Distinctness of image

Distinctness of image (DOI) is a quantification of the deviation of the direction of light propagation from the regular direction by scattering during transmission or reflection. DOI is sensitive to even subtle scattering effects; the more light is being scattered out of the regular direction the more the initially sharp (well defined) image is blurred (that is, small details are lost). In polluted air it is the sum of all particles of various dimensions (dust, aerosols, vapor, etc.) that induces haze.[1]

The blur induced by a scattering layer (here: frosted glass) increases with the distance between the information (ruler scaling) and the scattering layer. The scattering layer is close to the ruler surface on the left side and the distance increases to the right as does the blur. The distinctness of image decreases with increasing blur.

Distinctness of Image (DOI) Low DOI is caused by “large” surface structures distorting the reflected light. The surface is visible- orange peel. ${\displaystyle DOI\varpropto dR/d\Theta }$ ${\displaystyle DOI\propto {\frac {\Delta Reflectance}{\Delta Angle}}}$

Reflected image Quality (RIQ)

RIQ is a more sensitive, updated version of DOI ${\displaystyle DOI\varpropto dR/d\Theta }$
${\displaystyle Haze\propto {\frac {\Delta Reflectance}{\Delta Angle}}}$ A new high sensitivity/high resolution sensor allows improved measurement.

DOI is measured to characterize the visual appearance of polished high-gloss surfaces such as automotive car finishes, mirrors, beyond the capabilities of gloss.

Other appearance phenomena are: gloss, haze, and orange peel.