JPS6230480A - Automatic contrast converting system - Google Patents

Abstract

PURPOSE:To convert the density level of a picture conforming to sensation of brightness of a living body without manual operation by converting intensity gradation X to density gradation Y automatically by using a sensation output Y=(YM-Ym).X<n>/(X<n>+S<n>)+Ym. CONSTITUTION:It is supposed that the value of density level of a picture element 2 on the light receiving face 1 of a television camera such as CCD is X. A density gradation converting section 3 makes conversion processes of conversion function Y=(YM-Ym).X<n>(X<n>+S<n>)+Ym for the input signal X from the light receiving face 1, and supplies an output signal that indicates the density Y after conversion to a display system 4 such as a television picture etc. The density YM and Ym of the maximum limit value and the minimum limit value of the picture display system 4 are determined by characteristics of the picture display system. The initial density X becomes the density Y after conversion. When the level is expressed by Y=f(X), the density level of a picture that has contrast conformable with characteristics of sensation of brightness of a living body is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention automatically converts the density gradation to a contrast that exactly matches human senses by performing processing to change the density level of an image. This invention relates to an automatic contrast conversion method for displaying images.

[Prior Art] Conventionally, methods shown in FIGS. 7, 8, and 9 have been proposed for contrast conversion. 7th
The figure shows a case where the input density and the output density are linear. It is known that in the visual system of living organisms, input luminance information X is converted in a form close to the functional form of YmA eXn/ (Xn+Sn) (see Figure 2), where sensory output Y is (n is a positive number), therefore, the seventh
In the case of the figure, the gradation of the image is not easy to see, and in Figure 8, when the input is displayed as a logarithm, it becomes a straight line (
(solid line), but the difference between the maximum and minimum becomes very large, causing a glare and discomfort. Also, when it is sharply compressed as shown by the dotted line, it feels unnatural and unpleasant, and when it becomes a power function as shown in Figure 9, this is called gamma correction, but like the first two, Since there is no saturation characteristic, inconveniences occur at strong levels. in this way,
The conventional methods shown in FIGS. 7, 8, and 9 have a drawback in that they do not change the density level of the image in accordance with the visual characteristics of the living body.

[Problems to be Solved by the Invention] The present invention has been made in order to eliminate the drawbacks of the conventional method as described above. Intended for automatic conversion.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a constant S determined from the geometric mean of the density gradation of a predetermined pixel for the density gradation X of the pixel on the screen; A constant multifunction function Y = (YM - Ym) *
The present invention is characterized in that the density gradation X is automatically converted to the density gradation Y by using n/(Xn+sn)+Ym.

[Function] According to the present invention, the contrast can be automatically adjusted to the density level of the image that exactly matches the characteristics of the human eye and brightness sense, and the image has a contrast that matches the visual sense. is automatically obtained.

[Example] The present invention will be described in detail below with reference to the drawings.

The principle of this invention will be explained using FIG. Here, C
The density level value at a certain pixel 2 on the light-receiving surface 1 of a television camera such as a CD is defined as another. For the input signal X from the light-receiving surface l, the density gradation converter 3 performs conversion processing using the conversion function shown below, and outputs an output signal indicating the converted density Y to a display system such as a television screen. Supply to 4. Here, the densities YM and Ym of the maximum limit value and minimum limit value of the image display system 4 are values determined by the characteristics of the image display system. It is assumed that the initial density X becomes the density Y after conversion. The function at this time is Y = f(X) = (YM-Ym) ・X n/(
Xn + S n) + Y m is shown in Figure 2, and how to find it is shown below.
The density of the i-th pixel among N pixels (N≦M) is assumed to be Xi (where i=1.2...N).

First, there are two methods for determining the value of the conversion constant S. When x=S in the function y=b(x),
It can be seen that Y takes a value between the maximum and minimum. Here's how.

(1) The maximum and minimum density of the pixels of NIN is Xr
Letting n and xM, it can be seen that s4Y "Yi".

(2) If the density information of all of the N pixels is Xi (where i = 1.2...N), density information is usually perceived intuitively on a logarithmic scale, so When the average value S of the pixel density on a logarithmic scale is determined, S is found as follows by solving S from the equation of log5=(810gX1)/N'(,w1).

As described above, in both (1) and (2), S results in finding the geometric mean of the density information of pixels in a predetermined portion or the whole. There are two ways to find it: one using a digital computer and the other using an electronic circuit. The former can be calculated according to the formula; in the latter, each point of one pixel is read out, converted into a time series signal, applied to a logarithmic converter, integrated over time using a separator, and divided by the integration time. It is found by applying it to an anti-logarithm converter.

Next, how to obtain n will be explained. There are two ways to do this, and they are shown below.
The cumulative distribution function N(X) of the appearance frequency of pixel density gradation X is approximated by the function h(X) = Xn/(Xn + Sn) (see Figures 3(A) and (B)), that is, N (X)=N-Xn/(Xn+Sn).

The first method is to set the number of pixels with a density of S/a and aS or less (all) among the pixels in the same screen as when S was calculated as N, N2, respectively (see Fig. 3 (A)), This is a method for finding N, , N2. NI and N2 are as follows.

Therefore, if we take the logarithm with the base a for the ratio of N1 and N2, we get Ioga (N2/Nl) = n, so the value of n can be determined. Therefore, to find n,
This results in finding the ratio Nl/N2 between the number of pixels having a density equal to or less than S/a and aS. There are two ways to calculate NI and N2: one is to use a digital computer, and the other is to use an analog circuit. The latter consists of two different density level signals S/
A signal detected by a level detection circuit that detects a and aS is shaped into a waveform, and each is integrated. After passing each signal through a logarithmic conversion circuit, the difference is taken and multiplied by a constant.

The second method is to set the cumulative distribution function to N (X) and Nb=
N-X, rl/ (X, + Sn)N (l b
) = N sX2 / (N2 + 5I)) From the above two equations, (N2 /
I), so the value of n can be determined. therefore,
Similar to the first method, there are two ways to find the value n: one is to use a digital computer, and the other is to use an analog circuit.

When expressed as Y=f(X) in this way, the density level of the image has a contrast that exactly matches the brightness perception characteristics of the living body.

According to the present invention, it is possible not only to adjust images having various contrasts to an average density level that is compatible with human senses, but also to automatically adjust the contrast to an appropriate level. That is, when the contrast of the image is low, that is, when the range of change in the input density gradation is narrow, in order to widen it, it is necessary to convert as a function of density gradation conversion as shown by the curve at the time of nil in Fig. 4. .

Furthermore, when the width of the gradation change does not need to be widened, it can be narrowed (a curve for n x 1 is shown). In this way, by performing the process of converting the gradation of the density level of an image according to the present invention, it is possible to automatically obtain an image display with a contrast that exactly matches the density gradation to human senses. can.

Next, an embodiment of the present invention is shown in FIGS. 5 and 756.
In each case, the density signal The output Y whose gradation has been automatically converted according to Y = f(X) is supplied to the TV signal processing circuit 7 in FIG.
In the figure, it is supplied to an electronic still camera 8.

[Effects of the Invention] As described above, according to the present invention, it has been possible to obtain images with appropriate contrast by using films with different gamma values for the degree of contrast, that is, the degree of soft and high contrast, when photographing using photographic film. However, there is no need to go through the trouble of changing films, and the contrast can be automatically adjusted to an image density level that exactly matches the characteristics of the human eye's sense of brightness. Images with matching contrast are automatically obtained.

According to the present invention, it is possible to automatically bring the density gradation conversion in the photoreceptor cells of the human eye, that is, the contrast sensitivity to the most appropriate level, thereby providing image information approximately close to the information capacity of the eye. The present invention can be applied to various image processing devices such as high-quality televisions, cameras, television cameras, electronic still cameras, etc., which have a contrast suitable for visual perception.

It can bring about groundbreaking changes in various fields.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the principle of the automatic contrast automatic conversion method of the present invention, FIG. 2 is a graph showing the relationship between the input signal and output signal shown in FIG. 1, and FIG. 3 (A) , (B) is a graph showing a method for determining n using an approximation formula of the cumulative density distribution function of the appearance frequency of pixel density Graph showing. 5 and 6 are block diagrams showing an embodiment of the present invention, FIG. 7 is a graph showing a conventional contrast automatic conversion method when the input and output are linear, and FIG. 8 is a graph showing the case where the output is linear. Figure 9 shows the case where the output is proportional to the power function of the input (corresponding to gamma correction). It is a graph. 1... Light receiving surface. 2...pixel. 3...Density gradation converter, 4...Display system, 5...COD camera. 6...Density gradation conversion circuit. 7...TV signal processing circuit, 8...Electronic still camera. Figure 1 1″~L:
Figure 2 (A) Figure 3 Output concentration Figure 4 Figure 7 Figure 8

Claims (1)

[Claims] For the density gradation X of a pixel on the screen, a constant S determined from the geometric mean of the density gradation of a predetermined pixel, a constant n determined from the density gradation in the vicinity of S, and a constant Function Y=(Y_M-Y_m)・X^n/(X^n+S^n) determined from the maximum concentration limit value Y_M and the minimum limit value Y_m
An automatic contrast conversion method characterized in that the density gradation X is automatically converted to the density gradation Y by using +Y_m.