Abstract— In the field of microbiology, the counting of
bacterial colonies is fundamental and mandatory. This is done to
estimate the number of bacterial cells in every 1 milliliter or gram
of sample. The counting takes a long time and is tedious, so it
requires an accurate and fast counting method. The image quality
used is very low and contains noise. Therefore, a preprocessing
method is needed to reduce the noise. The Perona-Malik filter
method is known to be able to remove noise well. However, it is
difficult to determine the appropriate gradient threshold
parameter (k) for each different image. To find the appropriate
value of k, the original Sobel Mask method and Sobel Mask
Fractional-Order are used to estimate the value of k. The
experimental results show the results of noise reduction using
PMD with a value of k from the original Sobel Mask and Sobel
Mask Fractional-Order. The results of the accuracy of
determining the value of k with the Sobel Mask Fractional-Order
(α=1.0) show higher results based on the F-Measure values for
samples 1, 2, and 3 respectively 97%, 98%, and 90%.