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uScope Navigator (Filter Manager)

Level Clipping to Improve Flat Field
uScope Navigator (Filter Manager)

Information in this article applies to:

  • uScope Navigator V4.3 and Later

Article ID: NFL1133 — Created: 28 Jan 2018 — Reviewed: 11 Mar 2018

Symptom

Image with Poor Flat-FieldOn occasion, deep zoom images may exhibit artifacts that make each field clearly apparent. While the effect is not visible on an individual field, the repeating pattern visible in a scanned region of interest is dramatic and distracting.

Cause

These artifacts are generally referred to as flat-field effects. They are caused by a gradient (or lack of flatness) in the illumination field and are caused by any of a number of things. Fortunately, the level clipping filter can be used to mitigate many flat field issues.

Resolution

Using the Level Clipping Filter is very effective. But, it requires a number of steps to complete. You must first, determine the proper white clipping level. Then, you must create a Deep Zoom filter sequence using that level. And, finally, you must create a new deep zoom image from your scan using the newly created filter.

Determining the Proper White Clipping Level

  1. Level Clipping FilterStart with a Deep Zoom image from your scanned region of interest.
  2. Open the Deep Zoom image in the Deep Zoom Viewer.
  3. Open the Filter Settings dialog from the Deep Zoom Viewer, make certain Clip to White is unchecked, and slowly drag the right handle (above the 255 indicator) to the left. Once the handle is selected, you may use the cursor keys to move it one pixel value at a time.
  4. Continue to lower the white clipping level until the background levels out.
  5. Write down or remember the white clipping level. In this example, it is 230.
  6. Exit the Deep Zoom Image Viewer.

Creating a Deep Zoom Filter Sequence

  1. Create New FilterFrom the uScope Navigator main screen, open the Filter Manager.
  2. Click the New button under Filter Strategy and enter a name for the new filter.
    We chose LC-230 for the name of our example filter.
  3. For the Create Type selection, be sure to choose Deep Zoom.
  4. Click the Create button.
  5. Click the + button beside the Filter Steps block and select the Level Clipping filter.
    Add Filter Step
  6. When the Level Clipping filter is added, you may adjust its parameters. Set the White clipping level to 230 and the Black clipping level to 1. Be sure to un-check Clip to White.
    Set Clip Levels
  7. Finally, click the Save button under Filter Strategy to save the filter.

Using the Filter to Create a Deep Zoom Image

  1. Create Deep Zoom using FilterSelect the Scan Job from the Job Manager or use the existing scan job from the uScope Control Panel.
  2. Then, click the Create Deep Zoom button to open the Create Deep Zoom dialog.
  3. Select the filter you just created for the Image Filter (LC-230 for this example).
  4. Click the Create Deep Zoom button to start building the deep zoom image.
  5. When the Deep Zoom image is created, you should notice that the flat-field artifacts have been eliminated by the Level Clipping filter.
    Image with Level Clipping Filter

Note
You may wish to adjust the Deep Zoom filter settings to better suit your taste in image quality. If so, open the Deep Zoom Filter from the Filter Manager and adjust the filter settings. You may also add additional filters (like brighten, contrast, gamma, or sharpen) to the sequence.

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