Camera sensitivity mode

Color

ExView

Number of pixels

Resolution (LPH)

Subpanels:

Minimum scene illumination

Min. illum. (lx)

AT:

Aperture

S/N (dB)

IRE

Exposure (ms)

Signal/noise ratio

S/N max.

S/N current

S/N C>B/W

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+

Digital control of modern cameras can significantly increase the signal-to-noise ratio at the cost of losses in overall resolution or resolution of moving objects. But the signal-to-noise ratio is used as a criterion of image quality when measuring the minimum illumination (sensitivity) of a camera.

If 2D and 3D noise reduction (2DNR 3DNR) mode and / or Pixel Binning are turned on in a camera, the result of measuring the minimum illumination may be several times less than when the digital control of the camera is turned off.

However, 2D noise reduction improves the appearance of an image, but does not increase its informativeness. 3D noise reduction reduces noise only on fixed objects. Pixel Binning leads to a deterioration in the overall resolution in several times. In case of inattentive examination, these image defects can be overlooked.

For correct assessment and comparison of sensitivity, the Camera sensitivity mode parameter may contain a short description of the operation mode in which the camera shows the claimed minimum scene illumination value.

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;

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;

IR illumination is also modeled for Easy Day/Night cameras (without a movable IR filter), since this type of camera can be with a constant IR filter and without an IR filter, often the implementation of the day/night mode is not clear from the camera specification.

At illumination reduction day/night and easy day/night cameras are switched into black-white mode. At the same time their sensitivity becomes equal to the value in the Minimum scene illumination>B/W mode box.

The S/N C>B/W parameter determines the signal-to-noise ratio at which the day/night and easy day/night cameras switch to black/white mode.

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.

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.

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.

The button with an arrow between the boxes is designed to quickly calculate the number of pixels vertically with the entered number of pixels horizontally and vice versa. The calculation is carried out through the Aspect Ratio of the frame.

The button with two arrows between the boxes is designed to quickly swap the number of pixels horizontally and vertically.

The number of active pixels is duplicated in the Camera Geometry box.

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 (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 you can enter 2 values of the minimum illumination: in color and black and white modes.

The S/N C>B/W parameter determines the signal-to-noise ratio at which the day/night and easy day/night cameras switch to black/white mode.

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

To allow lens contamination, dirt, camera degradation and parameter variation it is necessary to set maintenance factor of cameras on the Illumination 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 , Camera sensitivity mode

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.

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 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.

The IRE value in this box is specified with the gamma correction specified in the Degree of gamma correction box (even if the Gamma checkbox is not checked!).

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

Parameter is sometimes given in camera specifications.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.

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.

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.

The signal-to-noise ratio of the simulated image, upon reaching which, as a result of a decrease in illumination, the day/night and easy day/night cameras switch to black/white mode.

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

Exposure time limits within which electronic shutter operates.

The parameter is given in camera's specification.  For IP cameras the maximum exposure time can be larger, up to several seconds.

To set the maximum exposure time to more than 1 second, enter a value with a dot, for example:

2 = 1/2 second;

2.0 = 2 seconds.

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.

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.

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 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.

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.

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.

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.

In the box you can choose:

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.

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!).

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.