Logpx

Logpx is a unitless metric used in digital imaging to represent pixel brightness on a logarithmic scale. It is designed to align with the way human vision perceives light, which is more sensitive to relative than absolute changes in intensity. In its common form, logpx is defined as logpx = log10(I / I0), where I is the linear pixel intensity and I0 is a reference intensity, often the minimum detectable level or white. When I can be zero, a small epsilon is added to avoid taking a logarithm of zero.

Logpx is used in image processing and visualization to achieve dynamic range compression and more perceptually uniform representations. It appears in workflows such as tone mapping for high dynamic range (HDR) images, contrast enhancement, and histogram-based operations where linear brightness values would obscure detail in either shadows or highlights.

Variations of logpx may involve normalization or scaling for storage or display, for example rescaling to a 0–1 range or to 0–255. Some pipelines compute logpx from radiance or irradiance rather than raw sensor values, and they may apply offsets or baselines to ensure all values fall within a usable range.

Edge cases include zero or near-zero intensity, which require safeguards like epsilon and careful handling to avoid negative infinity. See also logarithmic scales, pixel intensity, HDR imaging, and tone mapping.