Lesson 5 Videos:
- Calibration for Illunis and Redlake Cameras Part 1
- Calibration for Illunis and Redlake Cameras Part 2
Introduction
See the DCam User Guide section titled “Grayscale Camera Calibration (Illunis, Redlake)” for more detailed instructions for Illunis and Redlake cameras.
In this lesson, you will learn how to calibrate your camera to capture the highest quality images. Calibration is the key to capturing high quality images, making it one of the most important skills you will learn for capturing historical records.
The processes in this lesson apply to both Illunis and Redlake cameras. When the camera has been plugged in to the computer and the DCam program has started, the software automatically identifies which camera is being used.
You decide when recalibration is needed. At a minimum, the camera should be calibrated at the following times:
- Each day when you are ready to start capturing images
- When the camera height has changed
- When the height of the copy board has changed
- When the lighting has changed
- If you change the type of document you are capturing, such as changing from a single page to a book
- After lunch or another long break
The device calibration tab in the footer bar shows if the camera has already been calibrated. Even if this tab shows that the camera has been calibrated, you may need to recalibrate the camera for any of the reasons noted above.
Both Illunis and Redlake cameras require the following calibration processes:
- Focus calibration
- White board calibration
- Exposure calibration
- Focus calibration for LSI
- LSI calibration
Getting to the calibration screen depends on whether you are practicing calibration or actually capturing images. If you are simply practicing, from the home page, select Practice Configuring Imaging Device. At the bottom of the left control panel, click Calibrate.
If you are getting ready to capture images, first create a new folder as described in the lesson “Projects, Listings, and Folders.” From the bottom of the folder screen, select Save and Capture.
Focus Calibration
To perform focus calibration, complete the following:
Step 1: Remove the document, and place the focusing target on the capture board.
Step 2: Click Start or Reset.
Step 3: If you are going to capture a folder, find the largest document, and place it directly beneath the camera lens. If you are going to capture a book, open it up, and place it directly beneath the camera lens.
Step 4: Adjust the camera height to the level to where you can capture the whole document, including a border of black copy board around it. The border should be at least several inches. If the whole document with its border cannot be viewed completely, move the diving board and attached camera higher on the center post of the workstation. If the whole document and its border does not fill the viewing area, move the camera down.
Note: After each adjustment, continue to click Refresh Image that so you can see your progress.
Note: A best practice is that the camera should never be closer than 22 inches (about 56 centimeters) from the copy board.
Step 5: If a document in a folder is larger than the camera can capture at the highest camera position, set the camera height to capture the size of most of the documents, and capture the large page separately.
Step 6: Manually focus the camera lens by turning the lens either clockwise or counterclockwise until the green column and focus score raise as high as possible.
Note: The green number has no significance except as a point of reference. It is not a measurement in an absolute sense.
Note: Turn the lens a small amount, and then stop and let the system think. Repeat the process. If the camera lens is continuously moving, the system may sometimes lock up and not focus.
Step 7: To check the focus, find the 1.0 lines on the focus card.
Step 8: Using the mouse scroll wheel, zoom to 2,300%, and position the screen to see the 1.0 vertical and horizontal lines on the focus card.
Rotate the scroll wheel away from you to make the pixels larger. Rotate the scroll wheel toward you to make the pixels smaller.
If the lines on the card are horizontal and vertical, the edges should be crisp with no more than 2 transitional pixels on either side of the fully blocked, or darkest, pixels. The darkest pixels are called fully blocked pixels. They may have a slight variance in darkness due to the ink of the target. The transitional pixels are pixels that are transitioning from the darkest black to the lightest background.
Step 9: Make minor adjustments to the camera lens as needed until the maximum focus score is achieved with no more than 2 transitional pixels on either side of the fully blocked pixels.
Step 10: Once the target is focused, click Next to calibrate focus.
A camera becomes out of focus when an image lies outside of the depth of field that the camera is adjusted to capture. Being out of focus usually occurs in the same location, image after image.
Generally, when the lens is set at F-8, a depth of about 1/2 inch will be in focus. This is important to know when you are capturing a book. Putting wedges under the front and back covers to keep the pages level can help keep the entire surface of the book in focus. For a thick book, however, you may need to refocus the lens at times, since turning the pages stacks them on one side. This means that one side of the book can end up higher and the other side can end up lower than the depth of field.
Step 11: To set the focus on a book, open it to a middle page before placing the calibration tools like the grayscale or the focus card.
Camera F-stops affect the depth of field. At times it might be necessary to change the camera F-stop. Smaller numbers, such as F-2 and F-4, have less depth of field. Larger numbers, such as F-11 and F-16, have a greater depth of field.
Note: Do not change the setting from F-8 unless you are directed to do so.
White Board Calibration
To calibrate white board settings, use a large, white foam-core board. Calibrating the white board ensures that lighting is evenly distributed across the entire capture area and dark areas are adjusted to give an even, balanced background. Calibrate the white board by completing the following:
Step 1: Remove the focus target used during focus calibration.
Step 2: Ensure the white board is free of dust spots, dents, smudges, static, blemishes, or dark marks of any kind by using a damp cloth or light sanding until the white board appears uniformly white.
Note: Anything dark on the board will appear in a bright white halo effect on every captured image. If the white board is damaged, order a new one.
Step 3: Place the large white foam-core board on the copy board with the dull side up.
Note: The white board must cover the entire viewing area. While the camera is adjusting, the message “Adjusting shutter” displays. The Next button is disabled.
Step 4: The white board should show an even green or yellow-green color across the viewing area.
Note: DCam displays warning messages that explain any problems.
Step 5: The colors in the DCam viewing area represent various light conditions.
If you see mostly green, it indicates that the amount of light is correct. If you see mostly yellow, then orange hot spots, it means there is too much light. Red indicates very hot spots, which indicate far too much light.
If you see light blue, then dark blue spots, it indicates cold spots, which appear because of too little light. It is normal to see colder colors in the corners and warmer colors in the center of the copy board. Once calibrated, however, the white board should never show any dark blue or red areas.
Step 6: The shutter adjusts to find the optimum center for the available light. If white board calibration is successful, the message “White board good” is displayed.
Step 7: Click Next.
Note: Do not remove the white board until after you click Next and the screen turns white.
Step 8: If the white board calibration is not successful, correct any problems. For more information, see the DCam User Guide sections titled “Calibrating the Lighting with a White Board” and “Troubleshooting Whiteboard Calibration.”
Exposure Calibration
Exposure calibration adjusts the tonal range of an image using a grayscale card. A grayscale card displays 255 values from the brightest white to the darkest black.
To calibrate these values, DCam identifies sections, or patches, of the card as A, M, and B. The software then ensures that all values fall between 23 and 242. If values fall outside this tonal range, information on the documents being captured can be lost. This loss is due to the over- or under-exposure of pixels, which results in the elimination of those pixels. This elimination of tonal data is called clipping.
Complete the following to calibrate exposure:
Step 1: Place the grayscale card on the copy board vertically in the center of the viewing area so that light can wash over it evenly.
Step 2: If you are capturing a book, open the book to the center pages with wedges under the front and back covers to make the pages as level as possible.
Step 3: Place the grayscale card on top of the book.
Note: Do not touch the surface of grayscale cards with your fingers. The oil from your skin can affect how color, light, and shadows are interpreted by the software.
Step 4: Verify that the radio button Automatically locate grayscale card is selected.
Step 5: Check the autofocus during calibration.
Step 6: The type of card being used should be shown in the top of the Calibration panel.
Step 7: If the card being used is not displayed, click Choose a different card.
Step 8: Select the correct card from the options, and click OK.
Note: DCam automatically locates the grayscale card patches. When the grayscale patches are found, the camera’s exposure and other settings are established.
There are situations where it is necessary to locate the grayscale card patches manually. Troubleshoot the following:
- Check that the card is correct and that it is centered.
- Check the lighting for extra glare or darkness. You might adjust the room’s or the workstation’s lighting.
- Remove excess clutter from the copy board.
- Make sure the camera F-stop is set at F-8.
If DCam still has trouble locating the grayscale card, you will need to manually locate the grayscale patches by following these steps:
Step 1: On the exposure screen, click Manually Locate Grayscale Patches. The 3 sampler targets and labels display.
Step 2: With the mouse, click and drag the targets onto their associated grayscale patches.
Step 3: The sampling tool displays orange when the pixel values are inconsistent.
Example: When placed partially between 2 patches, the sampler will have an inconsistent value. For that reason, make sure the sampler is correctly positioned.
Step 4: Click Start.
Note: The camera takes several snapshots, so make sure not to move the grayscale card. Red boxes appear on the screen around the A, M, and B patches on the grayscale card.
Step 5: If exposure calibration fails, one of the following problems may be the cause:
- If DCam cannot identify the A, M, and B patches on the card during calibration, you are reminded to ensure that the correct grayscale card has been selected.
- If a bad sample is indicated, check the grayscale card for damage.
- If the relative position of the samplers do not appear to be correct, DCam will display the following warning prompt:
- The sampler values should follow the rule: A > M > B
This statement means white is larger than gray, which is larger than black. If the sampler readings do not meet this rule, DCam will display a warning prompt.
Step 6: If the exposure calibration is successful, a green circle with a check mark appears with the text “Grayscale passes.”
After grayscale calibration is completed, check the adjusted grayscale values. The values should be in the following ranges:
- A-patch, White: 243 or less
- M-patch, Gray: 104-108
- B-patch, Black: greater than 23
Step 7: If the grayscale calibration does not pass, or if the values are not correct, adjust the lighting, and start the calibration over again.
Step 8: If you are working with documents that are whiter than the A patch of the grayscale card, click the Use Bright White Sampler check box.
Step 9: Place a bright white document onto the copy board next to the grayscale card, and then click and drag the Bright White sampler target onto the document.
Note: The Calibration Panel also displays the DPI (dots per inch or pixels per inch). The software uses the known size of the grayscale card to determine what DPI is being captured. This value is stored with every captured image.
Step 10: DPI changes with the height of the camera. It can be increased by lowering the camera or decreased by raising the camera. Some archives require that images be captured with a minimum DPI.
Note: If you are continuing to capture images for a folder that was already started, the LSI check dialog displays.
Step 11: If the camera height has not changed since the previous LSI was performed, continue with LSI focus and calibration by clicking Yes.
Note: If you click No, the capture images screen displays, and calibration is complete.
Step 12: If the grayscale calibration does not pass, or if the values are not correct, adjust the lighting, and start the grayscale calibration over again.
Focus Calibration for LSI
The LSI check ensures that the digital image shows even the finest lines of information as shown in the original document. This allows for the best legible preservation image possible.
When you originally focused the camera, if you did not place the largest document or book on the copy board to adjust the camera height and maximize the camera array, you are given a second opportunity to do so at this point in the calibration process.
If you are capturing a book, open the book to the center pages with wedges under the front and back covers to make the pages as level as possible. Place the white board and focus target on top of the book.
If you followed the correct process and adjusted the camera to the appropriate height prior to beginning calibration, you can click next to go to LSI calibration.
LSI Calibration
To make sure the handwriting or typing is about the same throughout, look through a few pages of the folder, and find a thin representative of the text. The text you choose can be either handwriting or type as long as it is thin, not faded, and not damaged. Most importantly, it must be representative of the thin text to be found in the collection. Complete the following steps to perform LSI calibration:
Step 1: If you are capturing a book, open it, and find the thinnest representative lines you can, as close to the center pages as possible. Do not select an embellishment, a finishing flourish on a character, preprinted lines, or lines on a governmental seal.
Step 2: Place the document you have chosen on the copy board.
Step 3: Click Next. A green selection box displays with an LSI area tool dialog box.
Note: Notice that because the entire document and the copy board are within the selected green box, your LSI score and check mark are green.
Step 4: Drag the corners of the green selection box to reduce its size so that it highlights only the thin representative text you chose.
Step 5: Once the thin text is highlighted with the green box, the LSI score will correctly show for the values of the chosen text.
Note: If at any time you want to start the selection process over again, on the LSI area tool dialog, click the Reset original area button.
The goal is to have an acceptable LSI score of 80 or above. However, a marginal score is acceptable. An LSI score of 90 or above is preferential.
Step 6: Click Next. If the LSI score is 80 to 89—this is considered marginal, but acceptable.
Step 7: Click Next. If the LSI score is 79 and below, it is an unacceptable LSI.
See the DCam User Guide section titled “Troubleshooting LSI Calibration” for more information on troubleshooting.
Step 8: Once there is an acceptable LSI score, a green circle with a check appears.
Step 9: Click Next. DCam indicates that the score has been saved.
Step 10: To capture images, click Next.
Learning Experiences
Activity 1: Check Your Understanding
- Both Illunis and Redlake cameras require what calibration processes?
- Both the Illunis and Redlake cameras only take grayscale images.
- True
- False