[FFmpeg-user] How to set histogram size?

[Pedro]

I'm trying to add a waveform histogram to a video. I'm following this 
<https://trac.ffmpeg.org/wiki/FancyFilteringExamples#waveform> example 
but I'm having trouble setting the size of the histogram, this is code 
I'm using:

*ffmpeg -y -report -i input.mp4 -vf 
"split[a][b];[a]format=gray,histogram=mode=waveform:waveform_mode=column,vflip,split[c][d];[b]pad=iw:ih+256[padded];[c]geq=g=1:b=1[red];[d]geq=r=1:b=1,crop=in_w:220:0:16[mid];[red][mid]overlay=0:16[wave];[padded][wave]overlay=0:H-h" 
output.mp4*

I've tried to play around with the *|pad|***and *|crop|***values without 
luck.
How can I set the size of histogram to 100 pixels only?

Thank you!