Digital Light & Color

Trying to understand how the Mask Brightness Curve button influences the Curve function, for masking in the Composite transform (2 images).

As a test - On the base image, I applied a mask, initially using the Curve button so the mid-tones were selected (two end points lower corners, two points on the bottom about a quarter of the way in from the ends, two points along the top just inside the two lower points). So, like an upside down "U".

I then used the Mask Brightness Curve to alter the first mask. This curve was for the dark tones, essentially splitting the tones of the first mask, down the middle (curve line like a straight walled "Z"). I presumed (apparently incorrectly) that the new mask would further constrain the first masked area to just the darker parts of that masked area. However when I clicked apply, it actually inverted the entire first mask to where, what had been initially selected in the image was now not selected and what had initially not been selected was now selected. This was regardless of whether the new masked areas were light or dark, it masked both. Is this correct?

Marv

The Mask Brightness Curve tool applies a brightness curve to the current mask. This would commonly be used to increase or decrease the contrast of the current mask or make part of it more or less transparent (darker or lighter). It does not act on the previous curve but rather on the current mask or change what parts of the tonal range are selected. The Mask Brightness Curve you applied inverted the previous mask.

To refine the previous curve, either undo the curve and try again with a new curve, or apply a second curve to add or remove parts of the tonal range of the image, based on the mask mode.