Filters

Using Filters

Filters provide users with different methods of altering the appearance of documents and images. THis allows users to:

• Clean up scanned documents
• Make documents more readable
• Prepare documents for printing or distribution

The filters are found in a drop-down list by clicking Filter in the toolbar of the PDF and Image editor. Some filter options may not be available depending on the type of document that is open. For example, Invert Text is only available for black and white documents.

A filter may be applied to a single page or to all pages of a multi-page document. The first item listed in the Filter drop-down list is the Apply Filter to All Pages option. Click to the left to place a check mark next to the option and enable it and then select the appropriate filter. To select only one page of a document to have a filtered applied to, ensure that the Apply Filter to All Pages option is not checked, select the appropriate filter, and navigate to the document page to which you would like the filter applied.

Filters

Black and White (dithered)

Using this filter will turn a color image into black and white. "Dither" refers to the way pixels are displayed and dithering intentionally applies "noise" to an image. The Dithered filter is best when used with an image. The examples below show the dithering filter used on both text and an image.

Black and White (segmented)

Using this filter will turn a color document into black and white. Segmentation partitions the pixels within the image and is used to simplify and/or change the representation of an image into something that is more meaningful and easier to analyze.

Contrast

The Contrast filter is used to change the difference in brightness between the light and dark areas of a document. For example, if you set an image to a high-contrast level, there will be more shadows and highlights in the image; light-colored portions will become more light, and dark-colored portions will become more dark. If you set an image to a low-contrast level, the difference in brightness and darkness of the image will be reduced, and a black and white image will become gray throughout.

1. Click Filter | Contrast. A "Parameters for Adjusting Contrast" pop-up window will open.
2. Select a contrast value from -99 to 99 by using the arrows or typing in a value.
3. After a value has been entered, the preview pane will display the result of using the filter at the specified value. You may continue to change the contrast value until you achieve your desired result.
4. Click OK to apply the change shown in the preview pane to your document or click Cancel to discard the change.

Deskew

The Deskew filter is used to rotate a skewed, or slanted, document so that the alignment is corrected.

Note: This filter may take several minutes to complete its process.

Despeckle

The Despeckle filter is used to remove noise, or unwanted variations in brightness or color information, in a document. Noise is often thought of as the graininess of an image. The Despeckle filter removes the noise without blurring the edges of the document.

Dilate

The Dilate filter is used to widen and enhance the dark areas in a document. The boundaries of bright objects are dilated, or enlarged, and the boundaries of dark objects are reduced.

Note: If the Dilate filter is used on dark-colored text, then the text will appear more bold afterward.

Equalize Histogram

The Equalize Histogram filter is used to repair under-exposed documents. The Equalize Histogram filter redistributes the brightness values of the pixels to more evenly represent the entire range of brightness levels within the document.

Note: It is not recommended to use the Equalize Histogram filter with text documents as the result will make the text more difficult to read.

Erode

The Erode filter is used to minimize the dark areas of a document.

Note: If the Erode filter is used on dark-colored text, then the text will appear less bold afterward. If the Erode filter is used on light-colored text, then the text may not be visible at all.

Filp Horizontal or Vertical

Two filters allow you to reorient your document: Flip Horizontal and Flip Vertical. The Flip Horizontal filter flips the image or scanned document along its x-axis, meaning that what was on the left will be on the right and vice versa. The Flip Vertical filter flips the image or scanned document along its y-axis, meaning that what was on the top will be on the bottom and vice versa.

Grayscale

The Grayscale filter converts color images to images with up to 256 shades of gray.

Black and White vs. Grayscale

It is important to recognize that grayscale images and black and white images are not the same. While grayscale utilizes 256 shades of gray, black and white images only use black and white. Grayscale is typically used to remove the color from an image, while black and white is often used to remove color from a plain-text document.

Invert

The Invert filter is used to invert the colors on an image or document. If you use the Invert filter on a document with a white background and black text, the black text would become white and the white background would become black.

Invert Text

Select the Invert Text filter to change white text on a black background to black text on a white background. This is useful for keeping complex documents consistent. For example, if the header of a scanned document is encased in a black box, the PDF and Image Editor can simplify the header by removing the black box and making the text black.

The Invert Text filter only works on white text in a black bounding box that is surrounded by a white background.

Tip: If this option is not available, use either the Black and White (dithered) or the Black and White (segmented) filter first.

1. Click Filter | Invert Text.
2. Set the parameters for removing lines by entereing or selecting the values in the following fields:
   • Minimum Width (pixels): Specify the minimum width of the black bounding box you want to invert.
   • Minimum Height (pixels): Specify the minimum height of the black bounding box you want to invert.
   • Minimum Black (percent): Specify, in percent, the minimum amount of black in the bounding box you want to invert.
   • Maximum Black (percent): Specify, in percent, the maximum amount of black in the bounding box you want to invert.
3. Click OK. The text is inverted.

Remove Border

Select this filter to remove a border from a black and white image. This filter will not work for an image that is not black and white.

Tip: If this option is not available, use either the Black and White (dithered) or the Black and White (segmented) filter first.

1. Click Filter | Remove Border. A window opens.
2. Set the parameters for removing borders by entering or selecting values in the following fields:
   • Side of Page: Select which side of the page you would like the border removed from by selecting from the drop-down list provided.
   • Minimum Portion of Page (percent): Specify, using percent, how much of the side of the page you want removed.
   • Maximum Diameter of Noise (pixels): Specify the maximum diameter of noise that is in the border. For example, if your border had some specks of white in it, then use this function to remove those specks.
3. Click OK. The borders are removed from the sides specified.

Remove Holes

Hole punches often show up as black circles on scanned documents. The Remove Holes filter allows you to remove these black circles. This filter will not work for an image that is not black and white.

Tip: If this option is not available, use either the Black and White (dithered) or the Black and White (segmented) filter first.

1. Click Filter | Remove Holes. A window opens.
2. Specify the parameters for removing holes by selecting or entering values for the following fields:
   • Side of Page: Select the side of the page that the holes are on from the drop-down list.
   • Minimum Holes: Specify the minimum amount of holes by typing in a number or moving the slider.
   • Maximum Holes: Specify the maximum number of holes by typing in a number or moving the slider.
   • Minimum Hole Diameter (pixels): Specify the minimum hole diameter by typing in a number or moving the slider.
   • Maximum Hole Diameter (pixels): Specify the maximum hole diameter by typing in a number or moving the slider.
3. Click OK.

Remove Lines

Select this filter to remove lines from a black and white image. This filter will not work for an image that is not black and white.

Tip: If this option is not available, use either the Black and White (dithered) or the Black and White (segmented) filter first.

Click Filter | Remove Lines. A window opens.

Specify the parameters for removing holes by selecting or entering values for the following fields:

• Orientation: Indicate the direction that the lines run on the page. For example, if the lines ran from the top of the page to the bottom you would select Vertical.
• Minimum Line Length (pixels): Specify the minimum length of the lines you want to remove.
• Maximum Line Width (pixels): Specify the maximum width of the lines you want to remove.
• Maximum Gap Length (pixels): Specify in pixels the maximum gap that exists between the lines that you want to remove.

Click OK. The lines are removed from the document.

Threshold

The Threshold filter is used to convert a grayscale or color document to a binary, or black and white, document based upon a threshold value. The threshold value is set based upon a pixel intensity value. If a pixel in an image has an intensity value less than the set threshold value, then the corresponding pixel in the resultant image will be set to black. If a pixel in an image has an intensity value greater than or equal to the set threshold value, then the corresponding pixel in the resultant image will be set to white.

1. Click Filter | Threshold. A pop-up window will open.
2. Select a pixel cutoff value from 1 to 255 by using the arrows or typing in a value. After a value has been entered, the preview pane will display the result of using the filter at the specified value. Continue to change the threshold value until you achieve your desired result.
3. You can either apply or discard the change.
   • If you would like to apply the change shown in the preview pane to your document, click OK.
   • If you would like to discard the change shown in the preview pane, click Cancel.