Kdenlive/Manual/View Menu/RGB Parade
RGB Parade
Display a histogram of R, G and B components of the video data. This data is a 3D histogram.
The horizonal axis represents the horizonal axis in the video frame. The vertical axis is the pixel luminance from 0 to 255. The brightness of the point on the graph represents the count of the number of pixels with this luminance in this column of pixels in the video frame.
In the sample screen shot of this green screen with a shadow on it and with a right edge that reveals a white wall you can see how the scope works. The circled regions labeled 1 are on the left side representing the fact that there is are several columns of pixels that are quite bright whitish/grey. So these regions are higher up on the Y axis.
The regions labeled 2 are in the middle of the scope and the dip in the graph there shows the shadow on the screen at this point. The average luminance of the pixels in these columns is lower.
For more information see Granjow's blog on the waveform and RGB parade scopes. This blog gives some information on how to use the data provided by the RGB parade to do colour correction on video footage.
This somewhat different to the video effect RGB Parade in that with View>RGB parade the histogram is displayed in the application whereas in the RGB Parade effect the histogram is written into the video output file.