filtered image, based on hues for each pixel for the plurality of color channels and the corresponding pixel values, and
• generate a plurality of candidate hue maps at the second resolution for the plurality of color channels, based on the weights for each pixel and pixel values in the filtered image in a patch surrounding each pixel for the plurality of color channels.