Compare

Compare (clip_filtered, clip_original, string "channels", string "logfile", bool "show_graph")

This filter compares the original clip clip_original and its filtered version clip_filtered. The filtered version will be returned with the results of the comparison. Per frame the Mean Absolute Difference, Mean Difference and Peak signal-to-noise ratio (PSNR) is given, as well as the min (minimum), avg (average) and max (maximum) PSNR up to that frame (calculated frame-wise). Starting from v2.53, the 'Overall PSNR' (calculated over all pixels in all frames) is also shown on the output clip.

The channels (default "") string is a combination of R,G,B [,A] or Y,U,V, depending on the source clips. If it is empty, it means either "YUV" when the input clips are YCbCr or "RGB" when in the input clips are RGB.

If show_graph (default false) is true then Marc's PSNR graph is also drawn on it.

If a logfile is specified, the results will be written to a file by this name and not drawn on the clip. It is much faster if you need to compare a lot of frames.

Examples:

# Displays differences on screen
Compare(clip1, clip2)
# for creating a log file:
Compare(clip1, clip2, "", "compare.log")
# will only compare chroma channels of YUY2 clips.
Compare(clip1, clip2, "UV")

The PSNR is measured in decibels. It's defined as

PSNR(I,K) = 20 * log_10 ( 255/sqrt(MSE(I,K)) )

with

MSE(I,K) = 1/M * sum_{j,k} | I(j,k) - K(j,k) |^2

and (j,k) runs over all pixels in a frame, and M is the number of pixels in a frame.

Changes:

$Date: 2008/06/16 19:42:53 $