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The Flatten command eliminates unwanted features from scan lines (e.g., noise, bow and tilt). It uses all unmasked portions of scan lines to calculate individual least-square fit polynomials for each line. |
Flatten is useful prior to image analysis commands (e.g., Depth, Roughness, Section, etc.) where the image displays a tilt, bow or low frequency noise, which appear as horizontal shifts or stripes in the image. |
Figure 1: Image with Bow
Figure 2: Image with Bow Removed
The Flatten command is a filter that modifies the data to delete low frequency noise and remove tilt from an image. Each line is fit individually to center data (0th order) and remove tilt (1st order), or 2nd or 3rd order bow. A best fit polynomial of the specified order is calculated from each data line and then subtracted out. In some cases, the stopband (box cursor to exclude features) can be used to remove regions of the image from the data set used for the polynomial fits. Click on the image to start drawing a stopband box. Right-click on a box to delete it or change its color.
The polynomial equations calculate the offset and slope, and higher order bow of each line for the data as per the table below.
Order | Polynomial | Explanation |
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0 | z = a | Centers data along each line. |
1 | z = a + bx | Centers data and removes tilt on each line (i.e. calculates and removes offset (a) and slope (b). |
2 | z = a + bx + cx 2 | Centers data and removes the tilt and bow in each scan line, by calculating a second order, least-squares fit for the selected segment then subtracting it from the scan line. |
3 | z = a + bx + cx2 + dx3 | Centers data and removes the tilt and bow in each scan line, by calculating a third order, least -squares fit for the selected segment then subtracting it from the scan line. |
Table 1: Flatten Polynomials
For an image that contains a number of noisy scan lines, use the Flatten command to correct the problem. | |
Select an image file from the file browsing window at the right of the main window. Double click the thumbnail image to select and open the image. |
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Figure 3: Select Flatten from the Workspace.
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Click the Flatten icon in the toolbar. |
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Figure 4: Image of tip check sample before (left) and after (right) 0th order Flatten operation
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A series of parameters appear in the Flatten view, allowing the order of the Flatten polynomial to be selected and display parameters to be adjusted.
Figure 5: Flatten view—single monitor
Parameter | Description |
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Flatten Order selects the order of the polynomial calculated and subtracted from each scan line. Settings:
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Specifies the range of data to be used for the polynomial calculation based on the distribution of the data in Z: Range or Settings:
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Applies the Thresholding values for the whole image or each line independently. Range or Settings:
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Flatten Z Threshold % |
Defines a Z value as a percentage of the entire Z range in the image (or data set) relative to the lowest data point. |
Output File Name |
Specifies the name of the file to be created. Leave blank for immediate view/use without saving the altered image file. |
Write File Upon Execute |
Writes the output file when the Execute button is clicked. |
Table 2: Flatten Range, Settings and Buttons
Parameter | Description |
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Execute |
Initiates the Flatten command, based on the order selected.. |
Reload |
Restores the image to its original form by reloading the original file. |
Table 3: Buttons on the Flatten Panel
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