<P> The only pixels that should change are the ones that are the same color as the field, typically several shades of green . As a result, there are a few situations that are difficult . One is when the player's uniform color nearly matches that of the field (for example, the Green Bay Packers' jersey on a bright, sunny day, or for Boise, Idaho's Bronco Stadium, where the field and the home team uniform share the same blue shade). The other is when the field itself changes, like during a rain / snow storm or if the grass field becomes very muddy . In those cases, the field's color palette would need to include brown and / or white shades . The most difficult situations are when the shade of the field is constantly changing as in situations where moving clouds are shadowing the field on some spots, but not others, but continue to move across the field . </P> <P> The data collection and computation also requires time . The audio feed goes to an audio delay to be synchronized with the delayed video . The total delay for the viewer from the live feed ends up being about 2 / 3 of a second . </P> <P> After the camera computer has determined which pixels represent the 1st & Ten line, it takes that pixel information and draws the yellow line in video format at around 60 times per second (depends on video refresh frequency). A 2011 study conducted by SportVision determined the yellow line has an average margin of error of 1.38 inches compared to the official first down marker . </P> <P> In recent years the system has been upgraded to add more features . During Fox broadcasts, the Sportvision system also generates an arrow - like graphic on the field with down and distance text information inside of an arrow pointing in the direction of play . Competitors have also added this feature in recent years . </P>

What do the blue and yellow lines mean in football