An indicator is a large organic molecule that works somewhat like a  color dye. Whereas most dyes do not change color with the amount of acid or base present, there are many molecules, known as acid - base indicators, which do respond to a change in the hydrogen ion concentration. Most of the indicators are themselves weak acids. The most common indicator is found on litmus paper.
The magnitude of the gradient tells us how quickly the image is changing, while the direction of the gradient tells us the direction in which the image is changing most rapidly. To illustrate this, think of an image as like a terrain, in which at each point we are given a height, rather than an intensity.e will see that the gradient allows us to answer this question. Letâs consider how the image changes as we move from position (x,y) by a small amount, â, in an arbitrary direction Î¸, which will take us to the position (x+ â cos Î¸, y + â sin Î¸). At (x,y) the image intensity is I(x,y) .
The gradient of a straight line is the number of co-ordinates on the y axis to one co-ordinate on the x axis.he gradient of a straight line is the number of co-ordinates on the y axis to one co-ordinate on the x axis.