The 4MEG VIDEO Model 12 was originally designed to capture, process, and display image data to a maximum depth of 8 bits (256 grey levels). Fortunately, for those interested in capturing greater pixel depths, EPIX engineers have extended this versatile 8 bit design to capture from 9 to 16 bits!
Four Key Features
There are four keys that combine to unlock the Model 12's extended pixel depth capabilities. The first key is the addition of enough RS422 receivers to accommodate all of the incoming digital video signals. The second key is the ability to drive the interface card and Model 12 with twice the camera's pixel clock frequency to capture two 8 bit words in the time required for the camera to provide one 16 bit pixel. The third key is the introduction of a 2 to 1 multiplexer to convert a 16 bit pixel into two 8 bit words. The fourth, and final key, is the ability of the Model 12's 8 bit image memory to be configured to accept video data in virtually any array shape or size - in this instance, storing a pixel as two adjacent 8 bit words. (Note: The following discussions assume use of a 16 bit digital output camera. The capture method for pixel depths of 9, 10, 11, 12, 13, 14, and 15 bits is essentially the same as for 16 bits - a single pixel of 9 to 16 bits is captured as two 8 bit words and occupies 16 bits [2 bytes] in image memory.)
Additional RS-422 Receivers
The camera outputs a 16 bit pixel as sixteen RS-422 differential signals in parallel. Sixteen RS-422 receivers are installed on the interface card. The sixteen receivers convert the RS-422 signals into
single-ended TTL level signals.
Fast Pixel Clock Rate
The imaging system uses two pixel clock frequencies based on the camera's pixel clock. The camera's pixel clock generates the fundamental frequency that drives the camera, and which is also used by the interface card to generate a second harmonic. The second harmonic drives the interface card and 4MEG VIDEO. This scheme insures accurate sampling by the 2 to 1 multiplexer and provides exact pixel registration in image memory. 16 bit cameras with pixel clock rates as fast as 25 MHz can be interfaced to the Model 12.
2 To 1 Multiplexor
TTL level signals from the RS-422 receivers are sampled by a 2 to 1 multiplexer. The multiplexer samples the TTL level signals as two 8 bit words by using the camera's doubled pixel clock frequency. The two 8 bit words are transferred (sequentially) to the Model 12 and stored in adjacent locations in image memory. The multiplexer is usually configured to sample the most significant 8 bits followed by the least significant 8 bits - other configurations, to accommodate various cameras, are possible.
Wide Image Buffers
From a hardware standpoint, the 4MEG VIDEO Model 12 operates within standard parameters to capture 16 bit resolution. Flexible buffer definition, an inherent design attribute of the 4MEG VIDEO, doesn't care how many bytes are in a pixel, or how many pixels are in a line - just as long as the total number of bytes per line is 8,000 or less (if more than 8,000 bytes per line are needed a modification can allow capture of up to 31,000 bytes per line).
EPIX provides interfaces for digital cameras from several manufacturers. Contact EPIX for a Camera Compatibility Guide. When ordering an interface, the customer is instructed to designate the pixel depth required (consult the camera manufacturer with any questions). EPIX technicians will customize the interface card to supply the requested depth. It's important to realize that camera design is a limiting factor, and the customer is cautioned against ordering an interface with a pixel depth greater than the camera manufacturer's specifications. Such an interface will not capture additional data.
9 To 15 Bit Capture vs. 16 Bit Capture
There are NO 16 bit cameras available today. The 16 bit example was used for sake of simplicity. The 8 bit digital camera remains the most popular. The 12 bit camera is becoming more common. Capture from a12 bit camera (or any digital camera that provides 9 to 15 bits) uses the same principles as capturing from a 16 bit camera. Unused data lines are grounded to minimize noise.
Status Of Software Development
The 4MEG VIDEO Model 12, with greater pixel depth, is a hardware solution currently with minimal (capture and save only) EPIX software support. EPIX technicians have verified the capture of 16 bits, but then moved to other priorities (such as support for the EPIX COC40 processor board). Sixteen bit software will be available next year. In the interim, the customer may develop custom software or use solutions from third party developers. At least two software packages, compatible with the 4MEG VIDEO Model 12, are capable of 16 bit processing: the Eye Image Calculator and Image Pro Plus for Windows. Use of Image Pro Plus for Windows currently requires saving the 16 bit image to disk prior to processing. Once Media Cybernetics finalizes the 16 bit driver specification, an integral driver will be developed.
Status On Display Plans
Since the human eye has difficulty distinguishing more than 64 levels of grey, EPIX has no plans to display more than the 256 grey levels already provided by the 4MEG VIDEO.
The history of EPIX imaging is a history of continually evolving hardware and software products that emerge with capabilities originally unintended. By designing products with a flexible architecture, conducive to modification and enhancement, applications once thought impossible are frequently realized. Sixteen bit capture is one of these. Many EPIX customers develop custom hardware and software solutions with assistance from EPIX technical support. Complicated applications sometimes require shipping custom hardware to EPIX for testing, software development, and verification. EPIX engineers are always willing to discuss new imaging applications and the need for new hardware / software features. Many custom development projects are performed at additional cost, but, if the development is thought to be of significant interest to other customers, it might be performed at no charge. Feel free to communicate with EPIX. We are here to help you achieve your imaging goals.
EPIX Vision - October 1994 Newsletter