Video ToolBox Ultra workflow for yellow printer dots

Workflow Design -- Configuring Video ToolBox Ultra for working with yellow printer dots

Video ToolBox Ultra has a wide range of tools for working with live images including transparent overlays, live measurement and annotation tools, real-time color space conversion, side-by-side comparison and much more. To use all of these tools to compare the yellow dot patterns of multiple documents, we suggest the following workflow:

Note 1: A video demonstration of this workflow can be seen at: https://vimeo.com/1204266160

Workflow Outline

Optimize Computer and Software Performance

Video ToolBox Ultra offers a wide range of tools which are useful for analyzing yellow printer dots, including live color space conversion, transparent overlays, and live measurement tools. On most computers, the software can perform each of these functions with enough speed and immediacy to be called real-time. If you are going to use all of these features at the same time, then it may be necessary to change some settings to maximize the performance of the software. We recommend the following:

1. Make sure your video device is connected to your computer and start the Video ToolBox Ultra software.

2. Adjust any camera settings to optimize the image quality. Set up any other accessories so that you are ready to work with the documents that contain the yellow printer dots.

   Resolution

3. Reduce the camera resolution to the minimum that still gives sufficient resolution to clearly see the yellow printer dots.

   

We find that 1280 x 720 pixels works well to balance resolution with performance, but if you are using a newer computer, then you may be able to get good performance at even higher resolution. 

Detection

4. Turn on live color space by pressing the COLOR button. This will display the color space window

Above is a summary of the interface: Click the "Select Color Space" menu to choose a color space format. Check the "Enable Display Controls" checkbox to display additional controls to enhance the live image display with offset and contrast sliders. Use the inverse checkbox to display the negative image (where colors space values are reversed).

You can learn more about the live color space software controls by downloading the abbreviated instructions: colorspaceinstructions.pdf

We recommend two color spaces for visualizing yellow printer dots: HSV -- saturation channel, or CIE Lab -- channel a.

The above image uses HSV - saturation color space. The yellow dots are more saturated than both the background white paper and the black printed text. As a result, the yellow dots stand out as bright spots against a dark background. Adjust the offset and contrast sliders to maximum the contrast between the dots and the background.

The above image uses the CIE Lab - a channel color space. The yellow dots appear darker than the background in this color space, so we use the inverse option in the Display Controls to display the dots as white on a dark background. Again, the offset and contrast sliders can help to maximize the brightness of the dots.

Displaying the printer dots as bright will help when two documents are overlayed to compare the dot patterns -- as will be seen when the software is configured for overlay comparison (next).

Two other color spaces that might also help to visualize the yellow printer dots are RGB - blue channel, and CMYK - yellow channel. These color spaces are not shown here, but it is easy to switch between the different color space options in Video ToolBox Ultra to compare which displays the yellow dots most clearly.

Overlays

5. A useful forensic document analysis would be to compare the yellow dot patterns on different pages of the same document (to detect page insertions) or on the pages of different documents (to evaluate if the documents were printed on the same printer). Video ToolBox Ultra software includes a range of tools for overlaying a saved image, or clipboard image, directly on the live image, to make these types of comparisons. This allows you to store a reference image (a yellow printer dot pattern) and then compare live document images by simply dragging documents under the camera or handheld microscope to compare the patterns.

To setup the software for this workflow, we need to save a reference image in our preferred color space. Setup the sample so that the yellow dot pattern is centered on the screen, and select a color space so that the dots are prominently displayed as bright dots on a dark background (as shown in figure (22) and (23)). Make sure that the Capture Mode is set to image capture (the camera icon at the left), note the name of the next image that will be captured (shown at the bottom-left of the status bar), and press the CAPTURE button. The reference image is now captured and ready to be used as an overlay. Press the OVERLAY button and select Graphic Overlay --> Graphic Overlay Settings... to open the settings window seen here.

Configure the settings window as follows:

1. Press the set button and select the file to be used as the overlay. This should be the file that was just captured.

2. Set the scaling to 1X so that the overlay matches the size of the live image.

3. Select Transparent Overlay to start.

4. Set the transparency to 50% to start.

5. Press the Load Overlay button to display the overlay.

The overlay should now be displayed on the live image. You can check that the overlay is being displayed by moving the sample slightly -- which will shift the dot pattern as compared to the overlay. You can also move the overlay by holding down the SHIFT key while clicking and holding the left mouse button, and then slowing moving the mouse. This shifts the position of the overlay. While holding down the SHIFT key, double-click the left mouse button to move the overlay image back to its default position.

Here is what you would see for a transparent overlay of printer dots imaged in HSV - saturation color space.

Note that there are two dots at each location -- one for the saved image (shown as an overlay) and the other for the live image. This picture is difficult to interpret because all of the dots from both documents are the same color. The dots for each documents can be separated by using an alternate overlay option. Press the Overlay button to display the menu, select Graphic Overlay --> Red/Blue Overlay --> Normal Colors. The image will now look like this:

The printer dots are now colorized -- blue dots are from the saved overlay image and red dots are from the live image. By colorizing the dots, it is easier to see if any dots are different and also to determine to which document a dot belongs.

Once the overlay image is loaded, it is easy to compare other pages by simply sliding them under the camera or microscope and manually aligning the dots with the overlay image.

In some cases it is preferred to manipulate the overlay file instead of moving the sample. Hold down the SHIFT KEY, click and hold the left mouse button, and drag the mouse to reposition the overlay. To rotate the overlay, hold down the "R" key, click and hold the left mouse button, and drag the mouse left-right. Hold down the SHIFT or "R" key and double-click the left mouse button to return the overlay to the corresponding default position or rotation.