Photographic color densitometer

Claim 2

A photometric device for determining the difference in optical density between a standard optical absorber and an unknown optical absorber comprising: a light source for generating light of a particular intensity incident on an optical absorber; optical coupling means for directIng said generated light through said optical absorber; selectable primary color filter means disposed in the optical path of light transmitted through said optical absorber; detector means for collecting light transmitted through said optical absorber and said selectable primary color filter means, said detector means providing a detector current proportional to the intensity of the selected spectral component of said transmitted light; voltage generating means coupled to said detector means for producing a voltage proportional to said detector current; a first operational amplifier means and associated variable feedback resistive means coupled to said voltage generating means, producing a voltage proportional to said detector current and wherein the gain of said first operational amplifier is adjustable by said variable feedback resistive means; a second operational amplifier means and associated feedback potentiometer means coupled to said first operational amplifier means for providing an adjustable resistive ratio and corresponding amplifier gain in inverse proportion to the intensity of each of the said individual spectral components of said transmitted light incident on said detector means corresponding to selectable color reference voltages generated by said second operational amplifier means for each of said individual spectral components of said incident light on said detector means; density calibration means coupled to said potentiometer means for displaying said difference in optical density; memory standard means coupled to said second operational amplifier means comprising a third operational amplifier means with selectable variable feedback resistive means and associated gain establishing said selectable color reference voltages wherein each selectable voltage corresponds to the intensity of light transmitted through said standard optical absorber and one of said selected primary color filters; voltage comparing means coupled to said third operational amplifier means and to a fixed voltage means; null detecting means coupled to said voltage comparing means providing an indication when said fixed voltage is equal to the voltage generated by said third operational amplifier.

Claim 3

The device as claimed in claim 1 wherein said selectable primary color filters are mounted on a cylinder coupled to a ganged memory selector switch.

Claim 4

The device as claimed in claim 1 wherein said detector means is a photomultiplier tube.

Claim 5

The device as claimed in claim 1 wherein said voltage generating means provides a low input impedance for said detector means and further provides means by which the gain of said voltage generating means can be adjusted so that the voltage of said voltage generating means remains constant for a given light level regardless of the sensitivity of the selected said detector means and further comprises voltage divider means wherein offset voltages of said voltage generating means and dark current of said detector means can be balanced to zero.

Claim 6

The device as claimed in claim 1 wherein said optical coupling means comprises an optical probe means disposed in the path of light transmitted through said optical absorber and fiber optic means between said probe means and said selectable primary color filters.

Claim 7

The device according to claim 1 wherein said means for indicating when said compared voltages are equal comprises a null detector including two oppositely poled parallel light emitting diodes which emit no light when a null is acheived.

Claim 8

A photometric device for determining the proper densities of a color compensating filter pack required to obtain color balance for a color negative to be printed and the proper exposure time for printing said negative comprising: a. a light source and optical coupling means for generating light of a predetermined intensity along a predetermined optical path; b. means for supporting a color compensating filter pack in the optical path of said light source; c. means for supporting a color negative in said optical path; d. selectable filter means supported in said optical path for passing selected spectral components of light generated by said light source, at least one of said selectable filters being a neutral filter which passes all of said spectral components; e. detector means for generating a detector current proportional to the intensity of said selected spectral components of light generated by said source; f. voltage generating means coupled to said detector means for producing voltages proportional to said detector current; g. a first and second operational amplifier means and associated variable feedback resistive means coupled to said voltage generating means for producing color representative voltages proportional to said detector current for said selected spectral components to said detector current; h. memory standard means comprising a third operational amplifier means and associated variable feedback resistive means coupled to said second operational amplifier for establishing selectable color reference voltages corresponding to said color representative voltages generated by selected spectral components of light which have passed through a spectrally neutral area of a standard color negative and a standard filter pack disposed in said optical path, wherein for a specified color component, the gain of said second and third operational amplifier means are adjusted to unity by selection of fixed feedback resistive means and said color reference voltage corresponding to said specified color component established by adjusting the gain of said first operational amplifier means by said associated variable feedback resistive means and said remaining color reference voltages established by adjusting said second operational amplifier gain to unity by said variable resistive feedback means and adjusting the gain of said third operational amplifier by said selectable resistive means for each of the remaining said spectral components, said memory standard means further including means for establishing an exposure reference voltage wherein the gain of said first operational amplifier is adjusted to unity by selection of a fixed feedback resistive means and the gain of said second operational amplifier adjusted to a specific value by said associated feedback resistive means; i. voltage comparing means coupled to a fixed voltage and said memory standard means for determining when said color and exposure representative voltages are equal to said color reference voltages and exposure reference voltage respectively; j. means for indicating when the compared voltages are equal; k. means for adjusting said color representative voltages and said exposure representative voltage to values equal to said color reference voltages and said exposure reference voltage, respectively, said color representative voltage corresponding to said specified color component being adjusted by said variable feedback resistive means associated with said first operational amplifier means and wherein the remaining said color representative voltages being adjusted by said variable feedback resistive means associated with said second operational amplifier means and wherein a fixed feedback resistive means associated with said first operational amplifier corresponding to unity gain being selected and said exposure representative voltage being adjusted to equal said exposure reference voltage by said variable feedback resistive means associated with said second operational amplifier means, said color representative voltages and exposure representative voltage being adjusted for each selected spectral component with the standard filter pack removed from said optical path and the light from said source passing through a spectrally neutral area of the color negative to be printed, said exposure representative voltage being adjusted with said generated light Passing through a highlight of the color negative to be printed, said proper compensating filter pack, and said neutral selectable filter, said adjusting means including scales for indicating the densities of said proper compensating filter pack required to obtain color balance for the color negative to be printed and the proper exposure time for printing said negative.

Claim 9

A photometric device for determining the proper densities of a color compensating filter pack required to obtain color balance for a color negative to be printed and the proper exposure time for printing said negative comprising: a. a light source and optical coupling means for generating light of a predetermined intensity along a predetermined optical path; b. means for supporting a color compensating filter pack in the optical path of said light source; c. means for supporting a color negative in said optical path; d. selectable filter means supported in said optical path for passing selected spectral components of light generated by said light source, at least one of said selectable filters being a neutral filter which passes all of said spectral components; e. detector means for generating a detector current proportional to the intensity of said selected spectral components of light generated by said source; f. voltage generating means coupled to said detector means for producing voltages proportional to said detector current; g. a first and second operational amplifier means and associated variable feedback resistive means coupled to said voltage generating means for producing color representative voltages proportional to said detector current for said selected spectral components to said detector current; h. memory standard means comprising a third operational amplifier means and associated variable feedback resistive means coupled to said second operational amplifier for establishing selectable color reference voltages corresponding to said color representative voltages generated by selected spectral components of light which have passed through a spectrally neutral area of a standard color negative and a standard filter pack disposed in said optical path, wherein for a specified color component, the gain of said second and third operational amplifier means are adjusted to unity by selection of fixed feedback resistive means and said color reference voltage corresponding to said specified color component established by adjusting the gain of said first operational amplifier means by said associated variable feedback resistive means and said remaining color reference voltages established by adjusting said second operational amplifier gain to unity by said variable resistive feedback means and adjusting the gain of said third operational amplifier by said selectable resistive means for each of the remaining said spectral components, said memory standard means further including means for establishing an exposure reference voltage wherein the gain of said first operational amplifier is adjusted to unity by selection of a fixed feedback resistive means and the gain of said second operational amplifier adjusted to a specific value by said associated feedback resistive means; i. voltage comparing means coupled to a fixed voltage and said memory standard means for determining when said color and exposure representative voltages are equal to said color reference voltages and exposure reference voltage respectively; j. means for indicating when the compared voltages are equal; k. means for adjusting said color representative voltages and said exposure representative voltage to values equal to said color reference voltages and said exposure reference voltage, respectively, said color representative voltage corresponding to said specified color component being adjusted by said variable feedback resistive means associated with said first operational amplifier means and wherein the remaining said color representative voltages being adjusted by said variable feedback resistive means associated with said second operational amplifier means and wherein a fixed feedback resistive means associated with said first operational amplifier corresponding to unity gain being selected and said exposure representative voltage being adjusted to equal said exposure reference voltage by said variable feedback resistive means associated with said second operational amplifier means, said color representative voltages and exposure representative voltage being adjusted for each selected spectral component with the standard filter pack removed from said optical path and the light from said source passing through a spectrally neutral area of the color negative to be printed, said exposure representative voltage being adjusted with said generated light Passing through a highlight of the color negative to be printed, said proper compensating filter pack, and said neutral selectable filter, said adjusting means including scales for indicating the densities of said proper compensating filter pack required to obtain color balance for the color negative to be printed and the proper exposure time for printing said negative.

Claim 10

The device according to claim 7 wherein said voltage generating means provides a low input impedance for said detector means and further provides means by which the gain of said voltage generating means can be adjusted so that the voltage of said voltage generating means remains constant for a given light level regardless of the sensitivity of the selected said detector means and further comprises voltage divider means wherein offset voltages of said voltage generating means and dark current of said detector means can be balanced to zero.

Claim 11

The device according to claim 7 wherein said selectable filters are mounted on a cylindrical filter wheel coupled to a ganged memory selector switch in said memory standard means.

Claim 12

The device according to claim 9 wherein said selectable filters comprise red, green, blue, and neutral filters.

Claim 13

The device according to claim 7 wherein said detector means is a photomultiplier tube.

Claim 14

The device according to claim 7 wherein said optical coupling means comprises an optical probe means disposed in the path of light transmitted through a color negative and compensating filter pack and fiber optics means between said probe means and said selectable primary color filters or said neutral filter.

Claim 15

The device according to claim 9 wherein said detector means is a photodetector disposed within said cylindrical filter wheel.

Claim 16

The device according to claim 7 wherein said voltage generating means comprises means coupled to said detector means for producing a voltage proportional to said detector current, a first operational amplifier means and associated variable feedback resistive means for amplifying said proportional voltage, and second operational amplifier means, said means for adjusting said color and exposure representative voltages including potentiometer means in the feedback path of said second operational amplifier means coupled to said first operational amplifier means wherein said potentiometer means provides a resistive ratio in inverse proportion to the intensity of the individual spectral components of the light incident on said detector means corresponding to said color reference voltages and said exposure reference voltage generated by said second operational amplifier means.

Claim 17

The invention defined in claim 14, wherein said memory standard means is coupled to said second operational amplifier means and comprises a third operational amplifier with selectable variable feedback resistors establishing selectable reference voltages, said reference voltages corresponding, respectively, to the intensity of light transmitted through said standard optical absorber standard color negative and corresponding filter pack and a respective one of said selected primary color filters or neutral filter.

Claim 18

The device according to claim 14 wherein said potentiometer means includes two scales thereon, one of said scales being calibrated to indicate the densities of said proper compensating filter pack and the other of said scales being calibrated to indicate said proper exposure time.

Claim 19

The device according to claim 15 wherein said potentiometer means includes two scales thereon, one of said scales being calibrated to indicate the densities of said proper compensating filter pack and the other of said scales being calibrated to indicate said proper exposure time or multiple thereof as determined by a selectable means.

Claim 20

The device according to claim 7 wherein said means for indicating when said compared voltages are equal comprises a null detector including two oppositey poled parallel light emittinG diodes with legends thereon which emit no light when a null is acheived wherein said legends indicate whether said compensating filtration should be added or subtracted.

Claim 21

The device according to claim 14 wherein said variable resistive means of said first operational amplifier comprises calibration means for said memory standard means.

Claim 22

The device according to claim 7 wherein an adjustable aperture means is provided in said optical path for varying the intensity of light transmitted to said detector means, said adjustable aperture means comprising a calibration means for said memory standard means.

Claim 23

The device of claim 7 wherein said memory standard means comprises interchangeable plug-in modules.