For example, when the sky is overcast, the image is dark, leading to a smaller range of pixel values and less likelihood of picking up differences that signify ridge lines. A scaling of the pixel values can often widen the spread, but only if there are not too many outliers to skew the distribution. As an example, an image taken with an overcast sky might contain pixels in the range of 0 to 150. By scaling the pixel values, the range can be changed to 0 to 255, providing a larger difference in values along the ridge lines. However, a patch of white in the image, such as a piece of pavement in the foreground, produces outliers and will skew the distribution and mitigate the effect of the scaling.
Vegetative growth can also change the look of the surroundings.
A tree line may be mistaken as a ridge line when analyzing the digital image. However, it should be noted that human navigators also occasionally mistake tree lines for ridge lines.