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Calculating Image Memory For PIXCI

The PIXCI® board uses the computer's memory for image memory. Accordingly, the computer must be configured with enough memory to hold the sequence of images required by the application. The amount of required memory can be calculated using a simple formula:

Number of Pixels per Image x Number of Bytes per Pixel x Seconds/Sequence x Images/Second = Bytes/Sequence

Let's look at each of these factors in greater detail:

Number of Pixels Per Image

The PIXCI® board supports a maximum NTSC resolution of 752x480 and a maximum PAL resolution of 920x580. A 752x480 resolution provides 360,960 pixels per image: a 920x580 resolution provides 533,600 pixels per image. Lower resolutions, requiring less processing time and less image memory, can also be specified.

Number of Bytes per Pixel

The number of bytes per pixel is determined by whether grey level or color images are captured. NTSC/PAL color is captured as 8 bits of luminance and 8 bits of chrominance - or 16 bits (2 bytes) per pixel. An RS-170/CCIR image is captured as 8 bits of luminance with 4 bits of unused color data - for 12 bits (1.5 bytes) per pixel.

Seconds Per Sequence

This factor is determined by the duration of the sequence/s to be recorded. Provide your best estimate. Is there a need for holding several events in image memory at the same time? Is there a need to allow a few extra seconds before or after the event to insure that all data is captured?

Images Per Second

Do maximum capture rates need to be employed, or is there an advantage to capturing fewer images per second in favor of capturing the sequence over a longer period of time?

As an example, with an NTSC camera, PIXCI® can easily capture every frame (30 Hz), every other frame (15 Hz), every third frame (10 Hz) etc., with the camera continually operating at 30 frames per second. With a PAL camera, PIXCI® can capture every frame (25 Hz), every other frame (12.5 Hz), every third frame (8.33 Hz) etc., with the camera continually operating at 25 frames per second.

It is also possible to capture sequences of individual fields in a similar manner. An NTSC camera has a field rate of 60 Hz while a PAL camera has a field rate of 50 Hz.

Calculating Image Memory Requirements; An Example:

After determining the values for each of the 4 variables, just multiply them to determine the amount of memory required:

Capture images with 320x240 resolution (76,800 Pixels/Image), in 16 bit NTSC color (2 Bytes/Pixel), for an event that lasts 9 seconds (9 Seconds/Sequence), at a rate of 10 images per second(10 Images/Second).

The amount of memory required to record this event is:76,800 Pixels/Image x 2 Bytes/Pixel x 9 Seconds/Sequence x 10 Images/Second = 13,824,000 Bytes/Sequence

One last step - which wasn't included in the formula. . . To determine the number of MEGAbytes of memory required, divide the Bytes/Sequence by 1,048,576 Bytes/Megabyte. In this example, 13.18 Megabytes/Sequence are required.

This calculation determines the amount of memory that must be available to PIXCI® in order to capture a specified event. This memory must be provided in addition to the memory required to run application programs.

Maximum Memory Size

PIXCI® can continually capture images into as much memory as the computer has available.

EPIX Vision - March 1996 Newsletter

1. Introducing..... PIXCI
2. S-Video Image Capture Improves On NTSC Quality
3. Calculating Image Memory For PIXCI
4. Image Pro Plus For Windows - Alternative Software For EPIX Imaging Boards