Arithmetic and Logic

Non-exhaustive list of reasons one may use arithmetic and logic operations:

• To emphasize differences between images by subtracting the pixels (a conformity check).

• To compensate for non-uniform lighting by dividing the target image by the image of the background alone.

• To remove unwanted areas of an image by preparing an appropriate mask, and clearing all the pixels that belong to the mask by using logical combinations of pixels.

• To create a combined image by combining the pixels of two source images to generate a resulting image.

Arithmetic operations are handled by the EasyImage::Oper ^{.NET Python} function, EArithmeticLogicOperation ^{.NET Python} enum lists all supported operators.

These operations can be applied to images and constants, they have one or two source arguments (image or integer constants) and one destination argument. If the source operands are a color and a gray-level image, each color component combines with the gray-level component to give a color image. Histogram equalization can improve your results.

Arithmetic and Logic Combinations

All possible operations are classed in seven categories in this documentation, and all operations for each category are detailed later.

• General

• Copy

• Invert

• Shift

• Logical

• Overlay

• Set

Allowed Combinations of Input(s) and Output

Input(s)	Output	General	Copy	Invert	Shift	Logical	Overlay	Set
EBW8 constant	EImageBW8		✓
EC24 constant	EImageC24		✓
EImageBW8	EImageBW8		✓	✓
EImageBW8	EImageC24		✓	✓			✓
EImageC24	EImageC24		✓	✓
EBW8 constant and EImageBW8	EImageBW8	✓
EImageBW8 and EBW8 constant	EImageBW8	✓			✓			✓
EImageBW8 and EImageBW8	EImageBW8	✓				✓		✓
EImageBW8 and EImageBW8	EImageC24	✓					✓
EC24 constant and EImageC24	EImageC24	✓
EImageC24 and EC24 constant	EImageC24	✓			✓
EImageC24 and EImageC24	EImageC24	✓				✓
EImageC24 and EImageBW8	EImageC24	✓				✓	✓
EImageBW8 and EImageC24	EImageC24	✓				✓		✓

Note

For logical operators, a pixel with value 0 is assumed false, otherwise true. The result of a logical operation is 0 when false and 255 when true.

General Operations

Compare (abs. value of the difference) Saturated sum Saturated difference Saturated product Saturated quotient Modulo Overflow-free sum Overflow-free difference Overflow-free product Overflow-free quotient

Bitwise AND Bitwise OR Bitwise XOR Minimum Maximum Equal Not equal Greater or equal Lesser or equal Greater Lesser

Copy Operations

• Copy EArithmeticLogicOperation_Copy ^{.NET Python}

  • Copies a constant to all the pixels of an image. Useful, for example, to initialize a newly created image.

  • Copies an image to another image.

Invert Operations

• Invert EArithmeticLogicOperation_Invert ^{.NET Python}

  • When not specifying a constant, the image is inverted into the destination image. Which means, each pixel channel value is computed as \(255 - pixelChannelValue\)

  • Otherwise, when a constant is specified, it is computed as \(constant - pixelChannelValue\)

Shift Operations

• Left Shift EArithmeticLogicOperation_ShiftLeft ^{.NET Python}

• Right Shift EArithmeticLogicOperation_ShiftRight ^{.NET Python}

Logical Operations

• Logical AND EArithmeticLogicOperation_LogicalAnd ^{.NET Python}

• Logical OR EArithmeticLogicOperation_LogicalOr ^{.NET Python}

• Logical XOR EArithmeticLogicOperation_LogicalXor ^{.NET Python}

Overlay Operations

• Add an overlay EArithmeticLogicOperation_Overlay ^{.NET Python}

Set Operations

This operation involves three images.

• Source Image: that will be conditionally copied to Destination Image.

• Mask Image: that will set whether a pixel from Source Image must be copied to Destination Image.

• Destination Image: whose pixels will equal pixel from Source Image if mask image pixel is

  • Equal to zero when using EArithmeticLogicOperation_SetZero ^{.NET Python}

  • Different from zero when using EArithmeticLogicOperation_SetNonZero ^{.NET Python}

  • Otherwise, the pixel value is unchanged.

C++

EasyImage::Oper(EArithmeticLogicOperation_SetZero, &sourceImage, &maskImage, &destinationImage);

C#

EasyImage.Oper(EArithmeticLogicOperation.SetZero, sourceImage, maskImage, destinationImage);

Python

EasyImage.Oper(EArithmeticLogicOperation.SetZero, sourceImage, maskImage, destinationImage);

Note

For logical operators, a pixel with value 0 is assumed false, otherwise true. The result of a logical operation is 0 when false and 255 when true.

See Also

Code Snippets

Easy to understand, ready to copy code snippets.

Arithmetic and Logic Operations