Appl. Sci. 2023 , 13 , 1389
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allows to achieve good contrast between the edge of the paper sample under examination and the background. In order to adjust the sharpness of the image, the camera is attached to the tripod via a setting sledge (5). This makes it possible to adjust the position of the camera in two horizontal axes—parallel and perpendicular to the optical axis of the camera. The camera lens allows to manually change the scale of reproduction in the range of 1 to 5, which gives the size of the recorded fragment of the paper sample in the range of 7.2mm × 5.8 mm to 36 mm × 24 mm. In the prepared measuring setup, magnifications in the range of 4 to 5 were used. Patterns of checkerboard (8) with a length of a single square of 1 mm (Figure 1b) were sticked to the fixed (6) and movable (7) clamps of the testing machine. It allowed to track the movement of the handle (6) and to determine the spatial resolution of the recorded images. The measurement begins by placing the tested paper sample (9) in the SCT holders of the testing machine, setting the desired focal length of the lens and positioning the camera in such a way that the sample and the checkerboard fragments containing at least two intersections between its fields are in the field of vision. Next, the force value is reset, the recording of the sequence of photos is started and after recording 3–4 images, the measurement is initiated in the machine. The measurement ends when the set displacement of the movable handle is reached. During the entire measurement, a recording of the sequence of images of the sample is performed along with fragments of handles with sticked checkerboards. 2.2. A Sequence of Operations Included in the Developed Measurement Technique The developed measurement technique consists of a series of operations that must be performed in order to obtain correct measurement results and their analysis. The flow diagram of the entire measurement is shown in Figure 2. The tested material and processed data are presented in the figure by means of gray rectangles. Operations included in the measurement process are shown in light blue rectangles with rounded corners.
Synchro- nisation measure ment data
Sample compression test in UTM
UTM measure- ment data
Conditio- ning the paper and preparing samples for testing
Measure- ment result: flow of measured quantities and estimated process parameters
Analysis of syn- chronis ed UTM data and images
Tested paper
Recording image sequence of tested
Image prepro- cessing
Sequence of images
sample images
Figure2. Flow diagram of the entire measurement procedure. 2.3. Developed Image Processing and Analysis Technique The recorded sequence of images was subjected to pre-processing and analysis. Pre- processing consisted of the following stages: • conversion of a series of RAW images to TIFF format with optional reducing the size of a digital image to reduce data volume, • extracting information about the recording time of each photo in the sequence with an accuracy of 1/100 of a second, • conversion of color images to grayscale,
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