The original color picture

The picture converted by Photoshop mode changing (RGB->Grayscale)
Note that red dots on the hill become invisible.

Red channel of the original image.

Green channel of the original image.

Blue channel of the original image.

Image produced by blending green and red channels (60 and 40 percents, respectively).

Some other image would require other percentages/channels/channel curves to produce the adequate B/W representation.