Operations on Images#

This section describes the operations that can be performed on images.

See also

Processing Images for more information on image processing features, or Computing features on Images for information on computing features on images.

../../_images/i_operation.png

Screenshot of the “Operations” menu.#

When the “Image Panel” is selected, the menus and toolbars are updated to provide image-related actions.

The “Operations” menu allows you to perform various operations on the current image or group of images. It also allows you to extract profiles, distribute images on a grid, or resize images.

Basic arithmetic operations#

Operation

Description

sum Sum

\(z_{M} = \sum_{k=0}^{M-1}{z_{k}}\)

average Average

\(z_{M} = \dfrac{1}{M}\sum_{k=0}^{M-1}{z_{k}}\)

difference Difference

\(z_{2} = z_{1} - z_{0}\)

quadratic_difference Quadratic difference

\(z_{2} = \dfrac{z_{1} - z_{0}}{\sqrt{2}}\)

product Product

\(z_{M} = \prod_{k=0}^{M-1}{z_{k}}\)

division Division

\(z_{2} = \dfrac{z_{1}}{z_{0}}\)

Operations with a constant#

Create a new image which is the result of a constant operation on each selected image:

Operation

Equation

constant_add Addition

\(z_{k} = z_{k-1} + conv(c)\)

constant_substract Subtraction

\(z_{k} = z_{k-1} - conv(c)\)

constant_multiply Multiplication

\(z_{k} = conv(z_{k-1} \times c)\)

constant_divide Division

\(z_{k} = conv(\dfrac{z_{k-1}}{c})\)

where \(c\) is the constant value and \(conv\) is the conversion function which handles data type conversion (keeping the same data type as the input image).

Real and imaginary parts#

Operation

Description

abs Absolute value

\(z_{k} = |z_{k-1}|\)

re Real part

\(z_{k} = \Re(z_{k-1})\)

im Imaginary part

\(z_{k} = \Im(z_{k-1})\)

Data type conversion#

The “Convert data type” convert_dtype action allows you to convert the data type of the selected images.

Note

Data type conversion relies on numpy.ndarray.astype() function with the default parameters (casting=’unsafe’).

Basic mathematical functions#

Function

Description

exp Exponential

\(z_{k} = \exp(z_{k-1})\)

log10 Logarithm (base 10)

\(z_{k} = \log_{10}(z_{k-1})\)

Log10(z+n)

\(z_{k} = \log_{10}(z_{k-1}+n)\) (avoid Log10(0) on image background)

Other operations#

Flat-field correction#

Create a new image which is flat-field correction of the two selected images:

\[\begin{split}z_{1} = \begin{cases} \dfrac{z_{0}}{z_{f}}.\overline{z_{f}} & \text{if } z_{0} > z_{threshold} \\ z_{0} & \text{otherwise} \end{cases}`\end{split}\]

where \(z_{0}\) is the raw image, \(z_{f}\) is the flat field image, \(z_{threshold}\) is an adjustable threshold and \(\overline{z_{f}}\) is the flat field image average value:

\[\overline{z_{f}}= \dfrac{1}{N_{row}.N_{col}}.\sum_{i=0}^{N_{row}}\sum_{j=0}^{N_{col}}{z_{f}(i,j)}\]

Note

Raw image and flat field image are supposedly already corrected by performing a dark frame subtraction.

Rotation#

Create a new image which is the result of rotating (90°, 270° or arbitrary angle) or flipping (horizontally or vertically) data.

Intensity profiles#

Line profile

Extract an horizontal or vertical profile from each selected image, and create new signals from these profiles.

../../_images/i_profile.png

Line profile dialog. Parameters may also be set manually (“Edit profile parameters” button).#

Segment profile

Extract a segment profile from each selected image, and create new signals from these profiles.

Average profile

Extract an horizontal or vertical profile averaged over a rectangular area, from each selected image, and create new signals from these profiles.

../../_images/i_profile_average.png

Average profile dialog: the area is defined by a rectangle shape. Parameters may also be set manually (“Edit profile parameters” button).#

Radial profile extraction

Extract a radial profile from each selected image, and create new signals from these profiles.

The following parameters are available:

Parameter

Description

Center

Center around which the radial profile is computed: centroid, image center, or user-defined

X

X coordinate of the center (if user-defined), in pixels

Y

Y coordinate of the center (if user-defined), in pixels

Distribute images along a grid#

Feature

Description

distribute_on_grid Distribute on a grid

Distribute selected images on a regular grid

reset_positions Reset image positions

Reset the positions of the selected images to first image (x0, y0) coordinates