Dcam User Guide-Color Calibration (Nikon)

Sections:

About Camera Calibration
When to Calibrate
Preparing for Camera Calibration
Setting Camera Height
Single Step Calibration
Multistep (Manual) Calibration
Calibrating Exposure
Calibrating White Balance
Calibrating Focus
Capturing the Color Target
Troubleshooting Calibration

About Camera Calibration

Calibration is a process to establish the correct camera settings for capturing high quality images. There are 2 sets of calibration steps: 1 set for color cameras and 1 set for grayscale cameras. When the camera is plugged into the computer, DCam automatically identifies which camera is attached.

Note: Keep the camera well-calibrated. Calibration is the key to capturing good quality images.

When to Calibrate

The device calibration tab in the footer shows if the camera has already been calibrated. However, if the camera environment has changed, even if this tab shows that the camera has been calibrated, you may need to recalibrate.

At a minimum, the camera should be calibrated under the following circumstances.

• Each day as you start to capture images.
• If any of the following have changed:
  
  • Camera height
  • Capture board height
  • Lighting
  • Change in type of document, such as transitioning from a single page to a book
• After lunch or a long break.
• Every time you create a new folder if the lighting or height of the camera is changed.
  

Preparing for Camera Calibration

To prepare for camera calibration, follow these steps:

Step 1: Turn on workstation lights.

Step 2: If possible, eliminate other light sources, including light from windows, doors, or other lighting systems.

Note: Recalibrate the camera any time there is a change in lighting.

Step 3: Verify that the camera and stand are set up on a hard, sturdy surface, such as a solid desk or table.

Step 4: Use the bubble level to verify that the table, copyboard, and camera-stand surfaces are parallel and level. This keeps the entire capturing field in focus once the camera is calibrated. Level these surfaces in the following order.

• Table
• Copyboard
• Camera stand

Step 5: Remove the camera lens cap.

Step 6: Turn on the computer.

Step 7: Turn on the camera.

Step 8: To start the application, on the computer’s desktop, double-click the DCam icon.

Step 9: Verify that the correct camera is selected by looking at the current device designation in the bottom-right section of the home screen. If the correct camera is not selected, select the correct one in preferences.

Step 10: In the folder, find the largest document to be captured in the folder

Step 11: Ensure that the camera is set to a height that will maximize the capture of the document.

Step 12: Create folders in the folders section of the Manage Projects, Listings, and Folders screen.

Setting Camera Height

Camera height should be set in relation to the largest document in the folder. Ensure that the entire document can be viewed. Additionally, establish a camera height that allows for the capture of many document sizes. The best practice is to keep the camera height at 22 inches (56 centimeters) or higher from the copyboard.

Step 1: Click Manage Projects, Listings, and Folders.

Step 2: Identify the correct listing, and create the required folder. (See Creating a New Folder)

Step 3: At the bottom of the folder screen, click Save and Capture. This starts the calibration steps.

Step 4: Place an open book or the largest document from the folder on the copyboard under the camera lens, and click Refresh Image. The image displays on the screen.

Step 5: Adjust the camera height, and continue to click refresh image until you get the camera at the correct height.

• If the whole document page cannot be viewed, then move the camera up. If the document does not fill the viewing area, then move the camera down.
• If a document is larger than the camera can capture at the highest position, set the camera height for most of the page sizes and capture the large page separately. (See Capturing a Large Document.)
• A best practice is to keep the camera height at 22 inches (or 56 centimeters) or higher from the copyboard in most cases.
• A thin black border that is ½ inch to 1-inch wide (1.2 to 2.5 centimeters) should run around all 4 sides of the document.

Step 6: Click Continue with Calibration. (See Calibrating Exposure.)

Single-Step Calibration

As the name implies, single-step calibration performs camera calibration in 1 step.

Step 1: In preferences, verify that single-step calibration is selected. It is the default setting.

Step 2: Place the grayscale, color, and focus calibration targets on the copyboard. Make sure the targets are completely within the camera’s view. The target you use must match the targets pictured in the left panel of your screen under current reference target.

• With your other workstation equipment, you may have a protective plastic case, known as a “clamshell.” It includes all of these targets in one unit.
• If you do not have a clamshell, place the individual targets on the capture surface. As long as they can be seen by the camera, their placement does not matter.

• If the physical targets you have with your workstation equipment do not match the target that is pictured in the left panel, under current reference target, you need to designate which targets you will be using so that the screen matches your physical targets.
• To change the targets, click Choose a different reference target. A dialog displays.
• Choose the button that corresponds to the target set you want to change. A dialog displays that allows you to specify the physical target you have.
• Select the correct target.

Step 3: To begin single-step calibration, click Start. DCam goes through the following calibration steps automatically.

• Focus
• Locate targets
• Exposure adjustment
• White balance adjustment
• Color target capture (tone curve adjustment)

The first time you run calibration, the process can take up to 1 minute. Subsequent calibrations take less time, sometimes as few as 10 seconds, depending on how long it has been since the last calibration and how dramatically lighting conditions have changed.
Step 4: When these processes are complete, click Next.

Step 5: To verify that the focus meets quality standards, do the following:

• Use the mouse’s scroll wheel to zoom to 2,300%.

Note: To make the pixels zoom bigger, rotate the wheel away from you. To make the pixels zoom smaller, rotate the wheel toward you.

• Position the screen to view the “1.0” vertical and horizontal lines on the focus card. 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 (darkest) pixels.

Step 6: To troubleshoot any problems that may arise, check the following:

• From your view on the screen, verify that the targets on the copyboard are within the camera’s view.
• Verify that the correct grayscale and color targets are selected in DCam.
• Complete the multistep (manual) calibration steps in the next section.

Multistep (Manual) Calibration

Multistep (manual) calibration takes you through each of the calibration steps manually. This can be helpful especially if single-step calibration fails in some way.

Step 1: In preferences, verify that single-step calibration is not selected. (Single-step calibration is the default setting.)

Step 2: Click Manage Projects, Listings, and Folders.

Step 3: Identify the listing you want, and then create a folder. See Creating a New Folder.

Step 4: To start the calibration process, at the bottom of the folder screen, click Save and Capture.

Calibrating Exposure

Exposure calibration measures the tonal range of an image by comparing a standard set of gray tones that are stored within DCam against the shades of gray in a grayscale card you have placed on the copyboard. This card consists of 255 values, from the brightest white to the darkest black.

To calibrate these values, Dcam identifies certain patches of the grayscale card, (which are marked as A, M, and B). It then ensures that all values on the card fall between the measurements of 23 and 242 (out of a possible range between 0 and 255). If values fall outside these measurements, tonal information that creates different shades of gray on the records you capture can be lost because of a light-exposure error. This type of error is known as “clipping” because those tones are “clipped off” when viewed in a digital tool called a histogram. (See Understanding Capture Problems.)

Step 1: Place the grayscale card vertically on the copyboard in the center of the viewing area so that light can wash across it evenly.

• If you are capturing a book, open it to the center pages with wedges under the front and back covers to make it as level as possible, and then place the grayscale card or clamshell (the plastic case with color and shade targets within it) on top of the book.
• If the grayscale card is curled, worn, or dirty, replace it.

Note: Do not touch the surface of the grayscale card with your fingers. The oil from your fingers can affect the card grayscale values over time.

Step 2: Verify that the radio button Automatically Locate Grayscale Card is selected.

Step 3: Check Autofocus during calibration.

Step 4: The type of card being used should be displayed at the top of the calibration panel. If not, click Choose a different card.

Step 5: Select the correct card from the available options and click OK.

Step 6: DCam automatically locates the grayscale card patches. When they are found, it establishes the camera’s exposure and other settings.

Step 7: There are situations when it is necessary to manually locate the grayscale card patches: DCam cannot always automatically locate the grayscale card because some documents are whiter than the A-patch on the grayscale card, or there is not enough light to automatically identify the grayscale card. If DCam has difficulty automatically locating the grayscale card, check the following:

• Make sure you selected the correct grayscale card.
• Remove excess clutter on the copyboard surface and retry.
• Make sure the grayscale card is centered.
• Move the grayscale card to different positions or slightly different angles, and retry.
• Move lights to provide more light to the copyboard.

Step 8: If DCam still has trouble locating the grayscale card, manually locate the grayscale patches by following the next steps. Otherwise, skip to step 9.

• On the exposure screen, click Manually Locate Grayscale Patches. The 3 sampler targets and labels display.
• With your mouse, click and drag the targets onto the grayscale patches, as directed. The sampling tool displays orange when the pixel values are inconsistent. For example, when placed partially between 2 patches, the sampler will have an inconsistent value. Make sure the sampler is correctly positioned.

Step 9: Click Start. The camera takes several quick shots, so make sure not to move the grayscale card. On your computer screen, red boxes appear around the A, M, and B patches of the grayscale card.

• If, during calibration, DCam cannot identify the A, M, and B patches, a message reminds you to ensure that you have selected the correct grayscale card.
• If DCam indicates a bad sample, check the grayscale card for damage.
• If the relative position of the samplers do not appear correct, DCam displays a warning prompt.
• The sampler values should follow the rule: A is greater than M, which is greater than B, (A > M > B), which could be restated: white is greater than gray, which is greater than black.

Step 10: If the exposure calibration is successful, a green circle with a checkmark displays with the text grayscale passes.

Step 11: When complete, check the adjusted grayscale values. They should be in the following ranges:

• A- (White): 243 or less
• M- (Gray): between 104 and 108
• B- (Black): greater than 23

Step 12: During grayscale calibration, DCam measures the DPI (dots per inch or pixels). DPI increases the closer the camera is to the copyboard. If the grayscale calibration does not pass, or if the values are not correct, adjust the lighting, and start the calibration over again. Some archives may require images to be captured with a minimum DPI.

Step 13: Click Next.

Calibrating White Balance

During white balance calibration, a white piece of paper provides DCam with a reference point for the shade or color white.

Step 1: Remove the grayscale card you used during exposure calibration.

Step 2: Place a clean white piece of paper on the copyboard.

Step 3: Click Start. When white balance has been calibrated, the next button briefly flashes.

Step 4: Click Next.

Calibrating Focus

Calibrating focus produces sharp, crisp lines in text and writing.

Step 1: Place the largest document in the folder on the copyboard. If capturing a book, open the book to a center page, and place wedges under the front and back covers to make it as level as possible.

Note: If the document does not display on the screen, check that the lens cap has been removed from the camera and that the camera is being recognized.

Step 2: Manually adjust the camera height so the entire document can be seen in the screen’s capture frame. It should fill as much of the frame as possible, leaving a black border along all 4 sides of the document or book. If needed, turn the document so that it fits in the frame with the longest side of the document running along the longest side of the camera frame. The best practice is to keep the camera height at 22 inches (56 centimeters) or higher from the copyboard.

Step 3: Place the focusing target on the copyboard board. Do not allow any object in the viewing area while the camera is being focused.

Step 4: Click Autofocus.

Step 5: To begin checking the camera’s focus, find the lines next to 1.0 on the focus card, and position them on the copyboard near the center of viewing field.

Step 6: Using your mouse’s scroll wheel, zoom to 2,300%. Position the image on the screen to clearly see the 1.0 vertical and horizontal lines. The darkest pixels are called fully blocked pixels. The pixels that transition from the blocked pixels to the light background are transitional pixels.

Step 7: When you have positioned the lines on the card so that they are horizontal and vertical, the edges should be crisp with no more than 2 transitional pixels on either side of the fully blocked pixels.

Note: Rotate the wheel away from you to zoom the pixels larger. Rotate the wheel toward you to zoom the pixels smaller.

Step 8: If you need to, manually adjust the camera’s focus by using the arrow buttons under manual focus in the left control panel. Continue adjustment until you achieve the maximum focus score with no more than 2 transitional pixels on either side of the fully blocked lines.

• When using the manual focus controls, first adjust to the left until slightly out of focus, and then adjust to the right until the best focus is achieved, which displays as the maximum green and highest score.
• To make slight focus adjustments, click the left and right single arrow buttons.
• To make greater focus adjustments, click the left and right double or triple arrow buttons.

Note: When calibrating the camera to capture a book, perform all calibration steps on the top of the book.
Step 9: Once the target is focused, click Next.

Capturing the Color Target

To capture the color target, follow these steps:

Step 1: Place the color target so that it is centered in the viewing area.

• If DCam locates the target, a green rectangle displays around the color target. Click Next.
• If the color target is not recognized, make sure it is placed directly under the camera, and start the color capture over again.

Note: If you are capturing a book, open it to the center pages with wedges under the front and back covers. This makes the book as level as possible. Then place the color clamshell or the targets on top of the book.

Troubleshooting Calibration

If you are working with documents that are whiter than the A patch of the grayscale card, check the Bright White Sampler check box. DCam uses the bright white sample area instead of the A patch for calibration.

Place a bright white document onto the copyboard next to the grayscale card, and then click and drag the Bright White sampler target onto the document.

Troubleshooting Whiteboard Calibration

You may encounter several common problems with Whiteboard Calibration.

• Bright white halo shapes on images can indicate dust, spots, dents, or other imperfections with the foam-core board. Ensure the whiteboard is free of dust, spots, dents, smudges, or anything else. Additionally, if there are dust spots or hairs on the camera lens, they can show faintly in the background on every captured image.

Note: Use tools to zoom in on a problem area to inspect more closely.

• A common problem occurs when the whiteboard is placed on the copyboard at a skewed angle, leaving one corner dark.
• An item left on the whiteboard can trigger 3 warnings in the left panel.
• Sometimes it is difficult to get even lighting. Be aware of light coming from windows because it changes throughout the day as the sun moves. Also be aware of overhead lights that automatically turn on and off because of movement sensors.
• Whiteboard calibration detects hot spots and cool spots in the lighting distribution and tries to compensate so that the lighting is even. If, however, the system is unable to calibrate the whiteboard, DCam will display an error message. To fix the problem, use the tables below, and address environmental lighting sources. Adjust the light bars in the control panel for more or less light. Below are some examples of lighting problems.

Problem	Example
Whiteboard with red means too much light
Whiteboard with red spot may point to area of bright light reflection
Whiteboard with red section may mean too much light in one area
Whiteboard with blue may mean not enough light is available

The table below suggests solutions for correcting hot and cold spots.