What is thresholding?

Question

Options

• Athe conversion of a multi-bit grayscale image into a multicolor image
• Bthe conversion of a multi-bit grayscale image into a black and white image
• Cthe conversion of a multicolor image into a black and white image
• Dthe conversion of a black and white image into a multi-bit grayscale image

• A
  93% (43)
• C
  2% (1)
• D
  4% (2)

Explanation

There appears to be an error in the provided answer key - B is the correct answer, not A.

Thresholding is the process of converting a multi-bit grayscale image into a binary (black and white) image by selecting a cutoff value: pixels above the threshold become white, pixels below become black. This is one of the most fundamental operations in image processing and computer vision.

• A is wrong - converting grayscale to multicolor describes a colorization or false-color mapping operation, not thresholding.
• C is wrong - thresholding specifically starts from a grayscale image (with intensity values), not a multicolor/RGB image. Converting color directly to B&W is color-to-grayscale conversion plus possibly thresholding, but that's not the standard definition.
• D is wrong - this describes the opposite direction: going from binary to grayscale, which would be an expansion of bit depth, not reduction.

Memory tip: Think of a threshold as a fence - everything on one side goes white, the other goes black. The input must be grayscale (multi-bit intensity values) because you need a numeric value to compare against the threshold. No numeric intensity = no threshold comparison.

If your exam materials mark A as correct, I'd recommend flagging it with your instructor - this conflicts with the standard definition used across image processing textbooks and curricula.

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