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

magenta

Triazetat base material

red 1

red 2

intermediat layer

green 2

cyan

yellow filter

green 1

blue 1

blue 2

cover layer

yellow

Colour picture development

Latent picture Colour development Bleaching Fixation

Spectral characteristics of pigments

• Lambert-Beer law:

– : absorption coefficient– l : layer thickness– d : concentration 1() = e- ()× l transmission at unit thickness

( ) exp(- ( ) )l d

Spectral transmission of pigments

Optical density

• D = - log (D

• Spectral density:

D() = -log(() ) = = -log[exp(-().d.l)] = ().d.l

• D1() = ().d(1).l, density at unit conc.

• D() = d . D1()

Total transmittance

• Transmittance:YMC

• Density:

D DY DM DC = dYDY dMDM dCDC

Units: dY = dM = dC = 1 gray equiv. conc.

Colour densities of a positive film

Colours produced

T t

with T X t z

i i

380

1 3

nm

780 nm

d

, ...

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 ():• Dn = C + log (H/H0)

• Dn = Dn0 - Dv

Dv: Density of objecta megvilágítás logaritmusa lg H

feketea n

egati

v film

denz

itása

Dn

fehér

D - D diagram of negativ film

H-D diagram of revers.film

D-D diagram of revers.film

• Du = Du0 + . Dv, where

– Du density of revers.film

– Dv 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.: Dp = p × Dv; Neg.: Dn = Dn0 - n × Dv;

– Combining the two: Dk = Dn + Dp = (p - n ).Dv + Dn0;

Simplified model of masking

0,5

0,0

A színes maszkolás elve

500 600 700

hullámhossz, nm

400

Maszkolt réteg

0,0

1,0

0,5

0,5

0,0

1,0

1,0

Sárga maszk

mellékdenzitással

Magenta réteg