Applies a fixed-level threshold to each array element

dst = cv.threshold(src, thresh)
dst = cv.threshold(src, thresh, 'OptionName',optionValue, ...)
[dst, thresh] = cv.threshold(src, 'auto', ...)

Input

• src Input array (single-channel, 8-bit, 16-bit, or 32-bit floating point).
• thresh Threshold value. Scalar numeric value or one of the strings:
  • Otsu use Otsu algorithm to choose the optimal threshold value
  • Triangle use Triangle algorithm to choose the optimal threshold value

Output

• dst Output array of the same size and type as src.
• thresh Threshold value used.

Options

• MaxValue Maximum value to use with the 'Binary' and 'BinaryInv' thresholding types. default 255
• Type Thresholding type, default 'Binary'. One of:
  • Binary dst(x,y) = (src(x,y) > thresh) ? maxVal : 0
  • BinaryInv dst(x,y) = (src(x,y) > thresh) ? 0 : maxVal
  • Trunc dst(x,y) = (src(x,y) > thresh) ? thresh : src(x,y)
  • ToZero dst(x,y) = (src(x,y) > thresh) ? src(x,y) : 0
  • ToZeroInv dst(x,y) = (src(x,y) > thresh) ? 0 : src(x,y)

The function applies fixed-level thresholding to a single-channel array. The function is typically used to get a bi-level (binary) image out of a grayscale image (cv.compare could be also used for this purpose) or for removing a noise, that is, filtering out pixels with too small or too large values. There are several types of thresholding supported by the function. They are determined by Type parameter.

When thresh is set 'Otsu' or 'Triangle', the function determines the optimal threshold value using the Otsu's or Triangle algorithm. The function returns the computed threshold value. Currently, the Otsu's and Triangle methods are implemented only for 8-bit images.