gbc {rcaiman}

Gamma back correction

Description

Gamma back correction of JPEG images

Usage

gbc(DN_from_JPEG, gamma = 2.2)

Arguments

DN_from_JPEG

Numeric vector or object of the SpatRaster class. Digital numbers from a JPEG file (0 to 255, i.e., the standard 8-bit encoded).

gamma

Numeric vector of length one. Gamma value. Please see Díaz and Lencinas (2018) for details.

Details

Digital cameras usually use sRGB as color space. It is a standard developed to ensure accurate color and tone management. The transfer function of sRGB, known as gamma correction, is very close to a power function with the exponent 1/2.2. This is why a DN of a born-digital photograph that was encoded in sRGB has a non-linear relationship with luminance despite having the sensor a linear response.

Value

The same class as DN_from_JPEG, with dimension unchanged but values rescaled between 0 and 1 in a non-linear fashion.

References

Díaz GM, Lencinas JD (2018). “Model-based local thresholding for canopy hemispherical photography.” Canadian Journal of Forest Research, 48(10), 1204–1216. doi:10.1139/cjfr-2018-0006.

See Also

Other Pre-processing Functions: enhance_caim(), local_fuzzy_thresholding(), membership_to_color(), normalize()

Examples

path <- system.file("external/DSCN4500.JPG", package = "rcaiman")
r <- read_caim(path, c(1250, 1020) - 745, 745 * 2, 745 * 2)
r
gbc(r)