Method for centering and dimensioning an image on a cathode-ray tube

A display comprising

• a cathode ray tube for displaying an image thereon;
• and
• a calculation circuit connected to said cathode ray tube for horizontal centering and horizontal dimensioning the image being displayed on said screen by
• (a) measuring durations of vertical border edges of the image and iteratively modifying adjustment values for a horizontal centering of the image to obtain equal lateral vertical edges, and
• (b) measuring the durations of the vertical border edges of the image to calculate adjustment values for a horizontal dimension of the image to cause the vertical border edges to disappear;
• said calculation circuit further checking for stability of the image by
• (a0) measuring a pair of durations of at least one of the vertical and horizontal border edges of the image,
• (a1) subtracting two successive measurements to determine a variation in the durations,
• (a2) comparing the variation with a first threshold, and stopping if the first threshold is exceeded or continuing if the first threshold is not exceeded, and
• (a3) comparing the measurements with a second threshold, and stopping if the second threshold is exceeded or continuing with at least one of steps (a) and (b) if the second threshold is not exceeded.

A display comprising

• a cathode ray tube for displaying an image thereon;
• and
• a calculation circuit connected to said cathode ray tube for centering and dimensioning the image being displayed by
• (a) measuring durations of vertical border edges of the image and iteratively modifying adjustment values for a horizontal centering of the image to obtain equal lateral vertical edges,
• (b) measuring the durations of the vertical border edges of the image to calculate adjustment values for a horizontal dimension of the image to cause the vertical border edges to disappear, and
• (c) measuring durations of horizontal border edges of the image to calculate adjustment values of a vertical dimension of the image, and to calculate adjustment values of a vertical centering of the image to cause the horizontal border edges to disappear and to center the image vertically;
• said calculation circuit indicates durations of the vertical border edges of the image by variables T1HAV and T2HAV;
• and calculates the adjustment of the horizontal dimension of the image in step (b) is based upon the formula:
• HSIZE
• =
• A
• Vopti
• ⁡
• (
• T
• ′
• /
• Td
• ′
• )
• -
• H
• AMPMIN
• H
• AMPMAX
• -
• H
• AMPMIN
• ×
• HSIZE
• MAX
• wherein:
• Avopti is an optimum amplitude of a current in a horizontal deflection coil of the cathode ray tube to obtain an image of optimum width, with the amplitude being measured for a type of cathode ray tube,
• HSIZEMAX is a maximum value of the adjustment of the horizontal dimension of the image,
• HAMPMAX is a maximum variation of a current in the horizontal deflection coil to obtain a maximum horizontal deflection, this value varies as a function of a horizontal scanning frequency,
• HAMPMIN is a minimum variation of the current in the horizontal deflection coil to obtain a minimum horizontal deflection, this value varies as a function of the horizontal scanning frequency,
• T′ is a total duration of a period T of a horizontal synchronization signal, from which are subtracted a duration of a flyback pulse TFLYBACK and a duration of safety margins, and
• Td′=T (T1HAV+T2HAV+TFLYBACK), which is a duration of the image on the screen between the border edges.