Continuum intensity histogram of all penumbra pixels of the studied area. Left panel: histogram of the continuum intensity for pixels whose Stokes V profiles show only an extra blue (thin-black) or red (thin-gray) hump. Right panel: continuum intensity histogram of the pixels where the extra hump is seen on both the blue and the red lobe (thin-black), and the pixels where it is not seen on either lobe (thin-gray). For a better comparison, the vertical axis range is shortened from zero to 1000.