Modify "to_rgb" loop in mineral.py to use numpy.where

[Jonathan Luner]

This loops through each of the pixels and checks to see if the pixel has data. If it does not, it sets the pixel's value to 0.

#remove no data pixels
for band in [red_band, green_band, blue_band]:
    for x in range(band.shape[0]):
        for y in range(band.shape[1]):
            if numpy.isclose(band[x, y, 0], -0.005) or band[x, y, 0] == -50:
                band[x, y] = 0

This takes a large amount of time as running this on the large example file will take around 20 minutes. Changing this loop to a numpy.where operation could significantly reduce runtime.

[Lewis John McGibbney]

+1

[Jonathan Luner]

Currently working in branch: "Issue-187". Currently runs through to_rgb loop in a few seconds instead of 20 minutes for the large example file. Compared results in QGIS and everything appears to work as expected.