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 steepness of the slope at that point is given by the magnitude of the gradient vector. The gradient can also be used to measure how a scalar field changes in other directions, rather than just the direction of greatest change, by taking a dot product. Suppose that the steepest slope on a hill is 40%.If a road goes directly up the hill, then the steepest slope on the road will also be 40%.onsider a room in which the temperature is given by a scalar field, T, so at each point (x, y, z) the temperature is T(x, y, z) . (We will assume that the temperature does not change over time.) At each point in the room, the gradient of T at that point will show the direction the temperature rises most quickly.