Revision as of 15:32, 9 April 2013

Introduction

The DM365 and DM368 support the H3A hardware accelerator for supporting auto white balance (AWB) and auto exposure (AE). CMOS or CCD sensor video capture quality can be enhanced with AWB and AE image processing:

Auto exposure performs automatic adjustments of the image brightness according to the amount of light that reaches the camera sensor.
Auto white balance automatically compensates color differences based on lighting so white actually appears white.

Some camera sensors don't include auto white balance and/or auto exposure processing, so RidgeRun offers a library with AE and AWB algorithms called librraew. This library was initially developed for the DM365/DM368 (DM36x) platform. The DM36x video processing front end (VPFE) has an H3A engine designed to support control loops for auto focus, auto white balance and auto exposure by collecting statistics about the imaging/video data. There are two blocks in this module:

Auto focus engine
Auto exposure and auto white balance engine

The librraew library only uses the auto exposure and auto white balance hardware engine which requires the video frames to be in the Bayer color space. The DM36x does not allow the H3A engine to be used when the color space is YCbCr, which is common if you are using NTSC/PAL composite video input.

The H3A engine divides the frames into two dimensional blocks of pixels referred as windows. The engine provides image/video metrics:

Accumulation of clipped pixels along with all non-saturated pixels in each window on a per color basis.
Accumulation of the sum of squared pixels per color.
Minimum and maximum pixels values in each window on a per color basis.

The DM36x H3A engine can be configured to use up to 36 horizontal windows with sum + {sum of squares or min+max} output or up to 56 horizontal windows with sum output. The H3A engine can also be configure to use up to 128 vertical windows. The width and height for the windows is programmable.

The librraew library was tested using an Aptina MT9P031 CMOS sensor. Support for other sensors was added later, thus validating the librraew design. If you provide the appropriate sensor-specific functions for the library, it can work with any sensor. The implementation is a plain C library and can be re-used with and integrated with any application capable of making C function calls. Image Pipe Daemon uses librraew to provide auto exposure/Auto white balance.

License

Evaluation and Development License

Subject to the terms and conditions of RidgeRun's SDK license, RidgeRun hereby grants to customer a product - based, non - exclusive, non - transferable, non - sublicensable, limited, worldwide license to install and use, for internal purposes only, an unlimited number of copies of the source and object code versions.

Distribution License

Subject to the terms and conditions of RidgeRun's SDK license, RidgeRun hereby grants to customer a non-exclusive, non-transferable, non-sublicensable, limited, worldwide license to distribute RidgeRun Software in object code format only (no source code) in one product model sold by the customer.

Limitations

There are some not-so-obvious limitations when using the H3A engine:

AWB/AE correction limited to window sampling method listed above.
Can not use H3A engine with YCbCr color space, which includes NTSC/PAL composite video input.
Auto exposure can affect the video frame rate with dark images. Set a maximum exposure limit to keep the frame rate from dropping below an acceptable value.
Only tested with Linux 2.6.32 and the RidgeRun MT9P031 V4L2 driver.

Algorithms

Auto white balance

When an image of a scene is captured by a digital camera sensor, the sensor response at each pixel depends on the scene illumination. Depending of the illumination, a distinct color cast appears over the captured scene. This effect appears in the captured image due to the color temperature of the light. If a white object is illuminated with a low color temperature light source, the object in the captured image will have a reddish tint. Similarly, when the white object is illuminated with a high color temperature light source, the object in the captured image will appear somewhat blue instead of pure white. The human eye compensates for color cast automatically through a characteristic known as color constancy, allowing the colors to be independent of the illumination. Auto white balance tries to simulate the color constancy for captured images.

Many auto white balance algorithms follow a two-stage process:

Illumination estimation: this can be done explicitly by choosing from a known set of possible illuminations or implicitly with assumptions about the effect of such illuminations. The algorithms implemented in librraew use implicit estimation.
Image color correction: this is achieved through an independent gain adjustment of the three color signals. Commonly only the blue and red gains are adjusted assuming the red gain is fixed.

Auto exposure

One of the main problems affecting image quality, leading to disappointing pictures, comes from improper light exposure. The image exposure is the amount of light that reaches the sensor. Exposure determines the lightness or darkness of the resulting image. If too much light strikes the image sensor, the image will be overexposed, washed out, and faded. If too little light reaches the camera sensor produces an underexposed image, dark and lacking in details especially in shadow areas. Auto exposure (AE) algorithms adjust the captured image in an attempt to reproduce the most important regions (according to contextual or perceptive criteria) with an average level of brightness, more or less in the middle of the possible range.

Auto exposure algorithms involves three processes:

Light metering: this is generally accomplished using the camera sensor itself or an external device as exposure detector.
Scene analysis: brightness metering methods use an estimation of the scene illumination according to image metrics. Using the oerall illumination value, brightness adjustments can be calculated to produce the best exposure.
Image brightness correction: this ensures that the correct amount of light reaches the image sensor by adjusting the illumination and shutter time parameters. The image sensor parameter is often called the exposure time. The exposure time is defined as the amount of time that the sensor integrates light. In other words, it determines how long the sensor photo diodes array is exposed to light.

Documentation

Librraew 1.1 (current version)
Librraew 1.0

Using the demo version of librraew

You can request a demo version of librraew in order to test the auto-white balance and auto-exposure algorithms to see if the technology meets your needs. This library will allow you to use all the features that comes with the full version of the librraew but with the following limitations:

The algorithm will darken the image periodically.
After awhile the algorithm will stop working and the image capturing will be done with the last values calculated by the library. In order to test the library again you will need to restart the algorithm.

Go to download center

Go to RidgeRun Store

References

Battiato, G. Messina, and A. Castorina. Exposure correction for imaging devices: an overview. In Single-Sensor Imaging: Methods and Applications for Digital Cameras, chapter 12. Rastislav Lukac, October 2008.
Lee J.S., Jung Y.Y, Kim B.S., and Ko S.J. An advanced video camera system with robust af, ae, and awb control. IEEE Transactions on Consumer Electronics, 47:694–699, August 2001
Edmund Y. Lam. Combining gray world and retinex theory for automatic white balance in digital photography. Consumer Electronics, 2005. (ISCE 2005). Proceedings of the Ninth International Symposium on, pages 134–139, June 2005.
Edmund Y. Lam and George S. K. Fung. Automatic white balancing in digital photography. In Single-Sensor Imaging: Methods and Applications for Digital Cameras. Taylor & Francis Group, LLC, 2009.
Nitin Sampat, Shyam Venkataraman, Thomas Yeh, and Robert L. Kremens. System implications of implementing auto-exposure on consumer digital cameras. Proc. SPIE. Sensors, Cameras, and Applications for Digital Photography, 3650:100–107, March 1999

@@ Line 1: / Line 1: @@
 = Introduction =
-Video capture quality can be enhance with image processing, like auto white balance(AWB) and auto exposure algorithms(AE):
-*Auto exposure performs automatic adjustments of the image brightness according to the amount of light that reaches the camera sensor.
-*Auto white balance automatically compensates color differences based on lighting so white actually appears white.
-Some camera sensors don't include auto white balance and/or auto exposure processing, so RidgeRun offers a library with AE and AWB algorithms for the Leopard Board DM365 and the 5Mpixel camera.
+The DM365 and DM368 support the H3A hardware accelerator for supporting auto white balance (AWB) and auto exposure (AE).  CMOS or CCD sensor video capture quality can be enhanced with AWB and AE image processing:
-= Design =
+* Auto exposure performs automatic adjustments of the image brightness according to the amount of light that reaches the camera sensor.
-Three applications are required to support the auto exposure and auto white-balance (AEW) adjustments:
+* Auto white balance automatically compensates color differences based on lighting so white actually appears white.
-*Ipiped, a D-Bus server for controlling and configuring the camera sensor, the dm365 video processor and the aew library.
-*Librraew, a library that includes auto white balance and auto exposure algorithms.
-*Ipipe-client, an D-Bus client that can be used to invoke any of the methods supported by the Ipiped.
-= Running Ipiped =
+Some camera sensors don't include auto white balance and/or auto exposure processing, so RidgeRun offers a library with AE and AWB algorithms called '''librraew'''. This library was initially developed for the DM365/DM368 (DM36x) platform.  The DM36x video processing front end (VPFE) has an H3A engine designed to support control loops for auto focus, auto white balance and auto exposure by collecting statistics about the imaging/video data. There are two blocks in this module:
-Ipiped must run in background:
-<pre>
- ipiped &
-</pre>
-Ipiped registers with D-Bus and waits until ipipe-client requests to execute a method.
+* Auto focus engine
+* Auto exposure and auto white balance engine
-= Running Ipipe-client =
+The librraew library only uses the auto exposure and auto white balance hardware engine which requires the video frames to be in the Bayer color space. The DM36x does not allow the H3A engine to be used when the color space is YCbCr, which is common if you are using NTSC/PAL composite video input.
-Ipipe-client is a Dbus client that use commands to invoke methods of the ipiped, so ipiped must be running to use ipipe-client. A command can required arguments depending of the functionality. Ipipe-client has two operation modes, you can ask to execute a single command or you can open an interactive console to execute a group of commands.
-To execute a single command, you can use the following command line syntax
+The H3A engine divides the frames into two dimensional blocks of pixels referred as windows. The engine provides image/video metrics:
-<pre>
- ipipe-client <command> <argument 1> ... <argument n>
-</pre>
-To get into the interactive console, you have to run ipipe-client without any command. Then to execute a command you only need to use the command and the required arguments.
+* Accumulation of clipped pixels along with all non-saturated pixels in each window on a per color basis.
-<pre>
+* Accumulation of the sum of squared pixels per color.
-ipipe-client
+* Minimum and maximum pixels values in each window on a per color basis.
-ipipe-client$ <command 1> <argument 1> ... <argument n>
-ipipe-client$ <command 2> <argument 1> ... <argument n>
-</pre>
-To quit the interactive console you can use quit or exit.
-In order to know the commands that are available run:
+The DM36x H3A engine can be configured to use up to 36 horizontal windows with sum + {sum of squares or min+max} output or up to 56 horizontal windows with sum output. The H3A engine can also be configure to use up to 128 vertical windows. The width and height for the windows is programmable.
-<pre>
-ipipe-client help
-</pre>
-or get into the interactive console and execute help.
-This shows a description of each command, as follows:
+The librraew library was tested using an Aptina MT9P031 CMOS sensor.  Support for other sensors was added later, thus validating the librraew design.  If you provide the appropriate sensor-specific functions for the library, it can work with any sensor. The implementation is a plain C library and can be re-used with and integrated with any application capable of making C function calls. [https://github.com/RidgeRun/ipiped/wiki Image Pipe Daemon] uses librraew to provide auto exposure/Auto white balance.
-<pre>
+= License =
-Command                         Description
-help                    Displays the help text for all the possible commands or a specific command.
+RidgeRun auto-exposure/auto-white-balance library (C) Copyright 2010 - RidgeRun LLC.
-set-debug               Enable/Disable debug messages.
-init-aew                Initialize AEW algorithms.
-stop-aew                End AEW algorithm.
-shell                   Execute a shell command(shell_cmd) using interactive console.
-ping                    Show if ipipe-daemon is alive.
-quit                    Quit from the interactive console.
-exit                    Exit from the interactive console.
-get-video-processor     Show the video processor that is being used.
-get-sensor              Show the sensor that is being used.
-run-config-script       Execute a group of ipipe-client commands.
-set-previewer-mode      Configure previewer on continuous or one-shot mode.
-set-bayer-pattern       Sets R/Gr/Gb/B color pattern to the previewer.
-set-digital-gain        Sets red (R), green (G) and blue gains (G) on the ipipe.
-get-digital-gain        Returns the gain value for each color component(RGB).
-set-luminance           Brightness(Br) and contrast(C) adjustment.
-get-luminance           Returns the value of the Brightness(Br) and contrast(C) adjustment.
-flip-vertical           Flips the image vertically(on the sensor).
-flip-horizontal         Flips the image horizontally (on the sensor).
-set-exposure            Sets the effective shutter time  of the sensor for the light integration.
-get-exposure            Gets the exposure time of the sensor in us.
-set-sensor-gain         Sets red(R), green(G) and blue(B) gain directly on the sensor.
-get-sensor-gain         Gets sensor red(R), green(G) and blue(B).
-</pre>
-If you want more detailed information about a command execute:
+== Evaluation and Development License ==
-<pre>
-ipipe-client help <command>
-</pre>
-= Running Librraew =
+Subject to the terms and conditions of RidgeRun's SDK license, RidgeRun hereby grants to customer a product - based, non - exclusive, non - transferable, non - sublicensable, limited, worldwide license to install and use, for internal purposes only, an unlimited number of copies of the source and object code versions.
-Auto exposure and auto white balance adjustments can be started with an ipipe-client's command called init-aew. Init-aew requires some arguments to define the algorithms and other parameters. To see the arguments required you can request for help that show you the list as follows:
+== Distribution License ==
-<pre>
+Subject to the terms and conditions of RidgeRun's SDK license, RidgeRun hereby grants to customer a non-exclusive, non-transferable, non-sublicensable, limited, worldwide license to distribute RidgeRun Software in object code format only (no source code) in one product model sold by the customer.
-Command: init-aew
-Syntax: init-aew <WB> <AE> <G> <EM> <T[us]> <fps> <seg> <width> <height>
-Description: Initialize AEW algorithms
-Arguments:
-        WB: white balance algorithm, the options are:
-                G -for gray world algorithm
-                W -for retinex algorithm
-                N -for none
-        AE: auto exposure algorithm, the options are
-                EC -for electronic centric
-                N -for none
-        G: gain type, the options are:
-                S -to use the sensor gain
-                D -to use the digital
-        EM: exposure metering method, the options are:
-                S -for spot metering that take into account the light
-                information of a small portion in the center of the
-                frame and the rest is ignored
-                P -for partial metering that take into account the
-                light information of a larger portion in the center
-                of the frame (10% - 15%) and the rest of the frame is ignored.
-                C -for center weighted metering that take into account
-                the light information coming from the entire frame with
-                emphasis placed on the center area
-                A -for average metering that take into account the light
-                information from the entire frame without weighting
-                SG -for segmented metering that divides the frame
-                on 6 pieces and weighting them to avoid backlighting
-        T: wait time in us, specifies the time between
-                algorithm adjustments, max value=1s=1000000us
-        fps: minimum frame rate
-        seg: frame segmentation factor, each frame is segmented into
-                regions, this factor represents the percentage of the
-                maximum number of possible regions
-        width: captured video/image horizontal size
-        height: captured video/image vertical size
-</pre>
+= Limitations =
-Also you can stop automatic adjustments with the command stop-aew
+There are some not-so-obvious limitations when using the H3A engine:
-Some of the init-aew arguments need to be explained in more detail:
+* AWB/AE correction limited to window sampling method listed above.
-* WB: as you see above this parameter indicates the AWB algorithm you want to use.
+* Can not use H3A engine with YCbCr color space, which includes NTSC/PAL composite video input.
-**The Gray World algorithm is based on the assumption that given an image with sufficient amount of color variation, the average reflectance of the scene is achromatic(gray). If the scene has a color that dominates, the results of the algorithm may not be satisfactory.
+* Auto exposure can affect the video frame rate with dark images.  Set a maximum exposure limit to keep the frame rate from dropping below an acceptable value.
-**The White Patch algorithm assumes that the maximum response in an image is caused by a perfect reflector, so represents the color of the illumination. This algorithm can be used on images without saturated pixels.
+* Only tested with Linux 2.6.32 and the RidgeRun MT9P031 V4L2 driver.
-* AE: indicates the AE algorithm, for the moment there is only one algorithm: Electronic centric(EC). This algorithm uses the user defined metering system to get the scene illumination and tries to approach the brightness level to the mid-tone of intensity.
-* EM: this parameter defines the brightness metering system that is going to be used for the auto exposure algorithm.
+= Algorithms =
-**S: Averages the light information of a small portion in the center of the frame (1% - 5% of the entire image) the rest of the frame is ignored. This system is good for scenes that have a principal object and you are only interested on it, you don't care the background, even more on very high contrast scenes
-**P: Average the light information of a larger portion in the center of the frame (10% - 15% of the entire image) the rest of the frame is ignored. It is generally used when very bright or very dark areas on the edges of the frame would otherwise influence on a bad way the scene illumination.
+== Auto white balance ==
-**C: Average the light information coming from the entire frame with emphasis placed on the center area. This algorithm can be used when you want that the whole scene be well illuminated and not be affected for the small edges brightness variations. The subjects of the picture must be at the center of the image. But, if a backlight is present into the scene the central part results darker than the rest of the scene and unpleasant underexposed foreground is produced.
-**A: Average the light information coming from the entire frame without weighting any particular portion of the metered area. This algorithm can be used on scenes that not have a principal object and you want an average illumination. If the scene has a high contrast, the algorithm cause under or over exposure of parts of the scene.
+When an image of a scene is captured by a digital camera sensor, the sensor response at each pixel depends on the scene illumination. Depending of the illumination, a distinct color cast appears over the captured scene. This effect appears in the captured image due to the color temperature of the light. If a white object is illuminated with a low color temperature light source, the object in the captured image will have a reddish tint. Similarly, when the white object is illuminated with a high color temperature light source, the object in the captured image will appear somewhat blue instead of pure white. The human eye compensates for color cast automatically through a characteristic known as color constancy, allowing the colors to be independent of the illumination. Auto white balance tries to simulate the color constancy for captured images.
-** SG: This algorithm is designed for scenes that have a principal object in backlighting condition. Emphasize the luminance of the main object according to the degree of backlighting. Divides the frame on 6 pieces and weighting them.
-*T: the time between interactions defines how fast the algorithm can adjust the scene parameters. If you don't need fast changes you can use a greater time to get less CPU usage.
+Many auto white balance algorithms follow a two-stage process:
-*seg: this factor is related with the amount of CPU usage and the auto-adjustments precision. If you use a high segmentation percentage you will have greater CPU usage but you will get more precision on the adjustments.
+* Illumination estimation: this can be done explicitly by choosing from a known set of possible illuminations or implicitly with assumptions about the effect of such illuminations. The algorithms implemented in librraew use implicit estimation.
+* Image color correction: this is achieved through an independent gain adjustment of the three color signals. Commonly only the blue and red gains are adjusted assuming the red gain is fixed.
+== Auto exposure ==
+One of the main problems affecting image quality, leading to disappointing pictures, comes from improper light exposure. The image exposure is the amount of light that reaches the sensor. Exposure determines the lightness or darkness of the resulting image. If too much light strikes the image sensor, the image will be overexposed, washed out, and faded. If too little light reaches the camera sensor produces an underexposed image, dark and lacking in details especially in shadow areas. Auto exposure (AE) algorithms adjust the captured image in an attempt to reproduce the most important regions (according to contextual or perceptive criteria) with an average level of brightness, more or less in the middle of the possible range.
+Auto exposure algorithms involves three processes:
+* Light metering: this is generally accomplished using the camera sensor itself or an external device as exposure detector.
+* Scene analysis: brightness metering methods use an estimation of the scene illumination according to image metrics. Using the oerall illumination value, brightness adjustments can be calculated to produce the best exposure.
+* Image brightness correction: this ensures that the correct amount of light reaches the image sensor by adjusting the illumination and shutter time parameters. The image sensor parameter is often called the exposure time. The exposure time is defined as the amount of time that the sensor integrates light. In other words, it determines how long the sensor photo diodes array is exposed to light.
+= Documentation =
+* [[Librraew 1.1]] (current version)
+* [[Librraew 1.0]]
+= Using the demo version of librraew  =
+You can request a demo version of librraew in order to test the auto-white balance and auto-exposure algorithms to see if the technology meets your needs. This library will allow you to use all the features that comes with the full version of the librraew but with the following limitations:
+*The algorithm will darken the image periodically.
+*After awhile the algorithm will stop working and the image capturing will be done with the last values calculated by the library. In order to test the library again you will need to restart the algorithm.
+[https://ridgerun.com/downloadcenter.shtml Go to download center]
+[https://ridgerun.com/store/ Go to RidgeRun Store]
+<div id="-chrome-auto-translate-plugin-dialog" style="opacity: 1 !important; background-image: initial !important; background-attachment: initial !important; background-origin: initial !important; background-clip: initial !important; background-color: transparent !important; padding-top: 0px !important; padding-right: 0px !important; padding-bottom: 0px !important; padding-left: 0px !important; margin-top: 0px !important; margin-right: 0px !important; margin-bottom: 0px !important; margin-left: 0px !important; position: absolute !important; top: 0px; left: 0px; overflow-x: visible !important; overflow-y: visible !important; z-index: 999999 !important; text-align: left !important; display: none; background-position: initial initial !important; background-repeat: initial initial !important; "><div style="max-width: 300px !important;color: #fafafa !important;opacity: 0.8 !important;border-color: #000000 !important;border-width: 0px !important;-webkit-border-radius: 10px !important;background-color: #363636 !important;font-size: 16px !important;padding: 8px !important;overflow: visible !important;background-image: -webkit-gradient(linear, left top, right bottom, color-stop(0%, #000), color-stop(50%, #363636), color-stop(100%, #000));z-index: 999999 !important;text-align: left  !important;"><div class="translate"></div><div class="additional"></div></div>[[Image:]]</div>
+= References =
+# Battiato, G. Messina, and A. Castorina. Exposure correction for imaging devices: an overview. In Single-Sensor Imaging: Methods and Applications for Digital Cameras, chapter 12. Rastislav Lukac, October 2008.
+# Lee J.S., Jung Y.Y, Kim B.S., and Ko S.J. An advanced video camera system with robust af, ae, and awb control. IEEE Transactions on Consumer Electronics, 47:694–699, August 2001
+# Edmund Y. Lam. Combining gray world and retinex theory for automatic white balance in digital photography. Consumer Electronics, 2005. (ISCE 2005). Proceedings of the Ninth International Symposium on, pages 134–139, June 2005.
+# Edmund Y. Lam and George S. K. Fung. Automatic white balancing in digital photography. In Single-Sensor Imaging: Methods and Applications for Digital Cameras. Taylor & Francis Group, LLC, 2009.
+# Nitin Sampat, Shyam Venkataraman, Thomas Yeh, and Robert L. Kremens. System implications of implementing auto-exposure on consumer digital cameras. Proc. SPIE. Sensors, Cameras, and Applications for Digital Photography, 3650:100–107, March 1999
 [[Category:Whitepaper]]