Image-capture system uses USB and LabView
A PC can capture and process images provided it's powerful enough to keep up with the data flow.
Chien-Hung Chen and Po-Jui Chen, National Applied Research Laboratories, Hsinchu, Taiwan; Edited by Martin Rowe and Fran Granville -- EDN, June 24, 2010
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Capturing and processing graphical
images requires manipulating
data into a form that you can use. This
Design Idea describes an imaging system
using a USB (Universal Serial Bus ) image-capturing system that uses OmniVision’s 640×480-pixel,
8-bit-color OV7660 image sensor. The
CY7C68013A-128AXC from Cypress
Semiconductor provides
a USB interface between a PC and
the image sensor (Figure 1). The control
software is written in LabView from
National Instruments.
To avoid losing data from the image sensor, the system employs a data buffer in the image-processing algorithm. The buffer uses system memory for data storage. The queue ensures that the system will not lose data regardless of how much time it takes to process each row in an image. This technique is useful in measurement systems in which the speed of data acquisition and data processing may differ.
Figure 2 shows the programming flow
chart. After the system starts, you must
set the driver to NI-VISA (Virtual Instrument
Software Architecture), a software
layer that provides a common programming
interface across many types of measurement
instruments and software drivers.
Once you set the driver, you can initiate
the USB device. LabView provides a
driver wizard that helps you to build drivers.
The LabView code for this graphic-system
design can easily implant USB
data transmission and its applications. Request a copy of the LabView code here.
After initializing the USB device, the software allocates system memory in a FIFO (first-in/first out) configuration to become the data buffer. A memory endpoint sets the input buffer’s size to 4 kbytes. The software then reads the image in rows and stores data from the sensor in the buffer memory. After reading the data from the buffer, the system image uses two threads to process the data.
Figure 3 shows the LabView programming
diagram for USB data transmission.
The program includes for-loop procedures
for storing the image in the buffer
memory, reading and processing image
data, and performing state checking.
The main processing algorithm obtains
and displays red, green, and blue
data of each pixel. Figure 4 shows
the test result. The element in the buffer
shows that the system processed
614,400 pixels. The actual amount will
vary based on the PC’s performance. A
powerful PC can smoothly run this program,
whereas a weak PC will cause the
data to accumulate in the buffer.
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