Rate, Height & Mode

For those who have used film based systems in the past, frame rate should be thought of as the equivalent of “film speed”. There are two factors to be considered when setting the frame rate of the EtherLynx camera:

• Higher speeds are used for faster events. When timing an open-wheel car race, it is normal to use a higher rate than for a 10,000m running event. The reason is simply that faster objects need to have their picture taken more often in order to keep a discernible distance between them in the picture. As a point of reference, a world class 100m could be taken at 2000 frames per second and the resulting picture would have about as much space separating the finishers as there was in real life. If the picture was taken at 5,000 frames per second, the people would appear “fat” in the image, but there would also be more space in between the participants, therefore making it easier to pick a close race.

• Higher speeds require more light. If the electronic sensor is given less time to “expose” by taking faster images, the picture is going to be darker. Fortunately, we can compensate for this by artificially boosting the signal.

Setting the frame rate is simply a matter of clicking on the box that contains the frame rate in the Hardware Control window, Event window or Camera Settings dialog, typing in a new value over the old one and hitting the Enter key.

Frame height refers to the number of pixels of the image that are transmitted to the computer by the camera.

If you are relying on being able to read hip numbers as your means of identifying the competitors in an event, then you will need to ensure that you have the height set to a high enough number to make the numbers clear. The downside to having the height set at a high number is that the file size will be bigger, and, as a result, when events are saved they will take up more disk space.

A good rule of thumb for sprint races in track and field is to use a rate which is at least 1.5 times the height setting (i.e., a rate of 1000 and height of 640). For events that have particularly wide fields of view, such as horse tracks, this ratio might be as low as 1:1 (i.e., a rate of 2000 and height of 2048). Other events with small fields of view, such as dog racing, might use a ratio as high as 4:1 (i.e., a rate of 4000 and height of 1024).

The settings for Mode (Pixel Mode) control the size of light-sensitive cell clusters that the computer uses to take information from the camera and display in a single pixel on the screen.  The effect of changing this setting is to alter the height dimension of the image on the screen. A lower value of mode, will show a smaller resolution, and vice-versa.

For example, changing the Pixel Mode setting from Zoom 100% to Zoom 200% (while keeping the same Height setting) is to accomplish a virtual zoom in (see Digital Zoom Feature for details).

There are multiple options for Pixel Mode, depending on the EtherLynx camera model:

• Zoom 300%. (Worst signal-to-noise ratio, greatest virtual zoom-in effect.)
• Zoom 200%.
• Zoom 150%.
• Zoom 100%.
• Wide 50%.
• Wide 33%.
• Wide 25%. (Best signal-to-noise ratio, greatest virtual zoom-out effect.)

The allowable range for the Frame Height is dependent on the selected Pixel Mode. To take full resolution images that show the widest view of the finish line, the Frame Height should always be adjusted to the max allowable value.

At Zoom 100%, the maximum Height represents the number of pixels on the EtherLynx camera sensor. Using the EtherLynx Vision PRO as an example, Zoom 100% offers a maximum Frame Height of 1024 pixels. The max for Zoom 200% is 2x the number of pixels (2048). For Wide 50%, it is half (512). You may very well guess that the max at Wide 25% is... 256.

Knowing this, you may wonder what is the difference between a Zoom 200%/2048 pixel image and a Wide 25%/256 pixel image? Can you see more of the finish line (more content) with one than the other? The answer is no. They both show exactly the same view of the finish line. However, the Zoom 200%/2048 pixel settings will produce images that have 64 times the resolution of the other, because both the number of pixels and rate will be multiplied by a factor of 8.

And how is the Frame Rate impacted. To maintain the same ratio of horizontal and vertical image, the Frame Rate should be adjusted by the same factor as the Frame Height. For example, if 1000fps by 1024 pixels @ Zoom 100% renders correct proportions (a wheel is round, not oval) than change to Zoom 200% and 2048 pixels requires 2000fps to maintain the same ratio. Just as well, 500fps are required to take the same image in Wide 50%.

Useful Scenarios

• In Rowing and Paddle Sports, the finish line is wide and the object is moving relatively slowly (compared to Cycling, for example). Capturing images at 1000 fps in Zoom 100% may have objects look stretched out. With the Digital Zoom option, the operator can double the vertical resolution using Zoom 200% and reduce the stretched out effect.
• In Cycling, fast finishes in low light conditions may force the operator to decrease the Frame Rate to reduce the gain and noise level. Doing this may cause the objects to appear too thin. By changing to Wide 50%, it is possible keep the same ratio and halve the Frame Rate.
• In Speed Skating, you may want to print the photo-finish image. Using Wide 25%, you notice the image is very small or very pixellated if zoomed in. By using the Digital Zoom options of Zoom 200% (8x the image height) and matching the Frame Rate (8x), the image resolution is increased by a factor of 64!

Learn more about Gain Control Tools.