密度测定法（Densitometry）是利用相纸等感光性材料来量测一物质的吸光度的技术。

浓度(Density)的意义包含以下三种：

明暗的程度、物质阻挡或吸收光线的能力、在印刷表图像受到光的照射所产生黑白深浅的程度。

Densitometry is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or photographic film, due to exposure to light. Optical density is a result of the darkness of a developed picture and can be expressed absolutely as the number of dark spots (i.e., silver grains in developed films) in a given area, but usually it is a relative value, expressed in a scale.