JPH04104671A - Luminance level changing method - Google Patents

Abstract

PURPOSE:To correctly execute a level change by preparing a histogram based on the luminance level of each infrared detector for each frame and calculating true minimum and maximum luminance levels by accumulating generation frequencies in the histograms. CONSTITUTION:A histogram preparation part 11 prepares the histogram based on the luminance level obtained from the output of each infrared detector for each frame, and an accumulated picture element number calculation part 12 accumulates the number of generated picture elements in a direction from the minimum luminance to the maximum luminance of the histogram. Next, the number of generated picture elements is accumulated in a direction from the maximum luminance to the minimum luminance of the histogram, and a minimum/maximum luminance level decision part 13 defines the luminance level when being the number of accumulated picture elements more than a set value Nthr as the true minimum and maximum luminance levels respectively. By using these true minimum and maximum luminance levels, a level change part 14 changes the luminance level in the next frame to the level of a signal processing side. Thus, the minimum and maximum levels are stabilized and can be correctly changed.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial application field (Figure 6) Prior art (Figure 7) Problem to be solved by the invention (Figure 8) Means for solving the problem (Figure 8) Figure 1) Effect (Figure 1) Example (a) An embodiment of the present invention (Figures 2 to 4) - Structure of the present invention (Figure 2) - Histogram creation section (Figures 2 and 3) Figure) - Cumulative pixel number calculation unit (Figure 3) - Minimum/maximum brightness level determination unit (Figure 2) - Level conversion unit (Figures 2 and 4) - Operation (b) Other embodiments of the present invention Example (Fig. 5) Effect of the invention [Summary] Regarding a brightness level changing method for changing the brightness level output from each infrared sensing element of a multi-element infrared detector in an infrared imaging device to a value in the brightness range of the signal processing side. .

The minimum and maximum brightness levels are not affected by the operating environment, infrared fluctuations, etc. and are stable, allowing for accurate level changes.
Therefore, the purpose of the present invention is to provide a method for changing the brightness level of an infrared imaging device (which can improve the accuracy of signal processing and also prevent the display screen from flickering). Create a histogram, accumulate the occurrence frequency from the minimum brightness to the maximum brightness in the histogram, and set the first brightness level when the cumulative frequency exceeds the set value as the true minimum brightness level. The frequency of occurrence is accumulated in the direction of minimum brightness, and the second brightness level when the cumulative frequency exceeds the set value is set as the true maximum brightness level, and the true minimum brightness level and maximum brightness level are respectively set on the signal processing side. The brightness level of each infrared sensing element in the primary frame is changed at a rate of changing to the minimum value and maximum value of the brightness range in the first frame.

[Industrial Application Field] The present invention relates to a method for changing the brightness level of an infrared imaging device, and in particular, the present invention relates to a method for changing the brightness level of an infrared imaging device, and in particular, the brightness level output from each infrared sensing element of a multi-element infrared detector in an infrared imaging device is changed to a brightness range on the signal processing side. This invention relates to a method for changing the brightness level to a value of .

As shown in FIG. 6, the infrared imaging device optically condenses infrared rays emitted from a target object and the vicinity of the target object using an infrared optical system 1, and cools the condensed infrared rays by a cooler 2. The multi-element infrared detector 3 converts it into an electrical signal,
After the electric signal is amplified by the amplifier 4, it is AD converted into digital image data by the AD converter 5 and inputted to the signal processing section 6. The signal processing section 6 performs predetermined analysis processing to confirm the position of the target object. Alternatively, a visible image is displayed on a display device (not shown) such as a CRT, and the target object is visually recognized based on the displayed image.

The multi-element infrared detector 3 is, for example, 64x64 or L2
It is constructed by arranging 8×128 infrared detecting elements in a matrix, and each infrared detecting element outputs an electric signal having a value (brightness level) corresponding to the intensity of infrared rays. Therefore, the image data output from the AD converter 5 is a digital representation of the brightness level.

[Prior Art] In an infrared imaging device using such a multi-element infrared detector, the brightness level (image data) obtained from each infrared detection element has a wide dynamic range DRi, for example 212, as shown in FIG. Although it has a dynamic range, the dynamic range DRo on the side that captures and processes image data (image data processing device, image display device, etc.) is considerably narrower than that, and has a dynamic range of only 2 seconds, for example. Therefore, it is necessary to convert the brightness level obtained from the infrared sensing element to a range on the signal processing side.

For this reason, conventionally, image data obtained based on the output of a multi-element infrared detector is referred to for each screen (referred to as a frame), and the minimum brightness level L win and the maximum brightness level L tsax of the detected image data of one frame are referred to. These minimum and maximum brightness levels are regarded as the minimum and maximum brightness levels for the next frame, and the levels are changed. That is, in the next frame, the luminance level L of each infrared sensing element is processed by signal processing at the rate at which the minimum and maximum luminance levels Lwin and Lax are changed to the minimum and maximum values Min and Max of the luminance range on the signal processing side. The brightness range M is changed to the brightness range M on the side. still,
In FIG. 7, DRd is the total background information range detected by the multi-element infrared detector.

[Issue 81 to be solved by the invention: When the operating environment of a multi-element infrared detector deteriorates,
For example, if the cooling temperature fluctuates, it will be sensitively affected, and the S/N
An infrared sensing element with a degraded ratio appears, and the output level of the infrared sensing element becomes unstable. Furthermore, fluctuations in infrared rays in the natural background similarly make the output level of the infrared detection element unstable. Therefore, even when detecting and imaging the same background.

The minimum and maximum brightness levels L win and L 11ax vary depending on the operating environment, infrared fluctuations, and the like. FIG. 8 is a histogram for explaining such a situation, and the horizontal axis shows the output level (11 degree level) of the infrared detection element.
The vertical axis shows the frequency of occurrence of a predetermined output level for one frame, and even when detecting and imaging the same background, the minimum and maximum brightness levels La1n and Lr5ax may vary depending on the operating environment, infrared fluctuations, etc. It fluctuates as shown by the arrow, and the histograms do not match completely.

In this way, conventionally, the minimum and maximum brightness levels L win + L rmax fluctuate due to the operating environment, infrared fluctuations, etc., so level conversion cannot be performed correctly, and even if the background is the same, the data after level conversion is not constant. However, there was a problem in that the accuracy of signal processing deteriorated and the displayed image flickered.

In addition, conventionally, the minimum and maximum levels were determined for each frame,
Since the level conversion in the next frame is performed using the minimum and maximum levels, if the brightness of the imaging background suddenly changes, the brightness on the screen will also change significantly, making it difficult to see.

From the above, it is an object of the present invention to stabilize the minimum and maximum brightness levels without being affected by the operating environment, infrared fluctuations, etc.
To provide a method for changing the brightness level of an infrared imaging device, which allows the level to be changed correctly, thereby improving the precision of signal processing, and in which the display screen does not flicker.

Another object of the present invention is that even if the brightness of the imaging background suddenly changes,
It is an object of the present invention to provide a method for changing the brightness level of an infrared imaging device, which can moderate the change and gradually increase or decrease the brightness on the screen.

Still another object of the present invention is to provide a method for changing the brightness level of an infrared imaging device, which allows level conversion by simple calculations.

[Means to solve the problem] FIG. 1 is a diagram explaining the principle of the present invention.

11 is a histogram creation unit that creates a histogram based on the image data (brightness level) output from each infrared detection element for each frame; 12 is a histogram from the minimum brightness to the maximum brightness direction or from the maximum brightness to the minimum brightness direction; 13 is a minimum/maximum brightness level determination unit that determines the brightness level when the cumulative pixel count exceeds a set value as the true minimum brightness level and maximum brightness level. Parts and 14 are the rate at which the true minimum brightness level and maximum brightness level are changed to the minimum value and maximum value of the brightness range on the signal processing side, respectively, and are level conversion parts that change the brightness level of each infrared sensing element in the next frame. be.

[The action histogram creation unit 11 creates a histogram in which the horizontal axis represents the brightness level and the vertical axis represents the frequency of occurrence, based on the image data (brightness level) obtained from the output of each infrared sensing element for each frame. After that, the cumulative pixel number calculation unit 1
2, the number of generated pixels is accumulated in the direction from the minimum brightness L win in the histogram to the maximum brightness, and the minimum/maximum brightness level determination unit 13 determines the first brightness level when the cumulative number of pixels exceeds the set value N thr. True minimum brightness level L
Let it be cmin. Next, the cumulative pixel number calculating unit 12 accumulates the number of generated pixels in the direction from the maximum brightness L max in the histogram to the minimum brightness, and the minimum/maximum brightness level determining unit 13 determines that the cumulative pixel number has exceeded the set value N thr. The actual second brightness level is the true maximum brightness level L c+ma
Let it be x. In such a state, the level converter 14
True minimum brightness level L emin and maximum brightness level L
The luminance level L obtained from each infrared sensing element in the next frame is changed to the level M on the signal processing side at the rate at which cmax is changed to the minimum value Min and maximum value Max of the luminance range on the signal processing side, respectively.

Near minimum brightness level L win or maximum brightness level L+i
If a predetermined number of infrared sensing elements near ax with degraded S/N ratios are excluded, the minimum and maximum brightness levels are stabilized. Therefore, the minimum luminance level L cmin obtained by the present invention
, the maximum luminance level L cmax is not affected by the operating environment, infrared fluctuations, etc. and is stable, and level conversion can be performed correctly to improve the accuracy of signal processing, and the displayed image does not flicker.

Further, the minimum/maximum brightness level determination unit 13 sets the average value of the first brightness level and the average value of the second brightness level in the latest plurality of frames as the true minimum brightness level and the true maximum brightness level, respectively, and Using the minimum and maximum brightness levels, the level converter 14 changes the brightness level L obtained from each infrared detection element to the level M on the signal processing side. Thereby, even if the brightness of the imaging background changes suddenly, the change can be alleviated and the brightness can be gradually increased or decreased on the screen.

Furthermore, the level converter 14 converts the true minimum brightness level L c
min + true maximum brightness level Lcraax, the maximum value Max of the brightness range on the signal processing side, and the minimum value Min, the following formula (%) or linear formula M = (L - Lcmax) 37'r + Ma
xη= (Max−Min) / (LclI+ax
-LeIlin), the brightness level L of each infrared sensing element is converted to a value M on the signal processing side, and at this time (Lcm
The relationship between ax-Lcmin) and η is stored in memory, and (Lcmax-Lcmin) is calculated,
Since η corresponding to the calculation result is read from the memory and M is calculated, the level can be converted by a simple calculation.

[Embodiment (a) An embodiment of the present invention Book 111 Cut-out nose tree Fig. 2 is a block diagram of an embodiment of the present invention, and the same parts as in Fig. 1 are given the same reference numerals. In the figure, 11 is image data of each infrared detection element for each frame (11 degree level)
12 is a cumulative pixel number calculation unit that accumulates the frequency of occurrence (number of pixels) in the histogram from the minimum brightness L min to the maximum brightness direction or from the maximum brightness Lmax to the minimum brightness direction; 13 is the brightness level when the cumulative number of pixels Va exceeds the set value Nthr, is the true minimum brightness level L cmin,
A minimum/maximum brightness level determination section 14 stores the maximum brightness level L as wax, and 14 is a level conversion section that changes the brightness level L of each infrared detection element to the range of the signal processing section using the true minimum brightness level and maximum brightness level. It is.

15 is an address generation unit, and (1) when determining the true minimum brightness level Lc in, the address of the memory llb that stores the minimum brightness L win until the cumulative number of pixels Va becomes equal to or higher than the set value N thr (2) When determining the true maximum brightness level Lc+wax, the maximum brightness level is increased until the cumulative number of pixels Va exceeds the set value Nthr. Starting from the address that stores , the addresses are sequentially incremented in the downward direction and output. The 1m-bit image data (luminance level) L directly becomes the address of the memory llb that stores the frequency of occurrence of the luminance level L.

16 is a selector that selects the brightness level L expressed in m bits as an address when creating a histogram.
output, true minimum and maximum brightness levels L cmin, L
When determining tsax, the address output from the address generator 15 is selected and output.

Histogram Creation Unit The histogram creation unit 11 includes an address register 11a that stores the address output from the selector 16, and a memory (RAM) 1 l that stores the created histogram.
b, a read control unit 11c that reads data (occurrence frequency) from the storage location indicated by the address set in the address register, and a +1 adder lid that adds 1 to the occurrence frequency read from the memory when creating the histogram. It has a write control unit lie that writes the addition result to the memory.

The memory llb has at least 211 storage locations (addresses) corresponding to brightness levels, assuming that the dynamic range of one image data<m degrees is 21. Then, when creating a histogram, the brightness level L expressed in m bits is manually input.

The brightness level becomes the memory address as it is, and the frequency of occurrence (the frequency of occurrence of brightness level L, initial value is zero) is read from the address, and after +1 is added by the +1 adder 11d, it is stored at the original address. It has become. Thereafter, the above process is repeated every time the brightness level becomes an address and is set in the address register lla.
A histogram for one frame is created in memory llb.

Furthermore, when determining the true minimum brightness level L cmin and maximum brightness level L n+ax, the addresses (meaning brightness levels) output from the address generator IS are sequentially set in the address register lla, and the addresses are The frequency of occurrence (number of pixels of occurrence) is read out from the specified storage location.

Figure 3 is an example of the histogram HG created as described above, where the horizontal axis shows the output levels of 21'' infrared sensing elements (!
1 degree level), and the frequency of occurrence (number of pixels of occurrence) corresponding to each luminance level is plotted on the vertical axis. In addition, DRi is the dynamic range of the multi-element infrared detector, and DRd is the actual background information range for one frame actually detected by the multi-element infrared detector.

L win is the minimum brightness level, and L Llax is the maximum brightness level.

, image, ' The cumulative pixel number calculation unit 12 accumulates the number of generated pixels output from the readout control unit 11c when determining the true minimum and maximum brightness levels L c+1in−L Llax after creating the histogram. It is stored and output to the minimum and maximum brightness level determining section 13 at the subsequent stage.

When determining the true minimum brightness level Lc+sin, the address generator 15 starts from the address storing the minimum brightness Lwin, sequentially increases the addresses, and sets them in the address register lla. Therefore, the readout control unit 11c sequentially reads out the number of pixels at the minimum luminance level, the number of pixels at the next highest luminance level, etc. from the memory llb, and accumulates them by the cumulative pixel number calculation unit 12 (third (See the shaded area Act). Moreover, the true maximum brightness level Lcmax
When determining the maximum brightness Lma, the address generator 15 determines the maximum brightness Lma
Starting from the address where x is stored, the addresses are sequentially down and set in the address register lla. For this reason,
The readout control unit 11c determines the number of pixels where the maximum luminance level occurs;
The number of pixels where the next lowest luminance level occurs is sequentially read out from the memory llb and accumulated by the cumulative pixel number calculating section 12 (see the shaded area AC2 in FIG. 3).

Small/Large Level The minimum/maximum brightness level determining unit 13 includes a comparator 13a that compares the cumulative pixel number Va output from the cumulative pixel number calculation unit 12 with a preset setting value N thr;
When Va≧N thr, trigger pulse p t, p
t' and the true minimum and maximum brightness levels L cmin and L cmax
It has latch circuits 13c and 13d that store . Minimum brightness level L win and maximum brightness level L ax (
(Fig. 3) changes depending on the operating environment and infrared fluctuations in the natural background, and the range is relatively large. However, if a predetermined number of infrared sensing elements with degraded S/N ratios near the minimum brightness level and near the maximum brightness level are excluded, the minimum and maximum brightness levels become stable.

Therefore, in the present invention, the number of generated pixels is accumulated from the minimum brightness L + *in in the histogram in the direction of the maximum brightness, and the cumulative number Va of pixels is the predetermined number (set value) N.
The brightness level when the brightness level exceeds thr is set as the true minimum brightness level Lc++in, and the number of generated pixels is accumulated in the direction of minimum brightness from the maximum brightness Lmax in the histogram until the cumulative number of pixels Va is higher than the set value Nthr. The brightness level at which the brightness level becomes the true maximum brightness level Lcmax is set as the true maximum brightness level Lcmax. Note that the set value N thr is determined experimentally.

The comparator 13a causes the address generator 15 to increase the address (when determining the minimum brightness level) or decrease the address (when determining the maximum brightness level) until Va≧N thr.
When Va≧Nthr, the address generation section is made to stop generating addresses.

The trigger pulse generator 13b generates a minimum brightness level Lci
If Va≧N thr when determining n, the trigger pulse p
t, and the address (luminance level) generated from the address generator 15 at that time is set as the true minimum luminance level L c
When the maximum brightness level L cmax is determined and Va≧N thr, a trigger pulse Pt' is generated, and the address (brightness level) generated from the address generator 15 at that time is set to the true value. It is stored in the latch circuit 13d as the maximum luminance level Lcmax.

Level converter As shown in Figure 4, the true minimum brightness level in the previous frame is L c+++in + the true maximum brightness level is L
co+ax, and if the minimum value of the luminance range on the signal processing side is Min, the minimum value is Max, and the luminance level of the infrared detection element in the current frame is L, then the luminance level L is calculated based on the following formula % formula % (1) Or, the following formula M= (L-LcIIax) ” 'rl+Max
...(3) η= (May - Min) / (L
cmax −LcIIlin), it can be converted to a level M in the luminance range of the signal processing side.

Note that η is the conversion rate.

For this reason, the level converter 14 is configured in advance (L c+++ax
-Lcmin) and the conversion rate η.
4a, a subtracter 14b that calculates (L cmax −L c++in ) and generates the address of the memory 14a, and equation (1).

The minimum brightness level L cmin and the maximum brightness level L depend on which calculation formula in formula (3) is used for level conversion.
a selector 14c that selectively outputs cn+ax;
1) When converting the level using the calculation formula, (L −
L cmin), and in the case of level conversion using the calculation formula (3), a subtracter 14d that calculates (L - L cmax) and a memory 14 that stores the subtraction result of the subtractor 14d.
A multiplier 14e that multiplies the conversion rate η read from a, O when level conversion is performed using equation (1), and (3)
A correction level value generation unit 14f that outputs M a X as a correction level value when level conversion is performed using the formula
Add the correction level value to the 1 multiplication result and use formula (1) or (
3) It has an adder 14g that outputs the calculation result M of the equation.

1 run Next, the overall operation of FIG. 2 will be explained.

When image data indicating a brightness level L corresponding to the intensity of infrared rays detected by an infrared detection element is input, the histogram creation unit 11 uses the brightness level for one frame and plots the brightness level on the horizontal axis; A histogram with the frequency of occurrence on the vertical axis is created and stored in the memory llb.

When the histogram is created, the cumulative pixel number calculation unit 12 accumulates the number of generated pixels from the minimum brightness L@in in the histogram in the direction of maximum brightness, and the minimum/maximum brightness level determination unit 13 sets the cumulative pixel number Va. The first brightness level when the value N thr or higher is the true minimum brightness level L
It is stored in the latch circuit 13c as cmin.

Next, the cumulative pixel number calculating unit 12 accumulates the number of generated pixels in the direction from the maximum brightness L wax in the histogram to the minimum brightness, and the minimum/maximum brightness level determining unit 13 determines that the cumulative pixel number Va has exceeded the set value Nthr. The actual second brightness level is stored in the latch circuit 13d as the true maximum brightness level Lc+aax.

In such a state, when the next frame of image data is input from each infrared sensing element, the above-mentioned histogram creation process is performed, and the level converter 14 calculates the input luminance level L by formula (1) or The level conversion process of equation (3) is performed, and the obtained level M is input to the signal processing section.

It should be noted that a signal LC8 (level control switching signal) indicating whether to use equation (1) or equation (3) for level conversion is sent to the selector 14c and the correction level value generating section 1 in advance.
It is input to 4f. Moreover, in the memory 14a in advance, (
The relationship between L cmax - L cmin) and conversion rate η is stored, so that it is not necessary to perform the calculation of equation (2) including division. Therefore, equation (1) or (3
) can be easily calculated using only addition, subtraction, and multiplication.

Above, minimum brightness level L cmin, maximum brightness level L
cmax is not affected by the operating environment, infrared fluctuations, etc., so level conversion can be performed correctly, the accuracy of signal processing can be improved, and the displayed image does not flicker.

(b) Other embodiments of the present invention By the way, the minimum and maximum levels are determined for each frame,
If the level conversion in the next frame is performed using the minimum and maximum levels, if the brightness of the imaging background changes suddenly, the brightness will change frequently on the screen, making it difficult to see. for example,
When the brightness of a certain frame suddenly decreases, the screen will temporarily go dark, but in the next frame it will return to the original brightness before the sudden change, making it difficult to see as the brightness changes frequently. Therefore, in the present invention, the average value of the minimum and maximum brightness levels of multiple frames is taken to determine the true minimum and maximum brightness levels Lcmin,
It is set to L c++ax. As a result, in the example described above, once it becomes dark, the brightness does not immediately return to the original brightness, but gradually increases to make it easier to see.

Figure 5 shows the minimum and maximum brightness levels L cm of multiple frames.
2 is a configuration diagram of a minimum/maximum brightness level determination unit 13 that takes the average value of in, Lcmax as the true minimum and maximum brightness levels Lcmin', Lcmax', and the same parts as in FIG. 2 are given the same reference numerals. are doing.

In FIG. 4, the differences from the minimum/maximum brightness level determination section in FIG. 2 are (1) minimum and maximum brightness levels L cmin for the latest N frames (for example, 32 frames);
, L c+*ax is stored in the shift register 13e.
, 13f, and (2) the minimum and maximum brightness levels L cn+in , L crs for N frames.
ax is integrated, and the average value L cmin', L
The point is that average value calculation units 13g and 13h are provided for calculating cmax'.

Minimum and maximum brightness level L cmin of new frame
.

L c+sax is determined and the latch circuits 13c and 13d
When stored, the minimum and maximum brightness levels are shifted to the beginning positions of the shift registers 13e and 13f, and
the N smallest previously stored in the shift register,
The maximum brightness level is shifted to the right, and the last digit, in other words, the oldest minimum and maximum brightness levels are pushed out by one and disappear.

In addition, when calculating the average value, each shift register 13e
, 13f are sequentially shifted to the right by 1, while the average value calculation units 13g, 13
h and is integrated, as well as being input to the shift register 13.
e and 13f, and when it returns to its original position, the integration of the minimum and maximum brightness levels is completed. Thereafter, the average value calculation units 13g and 13h divide the integrated value by 1/N to obtain the average value L cmin', L of the minimum and maximum luminance levels (FIG. 2).
cmax' is calculated and the selector 14c (see Figure 2)
is output to the subtracter 14b.

With the method of using this average value as the true minimum and maximum brightness levels, even if the brightness of the frame changes suddenly, the true minimum and maximum brightness levels do not change suddenly, so the brightness of the screen changes slowly, making it easier to see. Become.

Although the present invention has been described above with reference to the embodiments, various modifications can be made to the present invention in accordance with the gist of the present invention as set forth in the claims, and the present invention does not exclude these modifications.

[Effects of the Invention] According to the present invention, a histogram is created for each frame based on the brightness level of each infrared sensing element, and the frequency of occurrence is accumulated from the minimum brightness to the maximum brightness in the histogram, and the cumulative frequency is calculated. The brightness level when the value exceeds the set value is the true minimum brightness level, and the occurrence frequency is accumulated from the maximum brightness to the minimum brightness in the histogram, and the brightness when the cumulative frequency exceeds the set value. Since the level is configured to convert the true maximum brightness level, depending on the operating environment, infrared fluctuations, etc., the minimum
The maximum brightness level is unaffected and stable, level conversion can be performed correctly and signal processing accuracy can be improved, and the displayed image does not flicker.

Further, according to the present invention, since the average value of the minimum brightness level and the average value of the maximum brightness level in the latest plurality of frames are configured to be the true minimum brightness level and the true maximum brightness level, respectively, the imaging background Even if the brightness of the
By alleviating the change, the brightness on the screen can be gradually increased or decreased to make it easier to see.

Furthermore, according to the invention, the true minimum brightness level Lcmin
, the true maximum brightness level Lcmax, (L c
+sax -L c+*in ) and the conversion rate η are stored in memory, and (L cmax -L c+*i
Since M is calculated by calculating η corresponding to the calculation result from the memory, the level can be converted by a simple calculation without division.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the principle of the present invention, Figure 2 is a configuration diagram of an embodiment of the present invention, Figure 3 is a diagram explaining histogram, Figure 4 is a diagram explaining calculation of level conversion, Figure 5 is minimum/maximum. Another configuration diagram of the brightness level determining section, FIG. 6 is a configuration diagram of an infrared imaging device, and FIG. 7 is an outline W8 explanatory diagram of level conversion. FIG. 8 is a histogram for explaining the conventional problems. 11. Histogram creation section 12. Cumulative pixel number calculation section 13. Minimum/maximum brightness level determination section 14. Level conversion section

Claims (5)

[Claims] (1) In a method for changing the brightness level of an infrared imaging device in which the brightness level output from each infrared sensing element of a multi-element infrared detector is changed to a value within the brightness range of the signal processing side, each infrared sensing element is changed every frame. A histogram is created based on the brightness levels of At the same time,
The occurrence frequency is accumulated from the maximum brightness to the minimum brightness in the histogram, and the second brightness level when the cumulative frequency exceeds the set value is the true maximum brightness level, and the true minimum brightness level and maximum brightness level are A brightness level changing method characterized by changing the brightness level of each infrared sensing element in the next frame at a rate of changing to a minimum value and a maximum value of a brightness range on a signal processing side, respectively. (2) The average value of the first brightness level and the average value of the second brightness level in the latest plurality of frames are set as a true minimum brightness level and a true maximum brightness level, respectively. How to change brightness level. (3) If the true minimum brightness level is Lcmin, the true maximum brightness level is Lcmax, and the maximum value of the brightness range on the signal processing side is Max and the minimum value is Min, then the following formula M = (L-Lcmin)・η η=(Max-Min)/(Lcmax-Lcmin)
3. The brightness level changing method according to claim 1, wherein the brightness level L of each infrared sensing element is converted to a value M on the signal processing side based on the following. (4) If the true minimum brightness level is Lcmin, the true maximum brightness level is Lcmax, and the maximum value of the brightness range on the signal processing side is Max and the minimum value is Min, then the following formula M = (L-Lcmax)・η+Max η=(Max-Min)/(Lcmax-Lcmin)
3. The brightness level changing method according to claim 1, wherein the brightness level L of each infrared sensing element is converted to a value M on the signal processing side based on the following. (5) Store the relationship between (Lcmax-Lcmin) and η in advance in memory, calculate (Lcmax-Lcmin), read η corresponding to the calculation result from the memory, and calculate the value M. The brightness level changing method according to claim 4 or claim 5.