This module is intended for image pre-processing. The following modifications are available in this module:


Cut lets you crop the image manually from all four sides.

Local Image


Scale lets you adjust the resolution of the image.

Local Image


You can rotate all images by a specified angle.

Local Image

Background normalization

Background normalization serves for unifying colors.

Local Image


This functions blurs the picture and reduces noise. Details in the OpenCV documentation.

Local Image

Canny edge detector

Canny edge detector focuses only on the outlines of the objects. Here you can set Threshold value to highlight the outlines. Details in the OpenCV documentation.

Local Image

Remove background

Remove background function can help you with focusing only on the main object. Offers two types of background removal (histogram and canny), each can be useful for different kinds of images. The ‘Canny background removal’ uses canny edge detector, dilation and erosion.

Local Image


Unifies the position and angle of objects or just puts the angle of the object into Context (if this option is ticked). Remove background needs to be used before Unifier.

Local Image

Contrast equalisation

Equalises the contrast using the CLAHE algorithm, which works with a histogram of a pixel and its surroundings (depending on the kernel size). Clip limit determines the value at which the histogram is clipped. Details in the OpenCV documentation for CLAHE and histogram equalisation.

Local Image


Can be used to expand shapes found in the input image. Details in the OpenCV documentation for dilate and morphological transformations.

Local Image


Can be used to reduce shapes found in the input image. Details in the OpenCV documentation for erode and morphological transformations.

Local Image

Polar transform

Finds the biggest circle in the image (found circle can be seen in the left image showing the ‘Stage 1’ layer of polar transform), then transforms it using polar coordinates. ‘Minimal distance between circles’ can be used to adjust how many circles will be found by defining a minimal distance which needs to be between their centers. The ‘inverse ratio of the accumulator/image resolution’ is used to adjust accumulator resolution (the lower the ratio, the higher the accumulator resolution). Details in the OpenCV documentation for Hough circles and polar warp.

Local Image

Color space transform

Converts the image into a different color space (HLS, HSV, YUV, LAB or GRAY). Details in the OpenCV documentation.

Local Image

Adjust gamma

This function lets you adjust the gamma value. Local Image

Kernel size

Some transformations use a parameter called ‘Kernel size’, which determines the size of the matrix of surrounding pixels, which are taken into consideration when computing the transformation.


Using the ‘Active’ checkbox, the whole module can be enabled or disabled. You can also enable/disable each function individually. When new module or individual function is created, it is automatically set as active.

Order of functions, changing layers

Individual functions are applied one after another from the top. You can change the order of the functions so that they suit your needs best, just drag and drop them to the right place. If you want to see how the image looks after applying individual active modifications (and its stages in some cases), you can change layers using the button at the top, which is set to ‘Show all layers’ by default.

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