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ISP image processing 3A technology

Sep 10, 2017

wifi security camera

ISP image processing 3A technology

3A technology is auto focus (AF), automatic exposure (AE) and automatic white balance (AWB). 3A digital imaging technology using the AF AF algorithm, AE automatic exposure algorithm and AWB automatic white balance algorithm to achieve the largest image contrast, improve the subject of the subject over-exposure or exposure to the situation, so that the screen in different light irradiation under the color difference is compensated, Thereby presenting a higher quality image information. Using 3A digital imaging technology camera can be a good guarantee image accurate color reproduction, showing the perfect day and night monitoring effect.


Autofocus algorithm (AF)


    Is through the vested image contrast to move the lens to maximize the image contrast. In general, autofocus technology is to adjust the focus of the lens position to obtain the highest image frequency components, get a higher image contrast. Among them, to obtain the best focus is a constant accumulation of the process, which by comparing the contrast of each frame image to obtain the maximum range of motion within the lens point, and then determine the focus distance.


    The highest image frequency component is obtained by adjusting the position of the focus lens. In general, the focus picture has a higher contrast ratio than the focus picture contains a higher frequency component, that is, the corresponding picture has a higher contrast. Getting the best focus is a constant accumulation process that determines the focus distance by comparing the contrast of each frame to obtain the maximum contrast point within the lens movement range. The popular autofocus system now uses hill-climbing. However, the algorithm also has some limitations, it only applies to the larger image itself, the situation of large color.


    The traditional camera, taking a similar visual distance measurement to achieve auto focus, the camera launches an infrared (or other rays), according to the object to determine the distance of the subject, and then adjust the lens combination based on the measured results, To achieve autofocus. This autofocus mode - direct, fast, easy to implement, low cost, but sometimes error (the camera and the subject have other things such as glass can not achieve auto focus, or in the case of lack of light ), The accuracy is poor, and now high-end camera generally do not use this way. Because the camera is the initiative to launch radiation, so that active, but also because it is actually only ranging, not through the actual image of the lens to determine whether the correct coking, it is also known as non-TTL. This focus mode relative to the active auto focus, and later developed a passive autofocus, that is, according to the actual image of the lens to determine whether the correct coking, the basis of judgment is generally contrast detection, the specific principle is quite complex. Because this way is achieved through the lens imaging, so called TTL auto focus. It is also because of this type of autofocus based on the lens imaging to achieve, so the focus is high, the error rate is low, but the technology is complex, slower (except for the use of ultrasonic motor high-focus lens), the cost is higher. Manual focus, it is by manually rotating the focus ring to adjust the camera lens so that the picture taken out clearly a focus mode, this way a large degree of dependence on the human eye on the focus screen image recognition and photographers skilled The degree of even the photographer's eyesight. Early SLR cameras and paraxial cameras are basically using manual focus to complete the focus operation. Now the quasi-professional and professional digital cameras, as well as SLR digital cameras are equipped with manual focus function to meet the needs of different shooting.


    Automatic Exposure Algorithm (AE)


    The exposure value is automatically set according to the available light source conditions. When the subject of the subject and the background of the brightness difference is very large, the general subject will cause the subject of exposure or exposure, in order to overcome this problem, some specific AE algorithm focused on the subject of the brightness of the subject, in the brightness adjustment When giving this part more proportion.


    In the program auto exposure mode, the camera can automatically set the shutter speed and aperture value according to the exposure value of the subject screen measured by the metering system according to the shutter and aperture exposure combination set by the manufacturer. In terms of camera operability, in this way the equivalent of the so-called "fool camera", the operator does not have to adjust the shutter speed and aperture value, all you have to do is focus on the focus, press the shutter release button on the line. In the "fool" camera common electronic program shutter, it belongs to this exposure mode. In fact, only the program automatically exposing the way is the real "automatic" exposure.


    Automatic White Balance Algorithm (AWB)


    Adjust the fidelity of the picture color according to the light source condition. Objects in different light exposure will appear under varying degrees of color, the general image of an image of the overall color difference signal used as color temperature data, when most of the image area is covered by a uniform color, this color compensation may be lost Part of the complete color. To compensate for this flaw, some specific AWB algorithms have been proposed to accommodate different color temperature conditions.


    White balance English name for White Balance. The color of the object will change due to the projected light color, in different light occasions, the photos taken will have different color temperature. For example, the tungsten lamp (light bulb) lighting the environment to shoot the photos may be yellow, in general, CCD no way like the human eye will automatically correct the light changes. The following pictures show different images in different colors. Balance is no matter how the ambient light, so that the default digital camera "white" is to let him recognize the white, and balance its color in colored tones under the color. The color is essentially the interpretation of light, in normal light looks white color things in the darker light may not look white, there are fluorescent under the "white" is "non-white". For all this if you can adjust the white balance, in the resulting photos will be able to "white" as the primary color to restore other colors. Most commercial grade digital cameras now offer white balance adjustment. As mentioned earlier, the white balance is closely related to the surrounding light, so the use of the flash function is limited when the white balance function is activated, otherwise the change in ambient light will cause the white balance to fail or interfere with the normal white balance. General balance has a variety of modes to adapt to different scenes, such as: automatic white balance, tungsten white balance, fluorescent white balance, indoor white balance, manual adjustment.


    Interpreting the surveillance camera 3A algorithm


    For the above mentioned 3A algorithm, the following for everyone to do an in-depth interpretation. Which automatic white balance (AWB) algorithm is mostly used in the field of digital camera, with the same capture image function of the surveillance camera, AWB will play what role? First, the AWB is used to correct the color distortion that causes color temperature changes.


    For example, because the color temperature is low, the image sensor captures the dusk in the yellow tones, and in the sunny environment, will show a high blue tones. Using these algorithms, analog cameras not only shoot better images in low light conditions, but also provide better color reproduction and color compensation.



Monitoring camera automatic exposure is carried out in stages, automatic exposure control and lens iris were able to show a more perfect image. With the external ambient light from the bright case, the entire exposure step is divided into five steps, the final activities of color, black and white, brightness and color moderate image. In simple terms, automatic exposure controls the brightness of the image automatically adjusted.


     The autofocus function is well understood, and by adjusting the position of the focused lens to obtain the highest image frequency component, the auto white balance compensates for the chromatic aberration caused by the different light. 3A imaging control algorithm for the camera imaging results have a crucial impact. Whether it is in the early morning or evening, or light complex night environment, can not be taken from the viewfinder, light and shadow effects, to provide accurate color reduction, showing the perfect day and night monitoring effect.

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