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Hot Spots and RGB Color Channels

The appearance of hot spots can be greatly influenced by how the image is post-processed. Hot spots usually are 80% in the blue channel, and so can be dealt with fairly easily by not using the blue channel or converting to grayscale or using Lightness. Shown below are the various channels; the central hot spot is quite obvious in the RGB and blue-channel images, but barely visible in the grayscale, Lightness, red, and green channels. This is your ticket to salvaging a problem image.

Below is another example of a blue channel hot spot, this time from the Canon EF 70-200mm f/4L IS USM. It’s very disappointing to see a newly-introduced lens (late 2006) show such strong hot spot problems. Mouse over/out of the image to see the red vs blue channels.

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Diglloyd Infrared Photography covers cameras and lenses for infrared photography.

The coverage explains all the issues involved in shooting in infrared, which do not change. It is not a review of any particular camera or lens, though many examples are included.

  • Guidance on workflow for infrared, including black and white and channel swapping for false-color images.
  • How infrared renders, and why certain spectral cutoffs matter: false color vs black and white.
  • Image quality issues to be on the lookout for in infrared.
  • Numerous lens evaluations in infrared.

View an overview of infrared as well as filter spectral transmission plus examples from an optimal lens.

Variants blue, red available in full article

Canon 5D-IR + Canon EF 70-200 f/4L IS USM @ f/16, blue channel
mouse over image to see the red channel

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