CHAPTER 7.

MATROX PIP-1024 IMAGE PROCESSOR

1. FUNCTIONAL DESCRIPTION

Matrox Electronic Systems, Ltd., is a Canadian company specialized in digital video technology, beginning in the 70's. I remembered that they were the first company producing Video RAM, which was used by microprocessors to generate text display to replace CRT terminals, very expensive at the time.

PIP-1024 is one of Matrox's recent product which is a single board imaging sub-system for IBM PC, XT, and AT computers. It can be though of as a memory buffer containing a digital representation of an image. The image has about 1 million pixels arranged in a 1024x1024 matrix. Any portion of a 512x512 pixels subimage can be displayed on a standard video monitor. Three interfaces exist to the memory buffer: a PC-bus interface allowing CPU or DMA access; an analog input allowing an image to be grabbed from a camera; and an analog output allowing the image to be displayed on a monitor. All three interfaces can be used at the same time without restriction,

PC accesses the buffer using X-Y coordinate addressing. Both random and sequential access are supported, the later using an autoincrement circuitry which increments the X-Y registers after each access. Using this feature, the DMA unit can be used to transfer part or all of the image to or from the PC's memory. An optional interrupt is supplied on completion of the DMA transfer, allowing the CPU to continue with other work while the transfer is taking place.

PIP-1024 digitizes images in real time, 30 frames per second, from the frame grab input port. It accepts RS-170 composite video signals from an external video source, such as a camera, a video recorder, or another PIP-1024. The digitizer runs at 10 Mhz with 8 bit accuracy. A write-protect mask can be used to selectively prevent overwriting of any of the 8 bit memory planes. Protected planes can be used to store graphics, characters, or cursors.

The image is displayed by converting the digital intensity value for each pixel back into analog video signal. The 8 bit pixel intensity is passed through a color look-up table which maps the 256 possible intensity values to 256 colors or shades of grey. The 256 displayable colors are selectable from a 16.7 million color palette. A keying circuit allows the user to overlay the contents of the frame buffer with the incoming signal.

2. THE PROGRAMMING MODEL

PIP-1024 talks to the PC host through a group of I/O ports on the PC-bus. The locations and functions of these ports are summarized in Figure 13. The absolute port addresses can be changed by a jumper on the PIP-1024 board.

Figure 13. PIP-1024 Register Addresses and Functions

026C Status Control 0

066C Snapshot Control 1

0A6C Clear interrupt Control 2

0E6C Control mask data

126C CRTC status CRTC address

166C CRTC data CRTC data

1A6C Video gain

1E6C Video set up

226C Input LUT data

266C Output blue LUT data

2A6C Output green LUT data

2E6C Output red LUT data

326C X pixel address

366C Y pixel address

3A6C Pixel data Pixel data

02F4(absolute) Interrupt enable

It is not appropriate to discuss the bits and fields in all these registers in great details here. One would have to refer to the PIP manual for detailed information. To control the image processor board, the control registers 0 and 1 are used to select functions like enabling the look-up tables (LUT), enable DMA read or write, selecting input channel, internal or external sync, input keying, enabling continuous frame grabbing or snapshot, etc.

The PIP board uses a Synertek SY6845E CRT controller chip to generate all the video timing signals and to control the image buffer memory. This CRTC chip is a very complicated device, having 22 internal registers for its configuration and operation. It is accessible by the PC host through two PC I/O ports at 126C and 166C. This is the same video chip used in IBM PC for color and monochrome displays. Normally the PIP user does not have to touch this chip, as it is automatically configured by PIP board.

PIP is booted into the monochrome mode, in which the look-up tables for the red, green, and blue channels are initialized to a unity function. To display pseudo colors, one will have to rewrite the look-up tables to specify the desired color transformation. This is done by writing into the proper LUT through the corresponding LUT data register. The byte address in the LUT is selected by writing to the X-pixel register.

To read or write directly from/to the image buffer, the X and Y coordinate of the desired pixel must be written into the X- and Y-pixel address registers, and then the pixel data can be read or written through the pixel data register. Part of the Control 2 register must be used because it takes 20 bits of address to locate a pixel in a 1024x1024 pixel array. Consecutive bytes in the image buffer can be accessed when the Counter-Enable bit in Control 0 register is set. This is convenient to upload an image from PC to PIP or download an image from PIP to PC. Two other bits in Control 0 register control the direction and transferring of data to/from the PC in the DMA mode.

3. PROGRAMMING PIP-1024

Matrox supplies very extensive software for PIP-1024. It includes an interactive control program PIPINT, and several libraries to be linked with FORTRAN or C programs. When PIPINT is loaded into PC, the user can type in many image processing commands to do many things like acquiring images, enhancing the images, upload/down load images, etc. These interactively executable functions are also in the libraries, readily callable from FORTRAN or C programs. Novice users and sophisticated users can all make this board to do useful work in a relatively short time. Matrox did a very good job in supporting the hardware.

In spite of the good software tools supplied by Matrox, I still feel being put in a straight-jacket in using PIPINT. If what you wanted to do is what was programmed in PIPINT, it does a good job. But you always want to do something more sophisticated, or just plainly different. Forth gives you the freedom of tailoring the system to your own needs. The program in Listing 9 is my way of using PIP-1024 through Forth, which is more elegant, I think, than PIPINT, because it can be customized to any application.

When I started to use PIP-1024, I tried to exercise several bits in the control registers which produced visible results on the CRT monitor, to make sure that I had the full control over the system. Several of these functions are shown in Screen 1 of Listing 9. SNAP takes a snap shot and shows an image grabbed from a video camera on the monitor. After I got an image in the image buffer memory, I could then enhance the image by changing the brightness and contrast of the display using the commands GAIN and OFFSET. MASK disabled some bits in the frame grabbing process and produced very interesting effect when two images were superposed in different memory planes.

CTRL0, CTRL1, and CTRL2 are commands to deposit byte patterns into the control registers. They form the basis to build other more powerful image processing commands. They are used to define the functions in Screen 2.

VREAD and VWRITE in Screen 3 are basic words to copy image data between the PIP image buffer and PC memory. They invoke the command VRAM to set up PIP for autoincrement memory access, so that every time PIP memory is accessed, the X,Y address registers are incremented, making the next byte in image buffer accessible in the next memory cycle.

In one of our applications, we wanted to transfer subimages of 128x128 pixels between PIP and the disk on PC. It required that a subimage anywhere in the image buffer could be accessed. (LINE) in Screen Screen 4 initializes the address registers to access one line of image data at the x,y coordinates. ROWR reads 128 bytes from image buffer to PC and ROWW writes 128 bytes from PC to image buffer. STORE-IMAGE picks a subimage at (x,y) and stores it in the currently opened file. FETCH-IMAGE gets the data from the current file to a subimage in PIP.

Pseudo color is always fun. Any grey scale image can be made more interesting by coloring different parts with different colors. The commands RED, GREEN, and BLUE write LUT look-up tables to the corresponding channels, assuming that the address of a 256 byte table is on the stack. COLOR-MAP creates a triangle function in the buffer SCRATCH. By fetching different regions in the SCRATCH buffer into the red, green, and blue LUT's, we can create interesting pseudo color schemes. One of such scheme is realized in the command PSEUDO-COLOR in Screen 7, which produces a color sequence of black-red-green-blue-black with increasing pixel values. NORMAL displays a normal black/ white image. REVERSE turns black to white and white to black.

ENHANCE is an interesting way to enhance a black/white image. It takes two parameters on the stack: a contrast value and a brightness value. It produces a look-up table with an S- shaped intensity transformation curves: the center of the sloped portion of the curve is specified by brightness value and the slope of this portion by the contrast value. Figure 14 shows the intensity transformation curves produced by the commands

1 128 ENHANCE and 3 75 ENHANCE

The latter command enhances the pixel values between 75-42 and 75+42, the pixels with values from 0 to 42 are displayed in black, and those between 117 and 255 are displayed in white. ENHANCE is very effective in sharpening a poor image in which pixel values are compressed into a narrow band, such as an image taken by a camera with insufficient lighting.

Figure 14. Intensity Transformation Curves.

. . . . . . . . . . . . . . . . . . . .

. + . +++++++++++++

. + . . + .

Output. + . Output. + .

Value . + . Value . + .

. + . . + .

+ . . . . . . . . . +++++++ . . . . . . .

Input Value Input Value

1 128 ENHANCE 3 75 ENHANCE

Listing 9. Matrox PIP-1024 utility

Figure 15. Matrox PIP-512 brochure