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The analog line overlay level ("Interpolator")
blog by omitting every third row, the contribution of these lines would be lost to the converted television picture. This brings two problems. The first is the omitted line after each screen change to another, resulting in a through-going artifact in the image. Secondly, round objects 'edges'.
The term 'interpolation' is from digital converters, the expected out after the implementation of such errors. This will be presented at the line frequency analog converters not done. Since the result is similar but, I still use the familiar concept of interpolation at this point.
The attempt at least to address the first problem was, at the suggestion of Peter, reset in the so-called frame. This ensures that always the same line is omitted. So at least the very obvious passing is eliminated, but the frame reset not compatible with any vertical deflection and was therefore made the MK1 Converter disabled.
Later came to me then the idea for the row storage level, which is preparing to convert the video signal so that after the conversion is a perfect video signal is available which does not require more interpolation. This requires a special switching and overlapping procedures. In MK1 Converter
was the row storage level for experiments carried out and then switched to perfection. The following models will be used permanently, the switchable frame is reset thus become superfluous.
The following figure shows how these lines overlap stage works:
to explain it does turn out three consecutive 64μs lines, they are left in the picture red, green and brown each other drawn. If you were a line, such as the red line drawn omit, (X) are available in the converted image that is supposed to represent the contents of two rows of three lines, only the information from the green and the brown line. This leads to the above described artifacts. With a bucket brigade (CCD delay) the video signal by exactly one line length is delayed. So you have to store the desired option, the delayed and not delayed video signal after. The superposition in the drawn third money, you get a (64μs lines) video signal in which the contents of the previous line is always, as in the picture drawn in the middle, included in the current row. Can fail to properly prepared for this image signal to convert every third line and extend the remaining lines accordingly (64μs to 96μs line length), then relate these two converted lines 96μs their content from the three 64μs lines. See right. Shall bear all the rows in the 64μs-96μs line image to the new-line image. It is thus subject to any subsequent calculation 'of lost content', ie Zeileninterpolation more how it is performed in the digital process.
The picture shows a PYE LV20 1949 with test pattern on the MK II Converter. On the bright surface can be seen in the middle of the ion spot, which has burned over the years into the phosphor.
In the practice of a resistor is used to overlay. It is the resistance, which leads the undelayed video signal, at the right moment, a resistor with a Switching transistor connected in parallel.
Thus, between the 1 / 3 overlay transistor closes and opens the 2 / 3 overlay transistor to switch. When I MK Converter is an NPN transistor, in the following discussion to MK IV, a PNP transistor.
Q13 is the MK II Converter interpolator switching transistor. It turns the 680Ω resistor in parallel with the 2KΩ resistance. The delay line is about 1KΩ.
In the next blog of the MK II converter is described.
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