Tummuusasteikko

Tummuusasteikko, or grayscale, is a scale of brightness levels used to represent luminance in images orPrints without color. It describes how dark or light a pixel appears, ranging from black to white, and is commonly used when color information is unnecessary, insufficient, or undesired for analysis, reproduction, or interpretation.

In digital imaging, a tummuusasteikko is usually implemented as a one-channel gray image. The most common formats use 8-bit depth with 256 distinct levels (0 for black to 255 for white), but higher bit depths such as 12, 14, or 16 bits per pixel provide thousands to tens of thousands of levels. Some systems normalize brightness to a 0–1 range or store data in separate luminance channels for processing.

Perception and display characteristics influence the design of tummuusasteikko. Because human vision is more sensitive to mid-tones than extreme blacks and whites, gamma correction or perceptual encoding is often applied to ensure that equal steps on the scale correspond to roughly equal perceptual changes in brightness. Linear scales differ from gamma-encoded scales in how they compress or expand tonal differences.

Applications include image analysis, medical imaging, document scanning and OCR, printing, display calibration, and scientific visualization. Grayscale is also used in tonal mapping and contrast adjustment, where color information is either not available or deliberately removed to emphasize structure and texture.

Conversion from color to grayscale commonly uses luminance-based weighting, such as combining the red, green, and blue channels according to their perceived brightness (for example, weighted sums like 0.21R + 0.72G + 0.07B or similar). This reflects human sensitivity to different wavelengths and yields a visually balanced tummuusasteikko.