JPH02257131A - Correcting method for photographic density - Google Patents

Abstract

PURPOSE:To always obtain a target density and to exactly correct color balance by correcting a density according to the type of photographic printing paper. CONSTITUTION:The photographic printing paper is trial-printed under plural known exposing quantities, and each printing density is detected from each obtained print. A gamma coefficient is obtained from the difference between the detected print densities and the plural exposing quantities and the exposing quantity to obtain the target density is determined based on the obtained gamma coefficient. In a color laboratory system, the color balance and color slope are corrected based on the gamma coefficient which is obtained for each color. Thus, a print with a constant density is obtained regardless of the variable density of negative film and the type of a printing paper.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of correcting photographic density, and more particularly to a method of correcting photographic density for obtaining prints of constant (target) density in a laboratory system.

[Prior Art] In a laboratory system, it is desirable to obtain prints with a constant density regardless of the density of the negative or the type of photographic paper.

Color lab systems also require color balance correction and color slope correction to obtain a constant color tone.

[Problems to be Solved by the Invention] However, conventionally, the gamma coefficient (γ) of the photographic paper used has been treated as a fixed value. For this reason, the target density may not be obtained depending on the type of photographic paper.

The present invention eliminates the above-mentioned drawbacks of the prior art, and its purpose is to propose a photographic density correction method that provides a constant (target) density regardless of the type of photographic paper.

[Means and operations for solving the problem] In order to achieve the above object, the photographic density correction method of the present invention corrects the exposure amount based on the gamma coefficient obtained by measuring the test print density of photographic paper. The outline is to do the following.

Preferably, the outline is to perform color balance correction based on gamma coefficients determined for each color.

Preferably, the outline is to perform color slope correction based on gamma coefficients determined for each color.

In addition, in order to achieve the above object, the photographic density correction method of the present invention performs test prints on photographic paper at a plurality of known exposure amounts, detects each print density of the obtained prints, and The gamma coefficient is determined from the print density and the difference between the plurality of exposure amounts, and the exposure amount for obtaining the target density is determined based on the determined gamma coefficient.

Preferably, one aspect of the method is to obtain a gamma coefficient from two print densities closer to the target density among the print densities and a difference in exposure amount corresponding thereto.

[Description of Embodiments] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

Although not shown, the photographic processing apparatus used in the correction method of this embodiment includes a light source section that generates exposure light, an exposure control section that controls the amount of exposure, and a printing section that prints the negative image onto photographic paper. , a processing section for developing, fixing, and washing the photographic paper after exposure, and a drying section for drying the photographic paper.

<Color Balance Correction> FIG. 1 is a flowchart of the color balance correction processing procedure of the embodiment. This process uses a standard negative (normal gray), as well as blue (B) and green (G).
) and red (R) according to the present invention, accurate color balance is obtained.

Although only the B density correction procedure will be described in detail here, the same applies to the remaining G and R densities.

In the figure, in step S1, a target density APDa (the subscript means blue) to be finally obtained is set to the exposure control section. In step s2, a normal gray standard negative is set in the printing section. In step S3, put heat is taken.

In step S4, test prints are performed on photographic paper using a plurality of known exposure amounts.

FIG. 2 is a graph showing the gamma characteristic curve of the photographic paper of the example. In the figure, the exposure control section performs test exposure on different parts of the photographic paper using, for example, three exposure amounts a, b, and c. a is the exposure amount for normal printing, and the exposure amount (currently a) used by this apparatus during actual printing is held in this normal printing line. b is the exposure amount for sample prints 1 to 1, and is used during test printing. The exposure amount is a predetermined amount ([o g
It has a value (b=a+ffogE) shifted to the + side by E). Also, C is the exposure amount of other sample prints,
Also used only for test printing. Exposure amount C
The value (c=
a℃○gE).

Returning to FIG. 1, in step S5, each print density of the obtained test print is measured and each measurement result is input to the exposure control section. In this embodiment, each print density is measured using, for example, an external appropriate densitometer, and each measurement result is input to the exposure control section from a keyboard (not shown) or the like. As shown in FIG. 2, in this example, the normal density for the normal exposure amount a is TPDI], the sample density for the sample exposure ib is TPODB, and the sample density for the sample exposure amount C is TPUDB.

In step S6, (T P D n = A P D
a) Determine whether or not. If from the beginning or after one or more corrections (T P D n = A P D B
, ), there is no need for further correction and the process ends.

However, in this example, initially (T, PD).

APDn ) is not satisfied, so the process proceeds to the correction routine from step S7 onwards. That is, in step S7, the target concentration A
The difference between P D B and the normal density T P Da is determined. In step S8, the gamma coefficient (γ8) of the photographic paper is determined from the normal density TPDB and the sample density (TPODB or TPUD).

Which sample concentration to use is determined, for example, according to the following processing procedure. That is, in FIG. 2, the sample concentration TP
ODB is higher than the target concentration A P than the sample concentration TPUDn.
Close to DB. Therefore, it can be said that γ8 obtained using the sample concentration TPODB is closer to the target concentration γ8' than γ8 obtained using the sample concentration TPUDB.

Therefore, in this example, the sample concentration TPODB is used.

In addition, if such judgment is followed, especially the foot part of the gamma characteristic curve ■
Also, a good approximation of γB' is always given at the shoulder part (2).

Assuming that γ8 of the photographic paper at normal density is expressed by equation (1) and that γ8 is constant at target density, the relationship expressed by equation (2) is obtained.

From the relationship of equations (1) and (2) above, the target concentration A P D
In order to obtain +3, the exposure amount should be adjusted by the amount of correction from point a (△j
It is estimated that it is sufficient to shift the amount by 2ogEn) to the + side. This corrected exposure amount (ΔρogE,) is determined by equation (3).

In step S9, the exposure amount a of the normal print is corrected using the corrected exposure amount (Δβ○gE,) obtained. In other words, the exposure amount of the new normal print is a (=a+△ffog
En), and based on this, the process from step S2 is newly repeated.

In this way, the normal density T P D 'a approaches the target density A P D a by one or more correction processes, and at the same time, the normal density γB also approaches the target density γ8'. Then, when it is determined in step S6 that the process has ended, TPDB=APDB, and printing at the target density becomes possible. Further, γB at that point is the target concentration γ6'.

Color Slope Correction Color slope correction is known as a correction necessary to maintain the slope characteristics of this type of printer within an acceptable range.

In this embodiment, the conventional color slope correction is improved by using accurate γ8' obtained by the color balance correction described above. Here, the slope correction of B density will also be explained in detail. The same applies to the remaining G and R concentrations.

The overcorrection amount of B density (△βo g OE B ) is (
4) Determined by formula.

Δlog OE e γ B Furthermore, the under correction amount (ΔnogUEa) can be found using equation (5).

△logVEB γ B Here, 0TFDB Niopatest print density NTPDB
: Normal test print density UTPDB : Under test print density 0APDB : Over target print density NAPDB : Normal target print density UAPDa:
Under Target Print Density Note that in the description of the above-described embodiments, the measurement of print density and the input of the measurement results were performed by humans, but the invention is not limited to this. For example, the above operations may be automated by providing a density detection means and a detection result input means within the photographic processing apparatus.

[Effects of the Invention] As described above, according to the present invention, since the density is corrected according to the type of photographic paper, the target density can always be obtained and accurate color balance correction can be performed.

Further, according to the present invention, since accurate γ of photographic paper can be obtained, color slope correction can be performed more accurately.

[Brief explanation of drawings]

FIG. 1 is a flowchart of the color balance correction processing procedure of the embodiment, and FIG. 2 is a graph diagram showing the gamma characteristic curve of the photographic paper of the embodiment.

Claims (5)

[Claims] (1) A photographic density correction method characterized by correcting the exposure amount based on a gamma coefficient determined by measuring the test print density of photographic paper. 2. The photographic density correction method according to claim 1, wherein color balance correction is performed based on gamma coefficients determined for each color. 3. The photographic density correction method according to claim 1, wherein color slope correction is performed based on gamma coefficients determined for each color. (4) Make test prints on photographic paper with multiple known exposure amounts, detect each print density of the resulting print, and calculate the gamma coefficient from the difference between each detected print density and the multiple exposure amounts. . A method for correcting photographic density, characterized in that an exposure amount for obtaining a target density is determined based on the determined gamma coefficient. (5) The photograph according to claim 4, further characterized in that a gamma coefficient is determined from two print densities closer to the target density among the respective print densities and a difference in exposure amount corresponding thereto. Density correction method.