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Digital Image Processing (2000)

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User's Guide / Point Operations /
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Image Modification by Point Operations

3.1 Introduction

Point operations constitute a simple but important class of image processing operations. These operations change the luminance values of an image and therefore modify how an image appears when displayed. The terminology originates from the fact that point operations take single pixels as inputs. This may be expressed as
where T is a grayscale transformation that specifies the mapping between the input image f and the result g. Point operations are a one-to-one mapping between the original (input) and modified (output) images according to some function defining the transformation T. Sections 3.2 and 3.3 introduce the basic concepts of quantization (or luminance resolution) and the histogram, an important and widely used representation of the raw image data. Examples of useful grayscale transformations will be given in Sections 3.4, and 3.5. Point operations are also known as zero-memory operations. Point operations are typically used for simple contrast enhancement purposes such as contrast stretching, quantization, color transformations, and false color methods.