GB2084348A

GB2084348A - Automatic determination of exposure

Info

Publication number: GB2084348A
Application number: GB8125431A
Authority: GB
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1980-09-22
Filing date: 1981-08-20
Publication date: 1982-04-07
Also published as: FR2490837A1; DK164246B; DE3136339C2; JPS5756836A; ES8303724A1; IT8124056A0; IT1139457B; KR850000501B1; GB2084348B; FR2490837B1; DE3136339A1; US4444506A; DK164246C; ES505474A0; IT8123000V0; DK376681A

Description

1 GB 2 084 348 A 1

SPECIFICATION

A Method and Apparatus for Correcting the 65 Reciprocity Law Failure of a Photosensitive Material This invention relates to a method and apparatus for correcting the reciprocity law failure 70 of a photosensitive material, for use in a picture reproducing machine such as a process camera, and the like.

As is well-known, a sensitivity of a color photosensitive material is depressed due to its reciprocity law failure when the illuminance is low. Hence, in order to perform a proper exposure, the exposure time should be corrected. Further, the reciprocity law failures of the three color layers of the photosensitive material are varied depending on the luminous energy, and accordingly the color balance is deteriorated.

Therefore, for example, the exposure time for a cyan filter is reduced and the exposure time for a yellow filter is increased.

Meanwhile, even when the exposure is properly performed depending on the average luminous energy by using an ideal photosensitive material whose reciprocity law holds good, or the above described correction of the reciprocity law 90 failure is carried out during the exposure which is performed depending on the average luminous energy by using a usual photosensitive material, a density failure and a color failure occur as follows.

That is, when the dark background of the picture is large, the essential part having a small light area is exposed excessively, and, on the other hand, when the light background is large, the essential part having a small dark area is exposed insufficiently. When the red, green or yellow background of the picture is large, the red, 100 green or yellow color is emphasized in a small essential part.

Heretofore, various methods for correcting such density and color failures have been developed. However, the corrections of the reciprocity law failures against the luminous energy and the color layers of the photosensitive material have been carried out depending on the experiences of a skilled person.

Summary of the Invention

We have identified a requirement for a method for correcting the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine, free from the aforementioned defects, which is simple, stable and reliable and which is capable of performing a quick operation without any skill.

We have also identified a requirement for an apparatus for correcting the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine, free from the aforementioned defects, which is simple, stable However, in practice, this equation (1) is not and reliable and which is capable of performing a satisfied by reason of the reciprocity law failure of quick operation without any skill. The invention is 120 the photosensitive material, and the following intended to meet at least some of these requirements.

According to the present invention there is provided a method for correcting the reciprocity law failure of a photosensitive material to be exposed, for use in a picture reproducing machine, comprising the steps of (a) detecting a luminous energy of an original picture, (b) comparing the luminous energy detected with a standard luminous energy predetermined, and (c) obtaining an exposure time by using the comparison result, a standard exposure time predetermined, and a correction factor predetermined for the reciprocity law failure of the photosensitive material.

According to the present invention there is also provided an apparatus for correcting the reciprocity law failure of a photosensitive material to be exposed, for use in a picture reproducing machine, comprising (a) a light detector which detects luminous energies of an original picture to be reproduced and a standard picture to obtain an exposure luminous energy and a standard luminous energy, (b) data setup means which records the standard luminous energy, a standard exposure time predetermined, and a correction factor predetermined for the reciprocity law failure of the photosensitive material, (c) an arithmetic unit which compares the exposure luminous energy with the standard luminous energy, and calculates the first exposure time by using the comparison result and the data recorded in the data setup means, and (d) a calculator which calculates the second exposure time for each color from the first exposure time.

Brief Description of Drawings

In order that the present invention may be better understood, preferred embodiments thereof will be described with reference to the accompanying drawings, in which:

Fig. 1 is a graph showing a reciprocity law failure of a color photosensitive material; Fig. 2 is a graph showing reciprocity law failures of color layers of a color photosensitive material; and Fig. 3 is a block diagram of an apparatus which performs a method according to the present invention.

Description of Preferred Embodiments

Generally, when the reciprocity law of a photosensitive material holds good, the following equation is satisfied, wherein E. means a standard luminous energy, TO means a standard exposure time, E means an exposure luminous energy for a correct exposure, and T means an exposure time.

T EO TO E (1) empirical equations wherein a means a correction factor, are obtained on the basis of experiences.

2 GB 2 084 348 A 2 When E<E.; When EiE,; T EO ---0 +a)-a (2) TO E T EO TO E0 +a)-Eoa (3) In Fig. 1, there is shown a characteristics curve (b) of the reciprocity law failure of a photosensitive material, which satisfies the equations (2) and (3). A line (a) represents 65 characteristics of a photosensitive material when a is zero, viz., the reciprocity law holds good. The curve (b) well represents characteristics of the reciprocity law failure of an available photosensitive material when a is 1.6.

Then, a correction amount or value F of the reciprocity law failure, when the photosensitive material is exposed under the luminous energy E by using a cyan, magenta or yellow filter, hereinafter referred to as a C, M or Y filter is calculated by the following empirical equations wherein P means a correction factor, which is obtained on the basis of the experiences.

When E<EO; When E E0; EO F=(- -1)P E E F=(- - 1)p "C (4) (5) In these equations, the correction factor P is 90 determined in the following.

For the C filter: When E<E.; When EE,; P=1 For the M filter: When E<E& When EE,; P= -1 For the Y filter: When E<E.; fl=4 When E:E,); 0= -4 In Fig. 2 there are shown correction value curves (d), (e) and (f) for correcting the reciprocity 100 law failures of the C, the M and the Y filters used during the exposure of the photosensitive material, which satisfy the equations (4) and (5).

A curve (c) represents characteristics of a photosensitive material when P equals zero, i.e.

the reciprocity law holds good. The curves (d), (e) and (f well represent characteristics of color layers of an available photosensitive material. The curves (d), (e) and (f) show that it is necessary to reduce the exposure time for the C filter and to increase the exposure.times for the M and the Y filters when the standard luminous energy EO is more than the exposure luminous energy E, and that it is necessary to increase the exposure time for the C filter and to reduce the exposure times for the M and the V filters when the standard luminous energy E. is at least the exposure luminous energy E.

In practice, in order to correct the reciprocity law failure, it is possible to increase the exposure times for the M and the Y filters instead of the reduction of the exposure time for the C filter when the standard luminous energy E. is more than the exposure luminous energy E, and to increase the exposure times for the C and the M filters instead of the reduction of the exposure time for the Y filter when the standard luminous energy EO is at least the exposure luminous energy. E, depending on the fact that the correction value for the Y filter is lesser than that for the M filter, as shown in Fig. 2.

In Fig. 3 there is shown a block diagram of an apparatus of the present invention which performs a method for correcting the reciprocity law failure of a photosensitive material according to the present invention.

A light detector 6 comprising a photo sensor is positioned in the front or the rear of a photographing lens of a copying apparatus, and detects average luminous energies E. and E of a standard picture and an original picture to be reproduced prior to the exposure operation.

A data setup means 7 inputs fundamental data such as the standard luminous energy E0, the standard exposure time T., the correction factor a of the reciprocity law failure for the luminous energy, the correction factors Pc, Pm and Py for correcting the reciprocity law failures for the C, the M and the Y filters, a density failure correction factor Q, if necessary, color failure correction factors RC, RM and RY, if necessary, by operating switches arranged on an operational board.

A discriminator means 8 receives the output signals from the light detector 6 and the data setup means 7, and discriminates which is larger, the standard luminous energy E. or the exposure luminous energy E, i.e. E<E, or E-:E,.

An arithmetic means 9 for correcting the reciprocity law failure comprises a pair of calculators 9a and 9b, and calculates the exposure time T for which the reciprocity law failure of the luminous energy is corrected, and the correction values Fc, Fm and Fy for which the reciprocity law failure of cyan, magenta and yellow colors are corrected, from the average luminous energy E and the fundamental data suc11 as the standard exposure time T., the standard luminous energy E,, the correction factors a, PC, pm and Py, and the like, as follows. That is, when the discriminator means 8 discriminates E<E, or EE,, the calculator 9a or 9b calculates the exposure time T and the correction values Fc, Fm and FY according to the equations (2) and (4), or (3) and (5).

Then, the density failure and the color failure are corrected by using the density failure correction factor Q and the color failure correction factors RC, RM and RY, as occasion demands.

An arithmetic means 10 for selecting filters and adjusting the correction values comprises a discriminator 1 Oa, a subtractor 1 Ob and an adder 4 3 GB 2 084 348 A 3 1 Oc. The discriminator 1 Oa discriminates the correction values Fc, Fm and F. calculated in the arithmetic means 9, and then, when these values are all positive, a certain number is subtracted from every correction value in the subtractor 10b so that one of the correction values may become zero, or when at least one of the correction values Fc, Fm and Fy is negative, a certain number is added to every correction value in the adder 1 Oc so that the minimum value may become zero.

For example, when the correction values FC, FM and Fy are -6%, 6% and 24%, respectively, 06 is added to every correction value to obtain Fc=O%, FrA=1 2% and Fy=30%.

An exposure time calculator 11 receives the output signa Is from the arithmetic means 10 and calculates the exposure times for each color as follows. Assuming that the large correction value such as F,=30%, and the smaller correction value such as FM= 12%, except zero such as Fc=O%, obtained in the arithmetic means 10, are F, and F2. a white light exposure time Tw when the photosensitive material is exposed by the white light, an independently used exposure time T1 when the photosensitive material is exposed by using the color filter for the larger correction value F1, and a jointly used exposure time T. when the photosensitive material is exposed by using the color filters for the correction values F1 and F2, are calculated by the following equations, wherein Cl and C2 mean exposure factors for the two filters.

T.(1 00-Fl) TW M(Fi-F2) T1 Cl. 100 TY2 T2 C11C2.1 00 Therefore, the total exposure time is the sum of Tw, T, and T2, and then, if necessary, the correction of the density failure and the color failure are carried out.

A display 12 receives the exposure times Tw, T, and-T2 calculated in the calculator 11 and displays them. The numbers of the exposure times Tw, T1 and T2 displayed on the display 12 are started to be subtracted when the exposure is started, and then they become zero when the exposure is finished.

Although the present invention has been described with reference to preferred embodiments thereof, however, various changes 110 and modifications can be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A method for correcting the reciprocity law failure of a photosensitive material to be exposed, for use in a Picture reproducing machine, comprising the steps of:

(a) detecting a luminous energy of an original picture; (b) comparing the luminous energy detected with a standard luminous energy predetermined; and (c) obtaining an exposure time by using the comparison result, a standard exposure time predetermined, and a correction factor predetermined for the reciprocity law failure of the photosensitive material.

2. A method as defined in claim 1, wherein the correction factor for the reciprocity law failure of the luminous energy is predetermined.

3. A method as defined in claim 2, wherein the correction factor for the reciprocity law failure of each color is predetermined.

4. An apparatus for correcting the reciprocity law failure of a photosensitive material to be exposed, for use in a picture reproducing machine, comprising:

(a) a light detector which detects luminous energies of an original picture to be reproduced and a standard picture to obtain an exposure luminous energy and a standard luminous energy; (b) data setup means which records the standard luminous energy, a standard exposure time predetermined, and a correction factor predetermined for the reciprocity law failure of the photosensitive material; (c) an arithmetic unit which compares the exposure luminous energy with the standard luminous energy, and calculates the first exposure time by using the comparison result and the data -90 recorded in the data setup means; and (d) a calculator which calculates the second exposure time for each color from the first exposure time.

5. An apparatus as defined in claim 4, wherein the data setup means records correction factors for the reciprocity law failures of the luminous energy and each color, and wherein the arithmetic unit further calculates a correction value for the reciprocity law failure of each color.

6. An apparatus as defined in claims 4 or 5, further comprising a discriminator which discriminates which is larger, the exposure luminous energy or the standard luminous energy, wherein the arithmetic unit performs the calculation depending on the discrimination result.

7. An apparatus as defined in claims 5 or 6, further comprising an arithmetic means which adds or subtracts a certain number to or from every correction value so that one of the correction values may be zero.

8. A method of determining the exposure requirement of a photosensitive material substantially as described herein and as illustrated in the accompanying drawings.

9. Apparatus for determining the exposure requirement of a photosensitive material 4 GB 2 084 348 A 4 substantially as described herein with reference to the accompanying drawings.

10. Photographic reproduction apparatus comprising apparatus as defined in any one of 5 claims 4 to 7 and 9 Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.

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