image processing and enhancement

Graphic Workshop's View mode includes a rich library of image processing filters which can be interactively applied to graphics to improve their appearance. You may find them helpful in adjusting marginal images to make it more apparent what they depict; to resize or transform graphics for presentation and to improve the clarity of pictures which have been deliberately degraded to make it less obvious what they contain.

Not all the filters in the Graphic Workshop filter library will be of use in forensic applications. Some of them are special effects, for other applications.

To access the filter library:

  1. Double-click on the image you'd like to process in a Graphic Workshop browser window, to open it in View mode.
  2. Click on the Swiss army knife button in the View mode tool bar, or select Filters from the Picture menu. The Filters dialog will open.
  3. Select the filter you wish to apply to your image from the combo box in the upper left corner of the Filters dialog, and adjust the appropriate parameters.
  4. Click on Preview. The left image window will show you your graphic prior to processing with the filter you have selected, and the right window will show you your graphic after it has been processed.
  5. If the results of your filter are not what you had in mind, adjust the filter and preview the filter again.
  6. When your selected filter has been configured to produce the results you need, click on OK to apply your filter to the image in View mode.

Here are a few things to keep in mind about the Filter function:

  • There's help available for each of the filters, to explain in detail what their controls do and what the filters themselves are intended to accomplish. Select a filter in the Filters dialog and click on Help.
  • You can apply multiple filters to the same image, one after another. Just open the Filters dialog a second time.
  • Having filtered an image, the changes you've made will apply only to the image on your monitor. They won't be saved to disk unless you tell Graphic Workshop to do so. To save a processed image to disk, select Save or Save As from the Picture menu in View mode. The former will save your image back to the file it was read from. The latter will prompt you to choose a new file name and format to save it to.
  • If you apply a filter to an image and then change your mind, you can restore the graphic in View mode to its pre-filtered state. Select Undo from the Picture menu.
  • If you apply a filter to a graphic in View mode and then close View mode without first selecting Save or Save As from the Picture menu, the changes made by your filter will be discarded.

Here are a few of the filter functions you might find useful in forensic applications:

Color and Intensity: Adjust the color balance and brightness of an image to correct for intentional or accidental color shifts, or poor exposure settings.

Contrast and Brightness: Adjust the contrast and brightness of an image to correct for poor exposure settings.

Equalize: Redistribute the highlights and shadows of an image to make it easier to see.

Flip: Flip an image horizontally or vertically.

Gaussian Blur: Not all that helpful by itself, blurring an image can be useful in reducing moiré patterns. When a mechanically-screened image -- such as a photograph printed in a book or a magazine - is reproduced with a digital scanner, the image can be overlaid with a regular interference pattern, or "moiré." It's typically impossible to remove a moiré entirely once it's been created, but you can usually reduce its effect, and make the underlying image more readable, by first blurring the image slightly with the Gaussian Blur filter, and then using the Sharpen filter to un-blur it. Plan to experiment to get a feel for how to use this technique.

Hue Saturation and Brightness: This is an alternate color model for adjusting the color of images. You might find it more intuitive than the Color and Intensity filter.

Invert Colors: This filter turns images into negatives. More to the point, it turns images that have been deliberately turned into negative to make them less easily identified back into positives.

Normalize: This filter will increase the contrast of an image as much as possible, to make it as viewable as possible. It's a quick way to enhance washed-out or poorly exposed pictures.

Resize: This filter will resize your graphics - it's helpful if you're creating graphics for a printed document or a PowerPoint presentation, for example.

Rotate: This filter will rotate your graphics by any amount, adjustable to one degree.

White Balance: This filter will locate the lightest pixel in an image and adjust color of the entire image by the amount needed to make the lightest pixel pure white. It's a quick way to improve badly exposed pictures.

There are a great many other filters available in the Graphic Workshop filter library. The Reference document lists them all.