User manual MATLAB IMAGE ACQUISITION TOOLBOX 3

[. . . ] Image Acquisition ToolboxTM 3 User's Guide How to Contact The MathWorks Web Newsgroup www. mathworks. com/contact_TS. html Technical Support www. mathworks. com comp. soft-sys. matlab suggest@mathworks. com bugs@mathworks. com doc@mathworks. com service@mathworks. com info@mathworks. com Product enhancement suggestions Bug reports Documentation error reports Order status, license renewals, passcodes Sales, pricing, and general information 508-647-7000 (Phone) 508-647-7001 (Fax) The MathWorks, Inc. 3 Apple Hill Drive Natick, MA 01760-2098 For contact information about worldwide offices, see the MathWorks Web site. Image Acquisition ToolboxTM User's Guide © COPYRIGHT 2003­2010 by The MathWorks, Inc. The software described in this document is furnished under a license agreement. The software may be used or copied only under the terms of the license agreement. [. . . ] You can use the AVI file object returned by the avifile function, aviobj, to modify characteristics of the AVI file by setting the values of the object's properties. For example, you can specify the codec used for data compression or specify the desired quality of the output. 5-46 Logging Image Data to Disk For more information about AVI file objects, see the MATLAB avifile documentation. For more information about using AVI files to log image data, see the following topics. · "Logging Grayscale Images" on page 5-47 · "Guidelines for Using an AVI File Object to Log Image Data" on page 5-47 · "Closing the DiskLogger AVI file" on page 5-48 Logging Grayscale Images When logging images in grayscale format, such as RS170, you must set the value of the AVI object's Colormap property to be a grayscale colormap. Otherwise, the image data in the AVI file will not display correctly. This example uses the MATLAB gray function to create a grayscale colormap and sets the value of the AVI file object's Colormap property with this colormap. logfile = avifile('my_datalog. avi', 'Colormap', gray(256)); Guidelines for Using an AVI File Object to Log Image Data When you specify the AVI file object as the value of the DiskLogger property, you are creating a copy of the AVI file object. Do not access the AVI file object using the original variable name, aviobj, while the video input object is using the file for data logging. To avoid file access conflicts, keep in mind these guidelines when using an AVI file for data logging: · Do not close an AVI file object while it is being used for data logging. · Do not use the AVI file addframe function to add frames to the AVI file object while it is being used for data logging. · Do not change the values of any AVI file object properties while it is being used for data logging. 5-47 5 Acquiring Image Data Note AVI files are limited to a bit-depth of 8 bits per pixel for each band. If you have higher bit data, you should not log it to an AVI file since the AVI format is restricted to 8-bit data. If you do log higher bit data to an AVI file, it will be scaled and then logged as 8-bit data. Closing the DiskLogger AVI file When data logging has ended, close the AVI file to make it accessible outside the MATLAB environment. Use the value of the video input object DiskLogger property to reference the AVI file, rather than the variable returned when you created the AVI file object (aviobj). See "Example: Logging Data to Disk" on page 5-48 for an example. Before you close the file, make sure that the video input object has finished logging frames to disk. Because logging to disk takes more time than logging to memory, the completion of disk logging can lag behind the completion of memory logging. To determine when logging to disk is complete, check the value of the DiskLoggerFrameCount property; this property tells how many frames have been logged to disk. Note When you log frames to disk, the video input object queues the frames for writing but the operating system might not perform the write operation immediately. Closing an AVI file causes the data to be written to the disk. Example: Logging Data to Disk This example illustrates how to configure a video input object to log data to a disk file: 1 Create a MATLAB AVI file object -- Create the MATLAB AVI file that you want to use for data logging, using the avifile function. You specify the name of the AVI file when you create it. my_log = 'my_datalog. avi'; aviobj = avifile(my_log); aviobj 5-48 Logging Image Data to Disk Adjustable parameters: Fps: 15. 0000 Compression: 'Indeo3' Quality: 75 KeyFramePerSec: 2. 1429 VideoName: 'my_datalog. avi' Automatically updated parameters: Filename: 'my_datalog. avi' TotalFrames: 0 Width: 0 Height: 0 Length: 0 ImageType: 'Unknown' CurrentState: 'Open' 2 Configure properties of the AVI file object -- You can optionally configure the properties of the AVI file object. The AVI file object supports properties that control the data compression used, image quality, and other characteristics of the file. The example sets the quality property to a midlevel value. [. . . ] Frame rate is determined by the video format specified (standard format or from a camera file). Some devices even list frame rate as a device-specific source property. Frame rate is not related to the Block sample time option in the dialog. Block sample time defines the rate at which the block executes during simulation time. [. . . ]