DPCM is lossless Predictive Coding:
In DPCM, Interpixel redundancy exists due to the correlation between the neighboring pixels in an image. Spatial redundancy implies that there is a relationship between pixels in an image. The value of any given pixel can be predicted from the value of its neighbors that is they are highly correlated. The information carried by individual pixel is relatively small. To reduce the inter-pixel redundancy the difference between adjacent pixels are used to represent an image
The difference between the incoming pixel and its predicted value is obtained. For digital images, the signal is processed line by line, thus two dimensional signal is represented by one dimensional signal f(x)
The error signal is obtained by subtracting the previous sample value from the current input sample value. e(x) =f(x) – f’(x)
The error signal is further coded using variable length coding.
As shown in figure above DM encoded signal is first decoded to give e(x).
Predicted signal value is added to give reconstructed input image sample value. f[x]=e[x]+f’[x]