This doesn't seem to be enough of a difference to account for the absorbtion line in the smaller bandwidth, so it's probably the theoretical blackbody (Plank) curve's intensity. The absorbtion line would result in a far greater a difference, and it is the absorbtion line which provides the "window" to see the relatively faint glow of the chromosphere.

To carry the analogy further: outside of this window, opaque "shutters" are needed to block the side band energy - this is what narrow band solar H alpha filters do - completely block the side band energy from the photosphere and allow us to see into the window where a candle is burning. Broad band filters let a portion of this side band energy through.

Using a white light filter to reduce the side band energy is like pulling a dark shade over the side of the house - it greatly reduces the side band energy, but also prevents us from viewing through the window to see the candle.