SU805326A1 - Computing device for measurinc photographic system characteristics - Google Patents

Description

The invention relates to computing and can be applied to test photographic systems.

A device containing a microdepsitometer, a transducer, is known; Exposure Density, Keys / Rönoretor of clock pulses, pulse counter, pulse distributor -, control unit, memory blocks, subtraction unit, smart block, on-block, character definition}, dividing block and computing blocks 1,

This device is intended only for measuring the frequency-response characteristics (MTF) of photographic systems.

The closest in terms of technical essence to the invention is a device consisting of a microphotometer, an aperture distortion corrector, a coefficient converter, transmission to exposure, band-pass filters, quadrants, a subtraction unit, a frequency corrector, and a recording unit. The device works as follows: the rotating image of the radial world is scanned by the measuring micro-photo. meter An electrical signal proportional to the transmittance of the image of the worlds is fed from the output of the microphotometer to the aperture distortion corrector (the transmission coefficient of which changes depending on the spatial frequency of the world in the wearable: - microphotometer scanning system. From the output of the aperture distortion corrector, the signal is input to the converter pass into the exposure, from the output of which the signal goes to two band-pass filters. The first filter selects the sum of the main harmonic distributed and illumination in the image of the radial world and granularity at frequencies close to the fundamental harmonic, the second filter with a fundamental frequency of two

0 times smaller, only the noise caused by granularity i stands out. In this case, it is considered that the granular noise is white. Both signals are KBrated and then subtracted from each other.

5 with weights, inversely proportional to the filter passbands. The result of the subtraction is fed to the input of the frequency equalizer, where the lens effect of the resolver or collimator is eliminated, using

which was imprinted on the photographic image of the radial world, the output of the frequency equalizer receives a signal proportional to the square of the MTF value at a given spatial frequency. This signal, as well as the value of the spatial frequency corresponding to it, are recorded in a recording unit. This device largely automates the measurement process, automatically converts the transmittance to the exposure, calculates the values of the MPS and induces these values. The device used filtering of noise, granularity, which improves the accuracy of measuring the MTF 2.

However, the known device provides measurement only of the MEC and does not allow to measure such important characteristics of the photosystem as resolution and threshold characteristic.

The purpose of the invention is to enhance the functionality by providing a measurement of the threshold characteristic and resolution. The goal is achieved by including a device containing a microphotometer, aperture distortion corrector, transmittance-to-exposure converter, bandpass filters, quadrants, a subtraction unit, a frequency equalizer, and a recording unit , the first output of the microphotometer is connected to the first input of the aperture distortion corrector, the second output is connected to the first inputs of the block p Registration, frequency corrector and the second input of the aperture distortion corrector, the output of which is connected to the inputs of the first and second band filters through the transmittance-to-exposure converter; the outputs of which are connected to the input of the first quad and the second quad, respectively, the output of the first quad; subtracting, the output of the second quadrant is connected to the second input of the subtraction unit, the output of which is connected to the second input of the frequency quadrant; five blocks of cases are entered Two multipliers, a logarithm and an averaging block, an adder, two square root extraction blocks, a memory block, a comparison block and a switch, the output of which is connected to the second input of the registration block, the first inputs of the first and second division blocks are respectively connected to the output the first block of the square root and the output of the second quad, the input of the third division block is connected to the output of the aperture distortion corrector, the output of the third division block through serially connected logarithm block And the averaging unit is connected to the first input of the first multiplication unit, the second and third inputs of which are connected respectively with. the output of the third quadrant and the output of the second division unit, the second input of which is the first input of the device, the input of the third quadrant and the first inputs of the memory unit and switch are connected to the second output of the microphotometer, the output of the first multiplication unit through the series-connected fourth unit, the adder, the second the quadrate extraction block, the second multiplication unit and the fifth division unit are connected to the first input of the comparison unit and to the third input of the registration unit, the inputs of the fourth division unit, the sum, the second The multiplication unit and the fifth division unit are the second, third, fourth and fifth inputs of the device, the input of the first square root extraction unit is connected to the output of the frequency equalizer, the output is connected to the second input of the memory unit, the output of which is connected to the second input of the first the dividing unit, the output of which is connected to the second input of the comparison unit and to the fourth input of the registration unit, the output of the comparison unit is connected to the second input of the switch.

The drawing shows a diagram of the device.

The circuit contains microphotometer 1, aperture distortion corrector 2, transmittance-to-exposure converter 3, first band-pass filter 4, second band-pass filter 5, first quadrant 6, second quad 7, subtraction unit 8, frequency corrector 9, first square root extraction unit 10, memory block 11, first dividing unit 12, second dividing unit 13, third quadrant 14, third dividing unit 15, logarithm 16, averaging unit 1, first multiplying unit 18, fourth dividing unit 19, adder 20, second square extracting unit 21 cor n, the second multiplication unit 22, the dividing unit 23, the comparing unit 24, the commutator 25, the recording unit 26.

The resolution of the photo system (PC) can be defined as the spatial frequency corresponding to the intersection of the MTF and the threshold characteristic (PC), since PC is a solution of the equation T (N)) (1)

where T (N) is the CHK T (N) is nXj

N - spatial frequency, ivl.

Therefore, in order to find a PC (denoted by the symbol R), it is necessary in addition to the BNT of BtiaTb and HRP. It is known that HRP can be calculated by the formula

atiklfs .5

about (2)

Bt sial-noise ratio} gradient of the characteristic curve at the point c, the density of the human visual analyzer Tj, density dispersion of the human visualizer, the Selvin constant, which has the square root of the white noise spectrum of the granularity, i.e. Kg GO is the number of half periods of the worlds over which PC is measured. The main input parameters in the HR formula are: the ratio q, defined a priori, the gradient d, taken from the characteristic curve of the photographic material, the average optical density O in the image of the world, and Selvin Kg. The greatest difficulty in the computation of HRP is the assignment of a constant Kg. In a known device, the noise power is measured in a known narrow band fif. Consequently, at white frequencies of granularity. noise P (.Z.fjiL-, (3) s-.i where K is a coefficient that takes into account the steepness of the fronts of the frequency response of the filter allocating E. Consequently, to calculate LC, you must have a division unit, one of the inputs of which the signal proportional to E on the other is E. Having determined Kg, it is possible to calculate the photo materials HR. In addition, in order to calculate the PC, it is necessary to form a signal proportional to the average optical density. Also a signal proportional to the square of the spatial frequency is necessary ( Izve The device generates a signal H proportional to the square of the MTF of the photosystem, i.e. Hg This signal is fed to the registration unit which is graduated in the MTF values the registration option is irrational, because firstly the scale of the registration unit must be nonlinear and Precision accuracy will be low, and secondly, each time you start a measurement, it is necessary to set the initial MTF value, which increases the complexity of the measurement process. In order to eliminate these drawbacks, it is advisable to make some additional transformations: the signals H j allowing to obtain a signal proportional to the MTF of the photosystem Tpc (N). Since the ChKH

WITH)

-Sh H (h (0) is the signal amplitude at frequency. To find PC, equation (1) needs to be solved, for which the value of .ChKX is required at the current spatial frequency Nj ;, variable within the required limits, - T (M i) and at the same time — T (N) is applied to the separate inputs of the comparison block. At the moment when T (N) T (N) occurs, the solution of equation 1), and the corresponding frequency is resolution R The device. Works as follows. To measure all the characteristics of the photosystems — MF, HR, PC — the image of the radial world, obtained by testing the FS, is mounted on a scanning device and is rotated relative to the center of the radial world with a constant angular velocity. Microphotometer 1 generates a signal characterizing the time dependence of the transmittance of a portion of the film falling within the scanning target of the microphotometer, (t). This signal corresponds to a certain spatial frequency N, the value of which depends on the number of strokes of the world n and on the distance from the center of the world to the scanning shell. The electrical signal E (t), proportional to D.,), from the first output of microphotometer 1 is fed to the first input of the corrector 2 aperture distortion. From the second output of the microphotometer, there is a signal proportional to the spatial frequency N, which simultaneously arrives at. blocks, for the operation of which information is needed on the current value of the spatial frequency, i namely: corrector 2 aperture distortions, third quadrant 14, frequency corrector 9, memory block AND, switch 25 and recording unit 26. Corrector. 2 aperture distortion eliminates the signal distortion caused by the finite size of the scanning gap. The transmission coefficient of the corrector varies inversely with the change in the transfer characteristic of the scanning gap from the spatial frequency. A corrected signal is received from the output of corrector 2 aperture distortions, proportional to T, This signal is information: on the MTF of the test FS and MTF of auxiliary optical devices, such as a collimator, with the help of which FS is tested, on the noise of the photographic material granularity. This information must be divided for what in the device are the blocks from the 3rd to the 8th. Transducer 3 performs a non-linear conversion that translates the photo-image transmittance into exposures that were in effect in the emulsion film layer. Then the signal is proportional to the dependence H (t), where H is the actual exposure wave, is applied simultaneously to the separate inputs of the band-pass filters 4 and 5. The band-pass filter 4 is tuned to the main frequency of the signal. It provides the sum of two powerful signals. no noise image. worlds and granular noise powers at the same frequency; Band-pass filter 5 is tuned to a significantly different frequency, for example, differing not less than two times from the settings of filter 4. This filter provides the power output only of granular noise.

From the outputs of bandpass filters 4 and

5signals are sent to quadra.tori

6 and 7. and are raised or to the second power. Then signals are sent to separate inputs of subtraction unit B. Subtraction unit 8 deducts the incoming signals with weights inversely proportional to the passbands of the corresponding band-pass filters 4 and 5. From the output of subtraction unit 8, the second, the input of the frequency equalizer 9, receives a signal proportional to the square of the amplitude of the signal, caused by a seemingly noiseless image of the worlds. This signal is proportional to the product of the MTF of the FS and MTF of the auxiliary Optical system under study | for example, a collimator or resolver 1,

i.e. T T

h k

 Wed and.

where h is the amplitude of the signal arriving at the second input

frequency corrector; T) - MTF of the collimator;

K - coefficient.

The frequency equalizer 9 stores .in its Ps1m ty MTF of the collimator T i; and for each value of the frequency N, Jli-kT -n

Leading recount

nf-i fs e to

Thus, a signal proportional to the square of the MTF of the FS under study is removed from frequency equalizer 9. To get the value of the MTF at spatial frequency, this signal must be erected

J degree 0.5 and normalized in accordance with the formula (L) (normalized by definition, ensures that 0). These operations are performed by blocks 10–12. The first square root extraction unit 10 erects a signal arriving at its input, to a power of 0.5, the memory block stores the value of this signal at a spatial frequency N close to zero - H (; (( 0), and during the whole measurement cycle gives the memorized value to the second input of the first dividing unit 12, the first input of which receives the current signal H (N) npH of the npocTpaAj frequency, varying within the required limits. proportional to the measured normalized CHK -. T (N) This signal is simultaneously supplied to the input 26 of the recording unit and the input of the comparing unit 24.

From the output of the aperture distortion corrector 2, the curved signal proportional to IJCt) is successively applied to the third division block 15, the logarithm block 16, the averaging block 17, blocks 15 and 16 together convert the coefficient t into optical density D, which by definition

. D 1d l / t

When an image is scanned by a microphotometer, the signal t (t), and hence also D (t), is periodic. Block 1.7 averages the periodic signal D (t) and, from its output, outputs to the input of the first multiplication unit 18 a signal proportional to the average optical density F. Quadrator 14 raises the incoming signal, proportional to the current value of the spatial frequency, to the second power and outputs it to the input of the first block of 18 multiplication. The signal to the third input of block 18 is proportional to the square of SeLvin's nth to |, from the output of the second block 13 of the division. This signal is generated by block 13 as follows: at eio, the first input from the output of the second quad 7 receives a signal proportional to the power of granularity noise Nsc measured in the frequency band Afij. Dividing unit 13 divides this signal by the amount of this band, a signal proportional to which is fed to the second input of unit 13. This input is the input to the device. Therefore, in accordance with the physical essence of Selvin's constant, the output signal is proportional to it. square

AyL-K.i / 2

Iy 5 where K - coefficient.

The multiplication unit 18 multiplies the signals received at its inputs and returns the result to the input of the fourth division unit 19. Block 19 divides the signal received at its first input into a signal inputted at the second input and proportional to the number of dashed lines of worlds m, by which the PC is usually determined (for example, Ashcheulov’s five-third world). From the output of the fourth division block 19, the signal proportional to the second term in brackets in the formula (2) goes to the first adder 20. To the third input of the adder 20, a signal is proportional to the noise dispersion of the human visual analyzer Dg (first term in brackets in the formula ( 2)). From the output of the adder 20, the signal is sequentially fed to the input of the block

21 square-root extraction, multiplication unit 22 and division unit 23. These blocks complete the calculation of the peak contrast at frequency N; . ). According to the formula (noise q) and measured from the characteristic curve at the point where the optical density is equal to the average optical density ID, the gradient g signals are inputted at the inputs of the blocks

22 and 23. From the output of block 23 division. the signal is proportional to the threshold contrast at the frequency T. (N), the input of the registration unit 26 and the input of the comparison unit 24 are received. The unit compares the signals arriving at its inputs, If they are equal, which corresponds to the solution of equation (1), the comparison block sees the control signal to the input of the switch 25, which passes to the input of the registration unit 26 a signal carrying information about the PC of the FS under study.

The device is controlled by the operator. It introduces input data signals to the inputs of dividing units 13, 15, and 19, multiplication unit 22, and adder 20, and also changes the spatial frequency at which the MTF and HR values are measured. The frequency change is performed by changing the position of the scanning slit of the photo sensor of microphotometer 1 relative to the center of the radial world; As a result of one complete measurement cycle, in which the spatial frequency is varied within the required limits, in the registration block 26, the MTF FS, PC and PC will be recorded.

Claims (2)

1. Authors certificate of the USSR 442475, cl. G About F 15/20, 1972. 2. Journal of Scientific and Applied Photography and Cinematography, Volume 15, Issue 4. 1970, p. 256 (prototype)