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We give this as 770 ± 24 pixels, which overestimates somewhat. The feature (left hand side of window frame) is blurred over the range 746 andħ94 pixels. The image gets blurred as seen in the screenshot above. Uncertainty for the pixel measurement will increase as the train gets faster ![]() How certain are we that theįeature is exactly located at the given pixel. Give an uncertainty for the pixel measurement. #Avidemux change frame rate movieThe time measurement for our movie could be given as (value) ± 1/2 *1/30 s, or Value can be above or below the value you give as your measurement. ![]() It is common to give your measurement as (value) ± (uncertainty). Light the camera may record over most of this duration. A firstĮstimate of the uncertainty for the time measurement is 1/30 s, because it low How precise and accurate areĪ clock, the frame rates of typical phone cameras are rather accurate (they Measurements we need to consider uncertainties. We measured pixels in the plane of the exterior of the train, not in the plane of the door, because we wanted to use train windows later as reference points and the windows are in the plane of the exterior of the train.Įxample, the train moved 34 pixels, which corresponds to 54 mm or 0.054 m in 10įrames, or 0.33 s, so the speed is 0.054/0.33 m.s -1 or 0.16 m.s -1. Your camera and multiply the distance measured on the ruler by D/ d. For instance, to measure an object at distance D from yourĬamera, at right angles, you could position a ruler at distance d from Measuring the doorframe on screen with the pixel ruler gave us 764 pixels. The width of the doorframe (inside the train, for safety!) at 1.22 metres. You film a car or aeroplane, the manufacturer's website may tell you the Instance, if you filmed a basket ball, you can measure the circumference of theīall with a tape measure and that gives you the diameter of the ball. Sometimes you know the size of your object: For Ours runs at 30 fps: 1 frame in 33 ms and in our example 10 frames in Into seconds, you need to know how many frames per second (fps) your camera Ten frames the door has moved by 34 pixels. ![]() Now the feature is located at 214 pixels: The figure above is 2.733 s into the movie the screenshot below is 3.066 s Or more frames forward in the movie and measure the location of the feature again. Ruler on the screen does not matter as long as it is not moved from one pixel Set up like this, I read 248 pixels (the exact location of the Left side of the doorframe as the easily identified object (highlighted with a In the example shown below I have chosen the #Avidemux change frame rate freeRuler (We used Pascal Free Ruler) and pick a feature on your object that youĬan easily identify on the screen. And if you magnify enough, you can count pixels directly. #Avidemux change frame rate softwareUse any other software that allows you to measure pixel dimensions on theĬomputer screen. Use any other video software that allows you to move through the materialĪllows you to measure pixels on the computer screen can be found here: Video material using frame grabbing software and spreadsheet software ![]()
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