Evaluation of Brightness Resolution of WEFAX Images Transmitted through GMS

Abstract

The original images of Weather Facsimile, transmitted through GMS, have 64-leveled gradation. The envelope of the 2.4kHz subcarrier signal in the transmitted wave is proportional to the brightness of the image. The signal is converted to digital data with a sampling frequency of 37.8kHz. The image of 855 pixels/line, half of the original, is obtained by deducing the peak values of subcarrier oscillations and interpolating the middle points. The distribution of the number of pixels of each brightness should have 64 discrete peaks, if the image is transmitted properly. Although the distribution has discrete peaks in the low brightness region, it is rather continuous in the higher region. It seems that the 64-leveled gradation does not remain perfectly in the transmitted image. It is found out, however, that the each grade is separated spatially fairly well at the gently sloping regions in the pseudo-colored image.