Colour film Subtactive colour mixing Three layers in the film: –blue sensitve: yellow layer –green sensitive: magenta layer –red sensitive: cyan layer Silver halid + colour coplers + pigments Negativ film - colour reversal: slides

Structure of a colour film

Colour picture development

Spectral characteristics of pigments Lambert-Beer law: – : absorption coefficient – l : layer thickness – d : concentration – 1 ( ) = e - ( )× l transmission at unit thickness

Spectral transmission of pigments

Optical density D = - log ( D Spectral density: D( )= -log( ( ) ) = = -log[exp(- ( ). d.l )] = ( ). d.l D 1 ( ) = ( ). d(1).l, density at unit conc. D( ) = d. D 1 ( )

Total transmittance Transmittance: Y M C Density: D DY DM DC = d Y DY d M DM d C DC Units: d Y = d M = d C = 1 gray equiv. conc.

Colour densities of a positive film

Colours produced

Chromaticity Film - EBU comparison: 9,7

Spectral sensitivity of film - 1 Positiv film, sensitivity maxima should be there where main density/side density maximal. 9,9

Spectral sensitivity of film - 2 Typical negative film (daylight - incandescent light film): 9,10

Effect of sp. sensitivity on exp. If sp. maxima of the three sensitivities differ more, larger exp. differences occure

Exposition, negative film Exposition: H = E. t log (H) - D: 9.12 Gradation ( ): D n = C + log (H/H 0 ) D n = D n0 - D v D v : Density of object

D - D diagram of negativ film

H-D diagram of revers.film

D-D diagram of revers.film D u = D u0 +. D v, where – D u density of revers.film – D v density of target

Combined photo techniques Negative-positive technique –Negative film has low gamma –Positive film has high gamma

Masking Compensation for side densities –Produce from same target pos. + neg. image Pos.: D p = p × D v ; Neg.: D n = D n0 - n × D v ; –Combining the two: D k = D n + D p = ( p - n ).D v + D n0 ;

Simplified model of masking