Panasonic first launched the first generation of wide dynamic CCD cameras in 1977; in 1999, it launched the second generation; from 2003 to 2008, it launched the third generation super dynamic CCD camera again. In the meantime, Sony, JVC, Samsung, etc. have also launched their own wide dynamic CCD camera. Up to now, in the technical reforms in the field of security monitoring, the rapid development of the security industry has been driven.
Since the natural light is arranged from 120,000 Lux to 0.00035 Lux in the night of the starlight, the indoor illumination is 100 Lux, and the illumination of the outside scenery may be 10000 Lux. Therefore, when the camera looks out of the window from the inside, the contrast between the two is 10000/100=100:1. This contrast can be easily seen by the human eye because the human eye can handle a contrast ratio of 1000:1, but the traditional security surveillance camera does not, because it only has a 3:1 contrast performance. Therefore, when a security surveillance camera is applied to a scene with a large contrast or backlight, the exposed areas of the entire image are overexposed and the dark areas are underexposed, and the brightest and darkest parts of the image are not visible.
Such as in bank depositories, entrances and exits of important places, etc. Because the glare from the window and the soft light from the fluorescent light on the ceiling may make it difficult to capture the indoor and outdoor scenes at the time, it is impossible to clearly capture the indoor and outdoor scenes with great contrast. The image taken may have a background that is too bright and the foreground is too dark, or the background is clear and the foreground is too dark and the foreground is suitable for the background to be too bright. The earliest solution, generally using backlight compensation technology or erecting two cameras indoors and outdoors to adapt to large light contrast, but the effect is not satisfactory. The technology to extend the dynamic range has emerged, which is the wide dynamic WDR (WideDynamicRange) technology.
Basic concept of camera dynamic range
The CCD wide dynamic technology uses a special DSP (digital signal processing) circuit to perform the most appropriate shutter speed exposure for the bright portion, and then exposes the dark portion to the most suitable shutter speed, and then performs two DSP processing on the image. Combine so that both the bright part and the dark part can be seen clearly. Although the 160-fold dynamic range technology has the advantages of large wide dynamics and optimization of image grayscale, it requires high DSP performance (especially processing speed). At present, due to the limitations of the CCD, even with multiple exposure sampling, the camera's wide dynamic range can only reach 66dB.
Obviously, due to the limitation of the photographic characteristics of the CCD, it is technically difficult to make a major breakthrough, and the CMOS camera has outstanding performance due to its excellent performance. For example, the linear range of the general linear output mode can reach 40~60dB; the D28 of the IM28-SA type CMOS camera with linear-logarithmic output mode in Canada can have a dynamic range of up to 120dB; Apical Co., Ltd. combines Altera's CycloneIII and CycloneIVFPGA, using the AptinaMT9M033720pWDRCMOS image sensor, also introduced a CMOS wide dynamic camera with both bright and dark parts visible; PIXIM USA developed CMOS-DPS technology, and its chipset has performance from D1000, D1500, D2000 to D2500. The speed is improved: the image sharpness is increased from 480 lines to more than 540 lines; the minimum illumination is from 1.0Lux/F1.2 to 0.5Lux/F1.2; the typical wide dynamic range is from 95dB to 120dB. According to the news, some CMOS wide dynamic technologies have even reached 160dB. Therefore, it is foreseeable that future surveillance cameras belong to wide dynamic cameras, while wide dynamic technology belongs to CMOS.
At present, in the global market, there are about 100 types of wide dynamic cameras in more than 50 countries put into practical use, but most of the camera manufacturers use Pixim's DPS technology. This is because the core technology of the DPS chip is to have an ADC in every pixel. That is, at an accurate capture point, the optical signal is converted into a digital signal. The benefit of this is that there is no crosstalk between pixels and no signal loss.
Basic concept of camera dynamic range
The so-called wide dynamic reality means that the camera can simultaneously see the illuminance ratio of the brightest and darkest parts of the image. The "dynamic range" refers broadly to the span that a change thing may change, that is, the region between the lowest pole and the highest pole of the change value. The description of this region is generally between the highest point and the lowest point. Difference. The “dynamic range†of the camera refers to the ability of the camera to adapt to the illumination of the scene in the scene, specifically the range of brightness (contrast) and color temperature (contrast). This means that the camera's most "dark" and "bright" adjustment range for the image is the ratio of the brightest to darkest tones in a still image or video frame. The hue can show the precise details in the image or frame. As the ratio of the two tones, the unit of dynamic range can be decibel, bit, file, or simply expressed as a ratio or multiple. The conversion method between various units is shown in Table 1.
The 20-speed dynamic range is listed because it covers almost all the dynamic range that the human eye can distinguish. The dynamic range beyond these gears has little practical significance. The reason why the human eye can distinguish such a wide dynamic range is because when people observe the real scene, the pupil, iris, retina and related muscles interact and dynamically adjust. At the same time, the brain integrates all the "exposure elements" into A coherent image that reflects the very bright or very dull tones of the real scene with extreme precision.
JVC dynamic range test method
Compared to the human eye, for standard CCD and CMOS image sensors, the exposure (collecting photons) time of all photosensitive cells is the same. The photosensitive unit collects more photons for the bright part of the scene, and fewer photons for the dark part. However, the number of photons that the photosensitive unit can collect is limited by the wellcapacity, so that the photosensitive unit that captures the brighter color of the object may overflow or saturate. To prevent this from happening, you can reduce the exposure time. However, if you do this, the photosensitive unit that captures the darker tones of the object may not be able to collect enough photons. Therefore, for a typical single exposure image sensor, the upper limit of the dynamic range is limited by the well capacity of the photosensitive unit, and the lower limit is limited by the signal to noise ratio of the photosensitive unit. Thus, the dynamic range of the CCD image pickup device under the peak noise refers to a saturated output voltage and dark field - the ratio of peak voltage, i.e. the dynamic range <br> <br> = Usat / UNp-p (1 )
In the formula (1), Usat is the output saturation voltage; UNP-P is the peak-to-peak value of the noise.
Obviously, the dynamic range can also be defined and calculated as the ratio of the maximum amount of charge that can be stored in the CCD well and the amount of charge determined by the noise; the value is also the signal peak voltage and the rms noise voltage at the output. Ratio (usually expressed in dB), ie dynamic range = USp-p/UNp-p (2) Equation (2) USp-p is the output signal peak voltage.
Therefore, the wide dynamics are particularly bright and particularly dark in the scene, and the wide dynamic range is the ratio of the brightest luminance signal value to the darkest luminance signal value that can be resolved.
Obviously, there are two main methods for determining the dynamic range of the camera imager: one is to use the relevant information of the basic circuit in the sensor and the image processor to be calculated by the above formula; the other is to use the grayscale test card and the experimental instrument. The method of collecting and observing images and measuring image levels is obtained. Although the calculation method can theoretically calculate the limit of the dynamic range, people usually prefer to use the measurement method because it can reflect the user's actual experience of imaging the camera. The following is a detailed introduction to the actual test methods of the dynamic range of the camera by the three foreign manufacturers.
JVC dynamic range test method
The test method for the dynamic range of the camera may be different, but the test principle is similar. Here is a basic test method for JVC:
Equipment and conditions required to test the dynamic range of the camera The equipment required to test the dynamic range of the camera is as follows:
· Transmitted gray card and reflected gray card;
· Backlight box with adjustable brightness and illumination source with adjustable brightness;
· Video monitor and waveform monitor;
· a light meter or illuminometer;
· Standard internal lens, etc.
Conditions for testing the dynamic range of the camera: need to be performed in a dark room.
Basic methods and steps for testing the dynamic range of a camera
· The first step: install two sets of double-order grayscale test cards on the same vertical plane of a table in the darkroom. One set of transmission grayscale cards uses a backlight source with adjustable brightness as a constant reference to adjust the brightness of the backlight to ensure self-determination. The front center confirms that the divergence illuminance of the white block surface is 2500Lx; the other set of reflected gray scale cards adopts an adjustable illumination source on the front side thereof for determining the critical value of the dynamic range;
·Second step: set the height of the camera to be tested and the center of the gray test card to the same level, and maintain an angle of 90° with the vertical plane of the gray test card. At the same time, the camera lens angle can cover 2 sets of gray test cards;
· Step 3: Connect the camera's output signal to the video monitor and waveform monitor;
Step 4: After the camera is powered up, turn on the extended dynamic range function to adjust the brightness of the front illumination source to 2500Lx. Obviously, under this illuminance, it is overexposed (the standard illumination of the factory is 2000Lx). At this time, the white end stripe of the reflected gray card may have a layered mixture, that is, two or more gray bars show the same White, without distinguishing the difference in brightness;
Step 5: Continue to slowly reduce the brightness of the light source, and continuously observe and record the top level of the reflected gray test card waveform from the waveform monitor. When the top level starts to decrease correspondingly due to the decrease of the illumination of the light source, the illuminance value (such as L1) at this time is recorded, and the illuminance value is the upper limit of the dynamic range of the camera. The camera at this time should just show the difference in brightness level between the white stripes with large brightness;
• Step 6: Then continue to slowly reduce the brightness and continuously observe and record the top level of the reflected gray test card waveform from the waveform monitor. When the top level is no longer continuously reduced due to the decrease of the illumination of the light source, the illuminance value (such as L2) at this time is recorded, and the illuminance value is the lower limit of the dynamic range of the camera. At this time, the brightness level difference between the two gray-black stripes of the darkness in the gray card image taken by the camera should just disappear and be mixed into one black.
JEITA's dynamic range test method
Test Results Calculation The formula for calculating the dynamic range using the above actual test method is as follows:
Dynamic range=20logL1/L2(dB)(3) The top level change of JVC's CCD wide dynamic camera TK-WD310EC measured by the above test method starts from 2200Lx to 1.1Lx, and the dynamic range is obtained by formula (2)= 20log2200/1.1=66dB
Using the above test method to measure the top level change of a company's CCD wide dynamic camera from 1500Lx to the end of 5Lx dynamic range is dynamic range = 20log1500/5 = 49dB
JEITA is the abbreviation of Japan Electronic Information Technology Industry Association. Its measurement method for camera dynamic range also uses grayscale test card. In fact, whether an accurate determination of the dynamic range is an important limiting factor is whether the grayscale test card can effectively measure the full value of the dynamic range. For example, the KodakQ-14 test card, the scale difference of adjacent gray scales is 1/3 aperture series (f-stop), and can only measure the dynamic range of 5.66 or about 34 decibels at most.
When using the JEITA method to measure the dynamic range and dynamic range expansion ratio, the gamma value of the grayscale test card is specified as 2.2, with a total of ten grayscale levels, and the dynamic range that can be measured is basically the same as that of the Q-14 grayscale test card. According to the specification of this method, two gray scale test cards are placed side by side with the screen separated by the screen. Then use two different illumination sources to illuminate the test cards on both sides of the screen, as shown in Figure 2.
The JEITA method stipulates that the brighter end of the test card continuously increases the illumination intensity or increases the aperture until it can distinguish the two brightest gray levels, and then continuously reduces the illumination intensity to the darker end of the test card until the most The bright grayscale level (white) reaches 50 IRE. The expansion ratio (dB) of the dynamic range can be calculated by the formula (3) in the aforementioned test method, that is, the dynamic range expansion ratio (dB) = 20 log (L3/L4)
Although this method calculates the dynamic range extension value, it completely ignores the ability of the imager to capture midtones. The JEITA method does not overcome the major drawbacks of double exposure CCD sensors because the method focuses only on the distinction between different grayscale values ​​within the higher and lower tonal ranges.
The drawback of the JEITA method is that all test devices are not explicitly specified; there is no indication of how to place the lighting, what type of light to use, or even how to accurately measure the intensity of the illumination. This means that changes in the experimental setup and measurement conditions will affect the final measurement. It is worth noting that the JEITA method measures the dynamic range extension value rather than the overall measurement range because the method does not specify how to determine the reference dynamic range or the overall dynamic range.
Pixim's dynamic range measurement method
In order to eliminate the above defects, the measurement experiment is reproducible, so that all the tone levels can be observed and compared simultaneously during the measurement process. Pixim uses a customized instrument to measure the dynamic range. The unit includes a light box that uses a 700 watt incandescent light to backlight the light-transmissive stepper card. The step wedges used in the measurement are produced by SinePatterns LLC, and the two wedges are overlapped to a maximum density range of 0.1 to 6.1 or approximately 120 decibels.
It's not easy to accurately display a wide dynamic scene on a computer monitor or in a printed document, but PiximDPS technology captures ultra-wide motion images while presenting monotonous grayscale and intermediate grayscale responses.
The same picture taken by the CCD camera using the double exposure method, please note that although the camera claims to have a high dynamic range, it is actually possible to blur the scene from the highlights of the scene and the crosstone of the midtones. See its obvious limitations. In addition, the response of the camera to the midtones is too flat, compared with the monotonous response of the PiximDPS camera, who is better and worse, at a glance.
Conclusion
The concept of dynamic range and three specific test methods are introduced above, which can be used by users for reference. Looking at the wide dynamic performance of the two cameras they tested, CCD wide dynamic cameras are not as good as CMOS wide dynamic cameras. Although the CCD has high sensitivity, but the response speed is low, it is not suitable for high-resolution progressive scanning mode adopted by high-definition surveillance cameras. Therefore, high-definition surveillance cameras mostly use CMOS imaging devices. And because of its wide dynamic range, high-speed digital readout, no-row readout noise or fixed pattern noise, faster operation speed and lower power consumption, CMOS imaging devices make it easier to implement networking and intelligence. Turn. Obviously, the CMOS camera has great potential, and its excellent performance in terms of dynamic range, etc., will gradually replace the CCD camera and occupy the market in the future.
Since the natural light is arranged from 120,000 Lux to 0.00035 Lux in the night of the starlight, the indoor illumination is 100 Lux, and the illumination of the outside scenery may be 10000 Lux. Therefore, when the camera looks out of the window from the inside, the contrast between the two is 10000/100=100:1. This contrast can be easily seen by the human eye because the human eye can handle a contrast ratio of 1000:1, but the traditional security surveillance camera does not, because it only has a 3:1 contrast performance. Therefore, when a security surveillance camera is applied to a scene with a large contrast or backlight, the exposed areas of the entire image are overexposed and the dark areas are underexposed, and the brightest and darkest parts of the image are not visible.
Such as in bank depositories, entrances and exits of important places, etc. Because the glare from the window and the soft light from the fluorescent light on the ceiling may make it difficult to capture the indoor and outdoor scenes at the time, it is impossible to clearly capture the indoor and outdoor scenes with great contrast. The image taken may have a background that is too bright and the foreground is too dark, or the background is clear and the foreground is too dark and the foreground is suitable for the background to be too bright. The earliest solution, generally using backlight compensation technology or erecting two cameras indoors and outdoors to adapt to large light contrast, but the effect is not satisfactory. The technology to extend the dynamic range has emerged, which is the wide dynamic WDR (WideDynamicRange) technology.
Basic concept of camera dynamic range
The CCD wide dynamic technology uses a special DSP (digital signal processing) circuit to perform the most appropriate shutter speed exposure for the bright portion, and then exposes the dark portion to the most suitable shutter speed, and then performs two DSP processing on the image. Combine so that both the bright part and the dark part can be seen clearly. Although the 160-fold dynamic range technology has the advantages of large wide dynamics and optimization of image grayscale, it requires high DSP performance (especially processing speed). At present, due to the limitations of the CCD, even with multiple exposure sampling, the camera's wide dynamic range can only reach 66dB.
Obviously, due to the limitation of the photographic characteristics of the CCD, it is technically difficult to make a major breakthrough, and the CMOS camera has outstanding performance due to its excellent performance. For example, the linear range of the general linear output mode can reach 40~60dB; the D28 of the IM28-SA type CMOS camera with linear-logarithmic output mode in Canada can have a dynamic range of up to 120dB; Apical Co., Ltd. combines Altera's CycloneIII and CycloneIVFPGA, using the AptinaMT9M033720pWDRCMOS image sensor, also introduced a CMOS wide dynamic camera with both bright and dark parts visible; PIXIM USA developed CMOS-DPS technology, and its chipset has performance from D1000, D1500, D2000 to D2500. The speed is improved: the image sharpness is increased from 480 lines to more than 540 lines; the minimum illumination is from 1.0Lux/F1.2 to 0.5Lux/F1.2; the typical wide dynamic range is from 95dB to 120dB. According to the news, some CMOS wide dynamic technologies have even reached 160dB. Therefore, it is foreseeable that future surveillance cameras belong to wide dynamic cameras, while wide dynamic technology belongs to CMOS.
At present, in the global market, there are about 100 types of wide dynamic cameras in more than 50 countries put into practical use, but most of the camera manufacturers use Pixim's DPS technology. This is because the core technology of the DPS chip is to have an ADC in every pixel. That is, at an accurate capture point, the optical signal is converted into a digital signal. The benefit of this is that there is no crosstalk between pixels and no signal loss.
Basic concept of camera dynamic range
The so-called wide dynamic reality means that the camera can simultaneously see the illuminance ratio of the brightest and darkest parts of the image. The "dynamic range" refers broadly to the span that a change thing may change, that is, the region between the lowest pole and the highest pole of the change value. The description of this region is generally between the highest point and the lowest point. Difference. The “dynamic range†of the camera refers to the ability of the camera to adapt to the illumination of the scene in the scene, specifically the range of brightness (contrast) and color temperature (contrast). This means that the camera's most "dark" and "bright" adjustment range for the image is the ratio of the brightest to darkest tones in a still image or video frame. The hue can show the precise details in the image or frame. As the ratio of the two tones, the unit of dynamic range can be decibel, bit, file, or simply expressed as a ratio or multiple. The conversion method between various units is shown in Table 1.
The 20-speed dynamic range is listed because it covers almost all the dynamic range that the human eye can distinguish. The dynamic range beyond these gears has little practical significance. The reason why the human eye can distinguish such a wide dynamic range is because when people observe the real scene, the pupil, iris, retina and related muscles interact and dynamically adjust. At the same time, the brain integrates all the "exposure elements" into A coherent image that reflects the very bright or very dull tones of the real scene with extreme precision.
JVC dynamic range test method
Compared to the human eye, for standard CCD and CMOS image sensors, the exposure (collecting photons) time of all photosensitive cells is the same. The photosensitive unit collects more photons for the bright part of the scene, and fewer photons for the dark part. However, the number of photons that the photosensitive unit can collect is limited by the wellcapacity, so that the photosensitive unit that captures the brighter color of the object may overflow or saturate. To prevent this from happening, you can reduce the exposure time. However, if you do this, the photosensitive unit that captures the darker tones of the object may not be able to collect enough photons. Therefore, for a typical single exposure image sensor, the upper limit of the dynamic range is limited by the well capacity of the photosensitive unit, and the lower limit is limited by the signal to noise ratio of the photosensitive unit. Thus, the dynamic range of the CCD image pickup device under the peak noise refers to a saturated output voltage and dark field - the ratio of peak voltage, i.e. the dynamic range <br> <br> = Usat / UNp-p (1 )
In the formula (1), Usat is the output saturation voltage; UNP-P is the peak-to-peak value of the noise.
Obviously, the dynamic range can also be defined and calculated as the ratio of the maximum amount of charge that can be stored in the CCD well and the amount of charge determined by the noise; the value is also the signal peak voltage and the rms noise voltage at the output. Ratio (usually expressed in dB), ie dynamic range = USp-p/UNp-p (2) Equation (2) USp-p is the output signal peak voltage.
Therefore, the wide dynamics are particularly bright and particularly dark in the scene, and the wide dynamic range is the ratio of the brightest luminance signal value to the darkest luminance signal value that can be resolved.
Obviously, there are two main methods for determining the dynamic range of the camera imager: one is to use the relevant information of the basic circuit in the sensor and the image processor to be calculated by the above formula; the other is to use the grayscale test card and the experimental instrument. The method of collecting and observing images and measuring image levels is obtained. Although the calculation method can theoretically calculate the limit of the dynamic range, people usually prefer to use the measurement method because it can reflect the user's actual experience of imaging the camera. The following is a detailed introduction to the actual test methods of the dynamic range of the camera by the three foreign manufacturers.
JVC dynamic range test method
The test method for the dynamic range of the camera may be different, but the test principle is similar. Here is a basic test method for JVC:
Equipment and conditions required to test the dynamic range of the camera The equipment required to test the dynamic range of the camera is as follows:
· Transmitted gray card and reflected gray card;
· Backlight box with adjustable brightness and illumination source with adjustable brightness;
· Video monitor and waveform monitor;
· a light meter or illuminometer;
· Standard internal lens, etc.
Conditions for testing the dynamic range of the camera: need to be performed in a dark room.
Basic methods and steps for testing the dynamic range of a camera
· The first step: install two sets of double-order grayscale test cards on the same vertical plane of a table in the darkroom. One set of transmission grayscale cards uses a backlight source with adjustable brightness as a constant reference to adjust the brightness of the backlight to ensure self-determination. The front center confirms that the divergence illuminance of the white block surface is 2500Lx; the other set of reflected gray scale cards adopts an adjustable illumination source on the front side thereof for determining the critical value of the dynamic range;
·Second step: set the height of the camera to be tested and the center of the gray test card to the same level, and maintain an angle of 90° with the vertical plane of the gray test card. At the same time, the camera lens angle can cover 2 sets of gray test cards;
· Step 3: Connect the camera's output signal to the video monitor and waveform monitor;
Step 4: After the camera is powered up, turn on the extended dynamic range function to adjust the brightness of the front illumination source to 2500Lx. Obviously, under this illuminance, it is overexposed (the standard illumination of the factory is 2000Lx). At this time, the white end stripe of the reflected gray card may have a layered mixture, that is, two or more gray bars show the same White, without distinguishing the difference in brightness;
Step 5: Continue to slowly reduce the brightness of the light source, and continuously observe and record the top level of the reflected gray test card waveform from the waveform monitor. When the top level starts to decrease correspondingly due to the decrease of the illumination of the light source, the illuminance value (such as L1) at this time is recorded, and the illuminance value is the upper limit of the dynamic range of the camera. The camera at this time should just show the difference in brightness level between the white stripes with large brightness;
• Step 6: Then continue to slowly reduce the brightness and continuously observe and record the top level of the reflected gray test card waveform from the waveform monitor. When the top level is no longer continuously reduced due to the decrease of the illumination of the light source, the illuminance value (such as L2) at this time is recorded, and the illuminance value is the lower limit of the dynamic range of the camera. At this time, the brightness level difference between the two gray-black stripes of the darkness in the gray card image taken by the camera should just disappear and be mixed into one black.
JEITA's dynamic range test method
Test Results Calculation The formula for calculating the dynamic range using the above actual test method is as follows:
Dynamic range=20logL1/L2(dB)(3) The top level change of JVC's CCD wide dynamic camera TK-WD310EC measured by the above test method starts from 2200Lx to 1.1Lx, and the dynamic range is obtained by formula (2)= 20log2200/1.1=66dB
Using the above test method to measure the top level change of a company's CCD wide dynamic camera from 1500Lx to the end of 5Lx dynamic range is dynamic range = 20log1500/5 = 49dB
JEITA is the abbreviation of Japan Electronic Information Technology Industry Association. Its measurement method for camera dynamic range also uses grayscale test card. In fact, whether an accurate determination of the dynamic range is an important limiting factor is whether the grayscale test card can effectively measure the full value of the dynamic range. For example, the KodakQ-14 test card, the scale difference of adjacent gray scales is 1/3 aperture series (f-stop), and can only measure the dynamic range of 5.66 or about 34 decibels at most.
When using the JEITA method to measure the dynamic range and dynamic range expansion ratio, the gamma value of the grayscale test card is specified as 2.2, with a total of ten grayscale levels, and the dynamic range that can be measured is basically the same as that of the Q-14 grayscale test card. According to the specification of this method, two gray scale test cards are placed side by side with the screen separated by the screen. Then use two different illumination sources to illuminate the test cards on both sides of the screen, as shown in Figure 2.
The JEITA method stipulates that the brighter end of the test card continuously increases the illumination intensity or increases the aperture until it can distinguish the two brightest gray levels, and then continuously reduces the illumination intensity to the darker end of the test card until the most The bright grayscale level (white) reaches 50 IRE. The expansion ratio (dB) of the dynamic range can be calculated by the formula (3) in the aforementioned test method, that is, the dynamic range expansion ratio (dB) = 20 log (L3/L4)
Although this method calculates the dynamic range extension value, it completely ignores the ability of the imager to capture midtones. The JEITA method does not overcome the major drawbacks of double exposure CCD sensors because the method focuses only on the distinction between different grayscale values ​​within the higher and lower tonal ranges.
The drawback of the JEITA method is that all test devices are not explicitly specified; there is no indication of how to place the lighting, what type of light to use, or even how to accurately measure the intensity of the illumination. This means that changes in the experimental setup and measurement conditions will affect the final measurement. It is worth noting that the JEITA method measures the dynamic range extension value rather than the overall measurement range because the method does not specify how to determine the reference dynamic range or the overall dynamic range.
Pixim's dynamic range measurement method
In order to eliminate the above defects, the measurement experiment is reproducible, so that all the tone levels can be observed and compared simultaneously during the measurement process. Pixim uses a customized instrument to measure the dynamic range. The unit includes a light box that uses a 700 watt incandescent light to backlight the light-transmissive stepper card. The step wedges used in the measurement are produced by SinePatterns LLC, and the two wedges are overlapped to a maximum density range of 0.1 to 6.1 or approximately 120 decibels.
It's not easy to accurately display a wide dynamic scene on a computer monitor or in a printed document, but PiximDPS technology captures ultra-wide motion images while presenting monotonous grayscale and intermediate grayscale responses.
The same picture taken by the CCD camera using the double exposure method, please note that although the camera claims to have a high dynamic range, it is actually possible to blur the scene from the highlights of the scene and the crosstone of the midtones. See its obvious limitations. In addition, the response of the camera to the midtones is too flat, compared with the monotonous response of the PiximDPS camera, who is better and worse, at a glance.
Conclusion
The concept of dynamic range and three specific test methods are introduced above, which can be used by users for reference. Looking at the wide dynamic performance of the two cameras they tested, CCD wide dynamic cameras are not as good as CMOS wide dynamic cameras. Although the CCD has high sensitivity, but the response speed is low, it is not suitable for high-resolution progressive scanning mode adopted by high-definition surveillance cameras. Therefore, high-definition surveillance cameras mostly use CMOS imaging devices. And because of its wide dynamic range, high-speed digital readout, no-row readout noise or fixed pattern noise, faster operation speed and lower power consumption, CMOS imaging devices make it easier to implement networking and intelligence. Turn. Obviously, the CMOS camera has great potential, and its excellent performance in terms of dynamic range, etc., will gradually replace the CCD camera and occupy the market in the future.
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