SU1337875A1 - Method of determining parameter of frequency-contrast characteristic of photographic system - Google Patents

Abstract

This invention relates to the testing of photographic systems. The purpose of the invention is to improve the accuracy of determining the frequency-contrast photographic system. The device realizing the method comprises a scanning unit 1, a photoelectric converter 2, an amplifier 3, an analyzer 4 and a control unit 5. The introduction of new elements and the formation of new connections between the elements of the device does not lead to a shift in the estimates of the parameter of the frequency-contrast characteristic of the photo system and thereby allows the invention to be achieved. 3 il. (SL

Description

srig1

The invention relates to the testing of photographic systems (FS) and can be used to measure the frequency-contrast characteristics and resolution of photographic systems in a jump image on a photographic radiation receiver with a transparent substrate, for example, on photographic film.

The method is based on an assumption that 2P-20 is true for photographic systems with the angle of determining the parameter of the frequency-contrast characteristic of the ability to approximate characteristics.

Such systems are analytical expressions - 5 they light a beam of light of the image

A (x) j-exp f-4,6 (J-)

 (THAT

T (N) 1 5 exp -4.6 (1-)

 - "

j 2fr NX dx

(one)

de

A (x) T (N)

N

X

blur function; frequency-contrast characteristic, spatial frequency, spatial coordinate.

2л5

ETC

- the normalizing factor providing T (0). 1, T () 0.

With such an approximation, the characteristics depend on two parameters n and f. The search for parameters is facilitated by the fact that the value of n with sufficiently high accuracy can be determined on the basis of information on the composition of the FS (n 1.5, if the photo system contains one lens and film, n 1.75 if there is a shift). The task of determining the characteristics of the photo system is reduced to measuring only one parameter f, which is later for definiteness called the parameter of the frequency-contrast characteristic of the photo system.

The purpose of the invention is to improve the accuracy of determining the frequency-contrast photographic system.

FIG. 1 shows a diagram of a device implementing the method, FIG. 2, the dependence of the amplitude ratio of the harmonic components

Ci / C signal corresponding to the distribution of exposures in the image

jump in brightness, on parameter, on

R

FIG. 3 - dependence D - relative 78752

the difference of the amplitudes of the harmonic components of the signals corresponding to the distribution of exposures in the image (a jump in the brightness, and densities in the image of the jump in the brightness from the input signal parameter oL and the parameter f in Fig. 4 are graphs that explain the cyclical scanning of the image luminance.

The method is carried out as follows.

When determining the parameter of the frequency-contrast characteristic of scans

on a photo layer with a transparent substrate in the direction along the maximum density gradient of the image of the jump using the scanning unit 1. To do this, in the photo image obtained by this photosystem, find the image of the brightness jump and fix it in block 1 so that the scanning direction coincides with the direction of the maximum density gradient of the image of the jump. Using a photoelectric converter 2 and a logarithmic amplifier 3, the energy of the beam passing through the photo layer is converted into an electrical signal. This signal corresponds to the density distribution in the jump image.

The output signal of block 3 is laid out on the harmonic components using the harmonic analyzer 4. Image scanning is performed by reciprocating the beam by changing the starting point at a constant scanning interval. This scanning mode is implemented by the control unit 3. Scanning interval 6 is entered into block 5 before scanning begins. The position of the scan start point 7 can be changed during the scanning process. By changing the position of the starting point at a constant scanning interval, a point is determined that corresponds to an electrical signal from the output of block 3 with a minimum amplitude of the 2nd harmonic component. Then, the amplitude values of the 1st and 3rd harmonic components of this signal are measured using harmonic analyzer 4 and their ratio is calculated. According to the value of the amplitude C t and the ratio of the amplitudes Cj / C, su

3P

d t about the characteristics of the photographic system.

The scheme of the device is based on serial equipment. The scanning unit 1, the photoelectric converter 2, the logarithmic amplifier 3, the control unit 5 are part of the automatic microdensitometer AMD-1. A selective microvoltmeter B 6-9 is used as a harmonic analyzer.

Cyclic scanning of the image of a brightness jump formed by a linear imaging system with a blur function (1) is as follows.

Let the system receive a signal in the form of a jump in brightness (S) with levels B and B. At the same time, the distribution of exposures in the image of S is measured using a scanning aperture of small dimensions compared to the width of the transition zone of exposures, performing a reciprocating motion in the direction maximum exposure gradient in the jump image (Fig. 4a). The swing of x is greater than the width of the transition. In this case, a periodic signal H (t) is observed at the output of the photoelectric converter, at which the luminous flux passing through the measuring aperture is incident (Fig. 45). If the aperture performs symmetrical oscillations about the middle of the transition, then H (t) is formed by the mirror image of the transition curve f (x), symmetric about the middle of the period of oscillation of the aperture. In this case, the resulting picture coincides with the picture that occurs when a linear scanning of a stroke raster with a spatial period of 2x and a stroke width X (Fig. 4c) takes place. Let the distribution of the current exposure in the raster image

H (c) H, + (H, - H,) f (t) H, (1 + f (t).

de And ,, 1 f (r :)

exposure, corresponding to the regions with velocities B f and Bi, a periodic function obtained by the symmetric continuation of the transition curve f (x), which by definition is associated with

15

7875

the blur function is as follows f (x)

A (x) dx, 5 ° C - input signal parameter, H i - H - la,

Since H (t) is an even periodic 1Q periodic function, its spectrum has the form

C. (1 + oLf (t) cos-- dc,

Xx

to about, 1,. .., P. For nonzero K

2Н oL Ccf st

C. (t) cosdt (2)

 X j x

Since the blur function (1) is - 2Q symmetrical with respect to x O, the transition function f (x) is skew-symmetric with respect to the center of the transition. The f (c) signal has zero CK coefficients, with an even harmonic component of 25 in the case of symmetry of the aperture oscillations about the center of the transition. Thus, the condition С О, К 2п, ПО, 1, 2 ... can be taken as a criterion for adjusting the oscillations of the aperture on the image of a brightness jump.

From (2), it can be seen that the exposure spectrum H (t) is linearly related to the parameter o (. And H. The normal spectrum to C, receive ratios that do not depend on oi. And H,

35

WITH

f (t)

ABOUT

0

 {f (t) cos

(3)

Ck

Link - with the parameter f is easy

WITH

set by approximation of the calculated dependencies - from P. Therefore, 5, .Li J

l r

mu P f (p) can be used as

-one

estimate parameter p. Since the signal-to-noise ratio deteriorates as the K number increases, the optimum estimate o is f (-), and the criterion J1,

settings Cj 0. Dependence at Cj. O from p to p 2 in the expression

5 is shown in FIG. 1. Grade f

/ -

 f (-) is not | p1p oh and consistent in the case of white noise.

Thus, as an estimate of the parameter f, the smear function A (x)

linear imaging system can

l r

accept p- f () with cyclic b (

scanning the image of a brightness jump while tuning to the transition by the Cj 0 criterion.

The task of determining the parameter f by the photic form

tographic system in the image of L G, - ° 1 G

a, - aj / C, J

sufficient accuracy (the error of approximation is 0.5% when changing p by A times and oi from O to 30) is approximated by a separable brightness quadraction; this is complicated by the fact that the model of the photographic system is nonlinear, because Optical density is described by a nonlinear dependence — the characteristic of the START curve.

The characteristic curves of the halo-silver layers have the property of 20 straightness of the middle region, which is described by the following relation

D / -lg (H / Hj, (4) where Ht is the inertia point,

g- - contrast ratio,

equal to the slope of the straight line.

Since the rectilinear portion is working in most cases, 30 the characteristic curve description is taken in the form (4). Therefore, the density distribution in the raster image is

D (t) Ig H, (1 + .f (t))}

 rlg ((t) + / 48 (H, / HJ,

where is a; - approximation coefficients Thus, as an estimate of the parameter j of the blur function of the photographic system, one can take

 , WITH, )

35

during cyclic image scanning when setting up to go to

GI 0 criterion.

The proposed method does not lead 25 to a shift in the estimates of the parameter of the frequency-contrast characteristic of the photosystem and makes it possible to improve the accuracy of determining the characteristics of the photographic system.

Formula I-3 gain

A method for determining the parameter of frequency-contrast characteristic of a photographic system based on a photograph based on scanning a ray of brightness in an image captured on a photo layer with a transparent substrate in the direction of the maximum image density gradient, converting the energy of the beam into an electrical signal and calculating The logarithm of this signal is different in that, in order to improve the accuracy of determining the frequency-contrast characteristic, scanning is performed in a reciprocating manner. PICs constant amplitude, varying start point scanning laid on the received signal r monic components, determining the point at which the amplitude of the second g

 About relationship C, / C,

for the spectrum of the signal, D (C) is defined by

s / rt

D b

WITH

Jig l + oCf (t)} cos- -dt

TTt

Jig (t) dt

Since the function of Ig f-} is nonlinear, the density spectrum during cyclic scanning of the image of a jump relative to the middle of the exposure transition has non-zero even harmonics, and their amplitude depends on the value of p and oi. . When adjusting the sweep by the criterion GI 0 value

-Jb differs from - by value

CA,%

errors 4 --- -. FIG. 3 L L,

given relative dependencies

D (/ 1 / Сз). 100% from i at od. Linali1 functions and

Uh

i -i) shows that she is with

with sufficient accuracy (the approximation error is 0.5% when p is changed by A times and oi is from O to 30) is approximated by a separable quadrade a; - approximation coefficients. Thus, as an estimate of the parameter j of the blur function of the photographic system, it is possible to take

 , WITH, )

when cyclically scanning the image when setting to go to

GI 0 criterion.

The proposed method does not lead to a shift in the estimates of the parameter of the frequency-contrast characteristic of the photo system and improves the accuracy of determining the characteristic of the photographic system.

formula and-3 gain

A method for determining a parameter of the frequency-contrast characteristic of a photographic system from a photograph based on scanning a brightness jump in an image taken on a photo layer with a transparent substrate in the direction of the maximum density gradient of the image, converting the beam energy transmitted through the photo layer into an electrical signal and calculating the logarithm of this signal, characterized in that, in order to increase the accuracy of determining the frequency-contrast characteristic, scanning is performed reciprocating tion with constant amplitude, varying start point scanning laid received signal into its harmonic components, determining the point at which the amplitude of the second harmonic

The voltages of the first and third harmonics and the amplitude value of the first harmonic are judged on the value of the parameter of the frequency-contrast characteristic.

1.0

0.8

l o /

a, s

four

P b

Sv

but

)

f

Editor N.Klsarla

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VPIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

. ----- - - - - - - - - - -Production and printing company, Uzhgorod, Projecto st., 4

Sriga

Compiled by Y. Ivanov

Tehred V.Kadar Proofreader A.Obruchar

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Claims (1)

A method for determining the frequency-contrast characteristic parameter of a photographic system from a photograph based on scanning a ray of light with a jump in brightness on an image obtained on a photograph layer with a transparent substrate in the direction of the maximum gradient of the image density, converting the beam energy transmitted through the photograph into an electrical signal, and calculating the logarithm of this signal, characterized in that, in order to improve the accuracy of determining the frequency-contrast characteristics, the scanning is done reciprocating nym constant amplitude, varying the initial scanning point laid received signal into its harmonic components, determine the point at which the amplitude of the second harmonic is minimal, and p'o relative amplitudes of the first and third harmonics and the amplitude value of the first harmonics of the judged value of the parameter chastotnokontrastnoy characteristics.