VideoCAD

Sensitivity and Resolution

 Camera

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Sensitivity and Resolution

 Camera

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Sensitivity and Resolution

 Camera

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Color

ExView

Number of pixels

Resolution (LPH)

 

Subpanels:

 

Minimum scene illumination

 

Min. illum. (lx)

AT:

Aperture

S/N (dB)

IRE

Exposure (ms)

On sensor

 

Signal/noise ratio

 

S/N max.

S/N current

 

Electronic shutter (ES, AES, AESC, shutter)

 

AESC

Exposure time limits (shutter speed, shutter LIM, SPD)

Current

- Level+

Automatic gain control (AGC)

 

AGC

Current

Maximum

Set

 

Back light compensation (BLC)

 

BLC

BLC type

 

Gamma

 

Gamma

Degree of gamma correction

 

Internal Auto iris amplifier DC (DD)

 

Auto Iris DC -Level+

 

 


Color

 

In the box camera color can be chosen. 4 variants are available:

 

B/W - black-white camera;

 

color - color camera;

 

day/night - full day/night camera, which has infra-red filter that is mechanically removed in black-white mode;

in black-white mode the day/night camera is sensitive to infrared light;

day/night camera at sufficient illumination behaves as a color camera with sensitivity approximately in 5 times less than in black-white mode;

 

easy day/night - camera has infra-red filter which is not removed in black-white mode;

easy day/night camera have much less advantages in sensitivity from switching to black-white mode, than full day/night cameras have;

in black-white mode easy day/night camera is non sensitive to infrared light;

At sufficient illumination easy day/night camera behaves as color camera with the sensitivity approximately in 2 times less than in black-white mode.

 

At illumination reduction day/night and easy day/night cameras are switched into black-white mode. At the same time their sensitivity increases up to the value set on Minimum scene illumination panel.

 

Color parameter influences 3D model color as well as spectral sensitivity of cameras to various light sourses.

For example, color camera is non sensitive to IR illumitators, and black-white camera has reduced sensitivity to light of discharge lamps in comparison with Incandescent lamp.

 

ExView

 

In the camera image sensor with increased relative IR sensitivity is used.

Image sensor type is usually specified in camera specification.

 

Image sensor type influences spectral efficiency factors of different light sources that are used in modeling. However this influence does not exceed 15-20 %. Do not mark this box if the type of image sensor is unknown.

 

Though Sony ExView HAD ™ CCD has increased total sensitivity, this box does not influence sensitivity to illumination produced by Halogen Incandescent lamps. Sensitivity to Halogen Incandescent lamps is unequivocally specified in the Min. illum. (lx) box.

 

Number of pixels

 

In the combo boxes you can choose horizontal and vertical numbers of effective pixels on the image sensor. Analog cameras have, as a rule, 752x582 (high resolution) or 500x582 (standard resolution) effective pixels.

Number of effective pixels of IP cameras can be different.

 

If N/A is chosen in the box, then number of pixels is not considered.

 

In the boxes exactly the number of image sensor's pixels is to be specified, without considering analog-to-digital conversion or output image size. Analog-to-digital conversion or output image size is set on the Processing tab of the Image parameter panel. The final image is modeled considering distortions connected with different number of pixels on image sensor and in output image.

 

A button with a cross between combo boxes with horizontal and vertical numbers of pixels is intended for fast calculation of vertical number of pixels from the specified horizontal number of pixels and on the contrary. Calculation is carried out using the Aspect Ratio.

 

Criteria of person detection, identification and license plate reading, spatial resolution depend on the number of pixel. Therefore the number of pixels influences person detection, identification and license plate reading areas, positions of spatial resolution regions and image examples in the Spatial resolution box.

For criteria calculation minimal number of pixels from parameters of camera image sensor and parameters of output image is used.

Number of pixels of output image is specified on the Processing tab of the Image parameter panel.

If number of pixels is not set (N/A), calculation is performed for vertical 576 pixels (or horizontal 768 pixels), what corresponds to analog camera.

 

If a camera is rotated around its axis by an angle more than 45 degrees, when calculating person detection and identification, license plate reading areas,  the parameters: minimum vertical resolution (pixel/meter, pixel/ft), the minimum vertical size of face image ( pixels ), the minimum vertical size of license plate ( pix) are calculated based on the number of pixels along the horizontal, instead of the number of pixels along the vertical, as in this case the vertical side of the field of view is located along the horizontal.

 

When calculating the spatial resolution, rotation of the camera around its axis by default does not affect the position of the vertical and horizontal in the frame.  Horizontal and vertical positions are tied to the camera and not to the scene. You can change this rule, using the Spatial resolution and rotation checkbox in the Options box .

 

The positions of the boundaries of spatial resolution and the sample images in the Spatial resolution box are affected by the number of pixels in vertical or horizontal direction depending on the position of the Vert. / Hor switch in settings of a pattern of spatial resolution, assigned to the camera.

 

Resolution (LPH)

 

In the box you can specify resolution of the active camera, in LPH - Lines per Picture Height. At 3D modeling resolution of image will be limited up to the value set in this box.

In the box on the left, a value of the lines per picture height (LPH) is entered, and in the box on the right a drop of contrast in % according to the MTF at the entered number of lines is specified.

If the Horiz. only checkbox is checked then only horizontal resolution is modeled, which is typical for analog cameras. If the Horiz. only checkbox is not checked, the camera resolution will decrease horizontally and vertically in the same degree.

 

If N/A is chosen in the box, then resolution limitation is disabled.

 

Items sharp+1, sharp+2, sharp+3 on the contrary increase image sharpness. With the help of these items it is possible to model effect of Aperture corrector.

 

Aperture corrector is automatically switched-off at insufficient illumination.

 

You can also simulate the lens resolution. When the lens resolution simulation and camera resolution simulation are both enabled, then their effects are summarized.

 

You can check resolution visually using the Test chart.

 

Minimum scene illumination

Min. illum. (lx)

 

Minimum scene illumination (lux). The parameter is given in specification of any cameras.

 

However usage in calculations and models the minimum illumination values from specification of some manufacturers can lead to errors.

 

In VideoCAD it is meant, that scene reflection factor is 0.75, light source - halogen incandescent lamp (color temperature 3100 +-200K) according to Standard CEA 639 'Consumer Camcorder or Video Camera Low Light Performance'.

 

For day/night and easy day/night cameras in this box it is necessary to enter the minimum scene illumination in black-white mode.

 

For unambiguous description of sensitivity in VideoCAD, should be pointed also:

 

with what lens aperture the minimum illumination is measured;
signal/noise ratio of the image at the minimum illumination;
IRE of video signal at the minimum illumination;
exposure time at what the minimum illumination is measured.

 

To allow lens contamination, dirt, camera degradation and parameter variation it is necessary to set maintenance factor of cameras on the 3D modeling tab of the Options box.

 

For modeling increased contrast at constant signal/noise ratio use parameter Maximum AGC gain.

 

Sometimes the boosted sensitivity is achieved due to noise decreasing as a result of digital image processing. But in this case resolution essentially decreases too.

For modeling resolution decreasing, use Sharpness parameter.

 

See also: About camera sensitivity, Measuring camera sensitivity.

AT:

Aperture

 

Lens aperture at which the minimum scene illumination is measured.

The parameter is given in camera specification. Typical value from F1.0 up to F2.0.

 

S/N (dB)

 

Signal/noise ratio of the image at the minimum illumination, unweighted value.

 

According to CEA 639, limit value of signal/noise ratio at the minimum illumination determination is 17dB (7 times in voltage).

 

IRE

 

IRE of video signal at minimum illumination, at AGC switched on by default.

In VideoCAD 100 IRE corresponds full peak-to-peak amplitude of video signal and accordingly to maximum brightness amplitude on the image. 50IRE corresponds half of maximum brightness amplitude on the image, etc.  

 

The parameter is given in camera's specification. Typical value is from 30 to 50.

 

If Set box is marked (the maximum AGC gain in set), AGC mode does not correspond default AGC mode of camera. It means that IRE value at minimum illumination also will not correspond to the value specified in the IRE box. Therefore this box will be grey.

The more maximum AGC gain is, the larger is IRE.

 

Exposure (ms)

 

Exposure time (milliseconds) at which the minimum illumination has been measured.

Parameter is sometimes given in camera specifications. For analog cameras typically value is 20ms(PAL) or 16.5ms (NTSC). For IP cameras and analog cameras with light accumulation the exposure time may be up to 200ms or more.

VideoCAD offers a technique of measuring exposure time of cameras with an analog oscilloscope, see: Measuring exposure time of IP camera

At modeling the exposure time assumed the truth of the Reciprocity principle, that is inversely proportional of sensitivity to the exposure time.

 

See also: Modeling exposure.

 

On sensor

 

Calculated illumination on the image sensor of the camera, corresponding the minimum illumination of scene with reflection factor 0.75.

 

This parameter is for information only.

 

Signal/noise ratio

 

S/N max.

 

Maximum signal/noise ratio of the camera (dB).

In this box it is necessary to choose weighted value. Normally weighted value of maximum signal/noise ratio is given in cameras' specification.

 

At that it is not specially indicated in specification that just weighted value is given.

 

Typical value for cameras with 1/3 " CCD image sensors is 50dB.

 

If only unweighted value is known, for obtaining the weighted value it is necessary to add 8dB to unweighted one, according to http://cctv-information.co.uk

 

Maximum signal/noise ratio determines dynamic range of camera.

For accurate modeling it is possible to measure maximum scene illumination of the real camera directly, then choose Maximum signal/noise ratio for obtaining equal maximum illumination of the camera model in VideoCAD.

 

S/N current

 

Current signal/noise ratio of the modeling image (unweighted value).

The parameter is calculated during modeling.

 

In the project 2 values are stored: for day time and night time.

 

Electronic shutter (ES, AES, AESC, shutter)

 

AESC

 

Switching on/off electronic shutter. The electronic shutter controls exposure time depending on illumination.

 

Exposure time limits (shutter limits, shutter speed, shutter LIM, SPD)

 

Exposure time limits within which electronic shutter operates.

 

The parameter is given in camera's specification. Modern PAL system cameras have exposure limits 1/50s-1/100000s. For cameras of NTSC system the maximum exposure is 1/60s. For IP cameras the maximum exposure time can be larger, up to several seconds.

 

Current

 

Current exposure time.

If exposure is limited by electronic shutter (electronic shutter operates), the box becomes aqua color.

If current exposure time reaches minimum exposure time, the box becomes yellow together with box, in which minimum exposure time is specified.

 

The parameter is calculated during modeling. In the project 2 values are stored: for day time and night time.

 

At modeling the exposure time assumed the truth of the Reciprocity principle, that is inversely proportional of sensitivity to the exposure time.

 

- Level+

 

Adjuster of electronic shutter sensitivity to illumination change. Visually this adjuster changes contrast of the image, which is obtained as a result of automatic electronic shutter's work. If the contrast is too high, bright areas on the image are white level clipped.

 

The adjustment range of real cameras can be different.

 

Automatic gain control (AGC)

 

AGC

 

Switching AGC on/off. The AGC maintains constant video signal level at its insufficient level by additional gain. At that together with the useful signal the noise is gained too.

 

Current

 

Current AGC gain (dB).

 

The parameter is calculated during modeling. In the project 2 values are stored: for day time and night time.

 

If AGC additionally gains the signal, the box becomes aqua color.

 

If Maximum AGC gain is set and gain value achieves the maximum, the box becomes yellow, together with Maximum AGC gain box and IRE box.

 

Maximum

 

In this box it is possible to specify Maximum AGC gain (dB) for cameras with switchable AGC gain: High AGC gain (High AGC, S-AGC, Super AGC) or LO AGC gain.

The box will be enabled and the set AGC limit will be considered in modeling, if the Set box is marked.

Enter in the box maximum AGC gain if it is given in the camera's specification.

 

Typical value is 26-42dB.

 

If the camera does not have switchable AGC gain, the box must be disabled, and the maximum AGC gain is calculated in the program.

 

Set

 

Switch ON the specified maximum AGC gain. If this box is marked, the maximum AGC gain set in the Maximum box is used in calculation.

 

The check mark in this box means that a special AGC mode is switched on.

 

If this box is marked, the AGC mode is not corresponding to default camera's AGC mode. That means that the IRE value at minimum illumination also will not correspond to the value specified in the IRE box. Therefore the IRE box becomes grey.

The more maximum AGC gain is, the larger is IRE.

 

The signal/noise ratio depends only a little on the AGC gain.

 

Back light compensation (BLC)

 

BLC

 

Switching on/off back light compensation (BLC). If this function is switched on, measurement of image brightness for the electronic shutter or Auto Iris (DC only) adjusting is made not by full image, but only by central or central and lower parts of it.

This function allows to view objects at image centre which are on different brightness background.

 

BLC type

 

In the box you can choose:

 

Center - analyze brightness on image center;

Multizone - analyze brightness on center and bottom of the image.

 

Gamma

Gamma

 

Switching on/off gamma correction. Gamma correction is used in the majority of cameras by default. The correction of the linear response of a camera in order to compensate for the monitor phosphor screen non-linear response. Visually, at switched on gamma correction dark areas of an image become visible better, but contrast of bright areas decreases.

 

Degree of gamma correction

 

The parameter is given in cameras' specification. Normally gamma correction degree equals 0.45. The degree equal 1 is equivalent to absence of gamma correction.

 

It is supposed, that measurement of minimum illumination is performed at the gamma correction degree set in this box (even if the Gamma box is not marked!).

 

Internal  Auto iris amplifier DC (DD)

 

Auto Iris DC -Level+

 

Adjuster of Auto Iris DC gain. The slider corresponds to a similar adjuster on camera's case. Visually this adjuster changes image contrast which is achieved as a result of auto iris adjustment. If the contrast is too high, bright areas on the image are white level clipped.

 

Adjustment range of real cameras can be different.