EPIX is pleased to announce that the pixel clock range for the 4MEG VIDEO Model 12 has been extended. Previously, pixel clock frequencies between 2 MHz and 45 MHz were supported. The Model 12 can now be configured to use pixel clocks down to 32 KHz or up to 50 MHz!
The major constraint to extending the 4MEG VIDEO's pixel clock range is image memory. A second constraint is imposed by the 4MEG VIDEO's on-board pixel clock modules (which aren't available below 2 MHz or above 50 MHz). The introduction of faster memory chips has allowed the Model 12 to reach the maximum frequency of its on-board pixel clock modules. Use of memory chips with lower refresh cycle requirements, and use of techniques to circumvent the 2 MHz lower limit, allow image capture down to the 32 KHz pixel clock frequency.
Slow scan memory boards, which allow capture down to 32 KHz, are available with either 4 or 16 megabytes of image memory.
The 50 MHz pixel clock frequency has been achieved by using 40 nanosecond access time drams on the 4 megabyte image memory board. Faster memory is not currently available for 16 or 64 megabyte image memory boards.
Pixel Clock Rates Go Down to 32 KHz
A 4MEG VIDEO Model 12, ordered with a new slow scan image memory board, is able to accept pixel clock frequencies as slow as 32 KHz! This slow scan option allows longer integration times for cameras and improves resolution for scanning electron microscope and sonar applications. There are two options for sampling below 2 MHz:
Use on External Pixel Clock.
If an external pixel clock is available, it can be easily interfaced to the Model 12. Selection of the external pixel clock is accomplished through software. An external pixel clock signal can be input through either the DB25 I/O connector or through the V-8 connector.
Use Subsampling and 32K HCM Option.
What is Subsampling? In most imaging applications a pixel is captured with each pulse of the pixel clock (except during blanking). Subsampling is the process of capturing pixels at a rate slower than the base pixel clock frequency. For example, 1 pixel can be captured for every 2 pulses of the pixel clock providing an effective sampling rate ½ the base pixel clock frequency. The use of subsampling allows a higher frequency pixel clock rate to clock lower-frequency sampling. 4MIP software provides this option.
What is the 32K HCB Option, and why use it?
The Model 12, in standard configuration, can generate up to 8000 pixel clock pulses for each uninterrupted period of image capture (8000 pulses for each horizontal line of video) capturing up to 8000 pixels per line. A horizontal sync signal is required after pulse 8000, which generates horizontal blanking - a period when pixels can't be captured.
The 32K Horizontal Control Memory (HCM) extends the length of an uninterrupted period of image capture to 31,000 pixel clock pulses before blanking is required. Using a 2 MHz pixel clock, pixel sampling width of 62, and a horizontal line time of 15.5 milliseconds, allows capture of 500 pixels per line at an effective sampling rate of 32 KHz. The sampling period for a pixel captured in this format is 31 microseconds - this is 370 times longer than RS-170's 84 nanoseconds per pixel. (The sampling period for a single pixel captured in RS-170 format [752 pixels, 14.3 MHz, 63.5 microseconds per line] is 84 nanoseconds.)
Pixel Clock Rates Up to 50 MHz!
High resolution capture and display is now available at up to 50 MHz - better than 1KxlK resolution! Using RS-343 timing, a 1304x974 frame (4x3 aspect ratio) can be captured and displayed at 30 frames per second! This high resolution capability is useful in medical imaging applications (CT and MRI) and for use with high resolution cameras. EPIX will make announcements in EPIX Vision as high resolution cameras are tested and verified compatible with this higher pixel clock capability.
EPIX Vision - January 1994 Newsletter