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8. Make sure TIFF Correction Mode is selected in the upper right corner and the TIFF Corrections tab is selected in the bottom right corner (Figure 44).
There are four main areas in this window:
- Left Exposure Interval panel:
- Line Trigger Interval: Interval that sets the Max Image Scan Speed. The target Max Image Scan speed is 8.33 cm/sec. Adjust the Line Trigger Values to achieve 8.33 cm/sec
- Red Exposure Interval: Sets the red exposure level
- Green Exposure Interval: Sets the green exposure level
- Blue Exposure Level: Sets the blue exposure level
- Left Histogram Graph: Displays histograms of the red, green, and blue curves
- Right RGB Values panel: Displays current absolute R, G, and B values of the image and the current image
- Right Profile Graph: Displays the profile curve of the RGB values
4. Place a flat (not bowed), clean gray scale card (standard) and place under the lights/camera. Be careful on how long you leave the card under the lights. The intense lights can damage it.
5. Look at the Red, green, and blue values in the right corner. If using a 50% grayscale card the red, green, and blue values should be approximately 127. The 'red/green' and 'blue/green' ratios should be approximately 1. If the values are off adjust the exposure levels in the left exposure interval panel and this changes the value of the pixel in the right hand panel. To make changes:
- Click the Green Lock arrow so it displays 'Off'. Now the Red and Blue Exposure Intervals will no longer be grayed out.
- Place the cursor in the white box displaying the Red Exposure value. Use arrow keys on the keyboard or type in values to adjust exposure values. While adjusting the exposure watch the red pixel value in the right panel. Adjust the exposure until the pixel value is 127.
- Repeat step b for green and blue values
You will notice the histogram and profile graphs roughly overlay one another.
6. Select the Lights tab (Figure 23). Select Lights OFF All Banks. The lights will now turn off
Figure 23. Lights information window
7. Select the Gains-Black-Shade-Flat tab (Figure 24).
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Figure 44: Tiff correction Mode button and Tiff Correction tab both highlighted in red.
9. Open the tiff image just taken (Figures 45, 46).
Figure 45: Open Test Image Window with all images displayed.
Figure 46: The tiff image loaded into the Original Window.
10. In the ORIGINAL image control create a selection rectangle (right-click drag) of the MacBeth card and click CROP (Figure 47). Repeat as necessary until the card fills the entire image.
Figure 47: Green crop square drawn around the color squares.
11. Again create another selection rectangle over the image but do not release the mouse. Move the lower corner of the rectangle until small white boxes appear over the color squares. Make sure the boxes are in the center of the squares. Release the mouse. The pixels in the squares will be averaged and used for the RGB values in the calibration (Figure 48). (not quite how it works right now, white squares don't show up until mouse is released, error reported in confluence)
Figure 48: Final crop square drawn around color squares.
12. Look in the TIFF Correction tab and set the LUT polynomial order values for the RGB channels. Adjust these values to create the lowest residual error with the smoothest curve in the UNCORRECTED image tab. Should be around 4. Make sure that the curve does not wave about if it does the order values need to be lowered. Also check the corrected ROI and MacBeth values should be very close. Make sure that the white does not exceed the MacBeth value. If you are unable to produce a reasonable correction curve, it may be necessary to redo your white balance correction and start over.
This correction is applied to both the TIFF and JPEG image but for the JPEG image you can also apply a Brightness, Contrast and Gamma correction. This is done at the photographer’s discretion. With better balanced leds on the new light system I did not use the correction and left the values at their mid-points.
Camera Height Adjustment
- Move the camera so it is just on the edge of the grayscale card at the end on the tray. On this card are mm and cm marks on the edge.
- Click the GRAB button and watch the image as you make slow camera position adjustments until the centimeter lines show up on the image graph as sharp spikes.
- The graph as two cursors, use the mouse and drag one cursor aligning it with the spike. Take the second cursor and do the same with an adjacent spike. Just above the Profile graph there is a control labelled Pixel Delta this value should be between 198 and 202 pixels. If not, adjust the camera (not lights up and down refocusing after every move until you get within the range. Warning this can be very tedious!
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8. Click Pixel Black Auto Correction.
9. Go back to the Lights tab and select Lights on to Saved Levels (For the JAI Camera Setup, use 100% lights.)
10. Place the same grayscale card back underneath the lights as flat as possible. Tilt in the card changes the shape of the pixel value profile and shape/location of the histogram. It is important to use a flat grayscale card to accurately calibrate.
11. Defocus the lens of the camera manually. In the image grab window you will see the card grains go away and the image will become a smooth gray. This changes the profile graph from a relatively straight line to a bowl shape as shown in the camera manual (CV manual, page 12, 6.4.)
12. Then click Shading Correction - Flat Method - button. This corrects the bowl-shape to a flat line as seen in the pixel profile graph.
13. Now Click the Pixel Gain Correction – Flat Method – button
14. At this point check the red, green, and blue pixel values. If they have jumped around adjust the Master Gain Setting to get the values close to 127. When close to 127 click White Balance. The lines now completely overlap each other smoothly.
Check Against Macbeth Color Standard
Correcting the White Value
1.Place the Macbeth Color Standard on the track against the top edge. The standard should be flat and level in the track. The color values will change on the degree of tilt.
2. Next, physically move camera/lights over the color standard (Figure 25).
3. Use courser to draw rectangle around the white field in the field of view of the camera (top right window). The red, green, and blue pixel values reflect the values inside the rectangle. If no rectangle is drawn the values will reflect the entire image. In the lower right window, you will see the color lines. If the lines are angled (left to right or right to left), move the color standard to line it up in the holder. The lines might be drifted out of the window/field of view.
4. Click on the Charts tab (Figure 26). Click on a color box and the manufacturer provided red, green, and blue values will populate. This provides a way to compare expected values with measured values and allows the user to make additional adjustments.
5. Click in the white box to see what the values should be. Compare those values with the values recorded by the camera in the upper right window. If the values do not match there are two options to correct:
a. Option 1: Go to the Gains-Black-Shade-Flat tab. Adjust the Master Gain Value and watch the red, green, and blue pixel values in the upper right window.
b. Option 2: Go the Rates and Exposure tab. Adjust the exposure of the color(s) that are not correct until the value is approximately the same as the manufacturer value.
Either option is appropriate. Ideally not more gain than necessary is used
13. Use the “Chart” screen and click on white to see what the values should be. Then use the gain in the “Gains/Black/Shade/Flat screen” to slowly reduce the Master gain for “all gains”. When you do that, the color lines in the lower right window will drift back into the field of view. Just like before, you want to adjust the lines of green, red and blue to end up on top of each other by adjusting the values in the “Rates and Exposure” screen.
Correct the Black Value
1. Physically move camera/lights until you see the black square in the image grab window. Use cursor to draw rectangle around in the black box.
2. Go back to the Charts tab. Click in the black color square and compare the manufacturer red, green, and blue values with the measured values. If the values do not match go to Gains-Black-Shade-Flat tab. The target red, green, and blue value are different than the manufacturer values. If adjusted to the manufacturer values the core images tend to be too dark. For this reason we aim for red, green, and blue values of 15.
3. In the Gains-Black-Shade-Flat tab adjust the Master Black value until the pixel values in the upper right window are approximately 15.
4. When you are done with the black gain, check the white gain again. Move the camera so it is over the white square in the Macbeth Color Standard and draw a rectangle in the white square.
5. In the Charts tab click in the white color box. Compare the manufacturer values with the measured values from the camera. If the values do not match follow one of the two methods explained in Step 5 of Correcting the White Value
6. Click Save in the bottom right corner
TIFF Image Corrections
Setting up for Image Capture
1.With a target underneath the camera, manually refocus the camera lens.
2. In the main IMS Panel select Motion > Drive Enable to re-enable the motor (Figure 27).
3. Go to IMS Main Panel Select DAQ > Image Capture Setup (Figure 28). In this window confirm that speed is set lower than the speed calculated by the Line Trigger Interval (typically 8.33 cm/sec). Current speed setting is 7.0 cm/sec
Take an Image
1. In the IMS Main Panel click Start and the Sample Information Window will open (Figure 29)
2. Put cursor in the 'Scan' box and scan the STND COLOR and LIG label posted on the track above the desk (Figure 30).
Figure 30. Standard label to scan MacBeth Color Checker
3. Check the ColorChecker Standard box in the lower left corner (Figure 31). This produces a raw TIFF image without corrections applied.
4. Click Take A Picture in the lower right corner. The lights will turn and image the standard.
5. Adjust the green crop box the image to include all the ColorChecker color squares (Figure 32).
6. When satisfied with the crop box click Crop Image and then the green Save button. A new Sample Information window will pop up. Click Cancel to close out of the window.
Image Correction
1. In the IMS Main Panel go to Instruments > CAMERA: IMAGE Correction (Figure 33)
2. The main Image Correction Window opens (Figure 34). Make sure, TIFF correction is selected. Always select and process TIFF before JPEG.
The Image Correction Window allows users to compare a test image of the standard with known values of the standards. There are three main areas in the window:
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- Uncorrected Tab: Shows the measured Red, green, and blue values of the gray scale color squares.
- Applied Corrections Tab: Applies polynomial fit corrections to the RGB lines.
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- Original
- Corrected
- Color Checker
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2. Click Open Test Image and navigate to the ColorChecker Standard Image just taken. Select the TIFF file (Figure 35).
3. The entire image will load into the Original and Corrected panel but for this application we only need the color squares. Click on the square tool next to the Original panel and draw a box around the color squares in the image (Figure 36).
4. Click Crop. Now just the color squares are seen in the Original Panel. The new cropped image will also update in the Corrected panel.
5. With the 'Square' tool still selected draw another, tighter box around the image and click Crop
6. With the 'Square' Tool draw another box but this time you will see white tick mark boxes over the colored boxes. Adjust the box so the white tick marks are in the center of the squares. The white box should always be in the top left, make sure the color checker is not in the holder upside down.
7. Now we will be using the gray-scale color squares, outlined in red below, to check and compare RGB values (Figure 37). The goal is to get the corrected image grey scale RGB values as close as possible to the ColorChecker Manufacturer gray scale RGB values.
Figure 37. Gray scale color squares in Color Checker box
8. In the BCG Correction Window select the TIFF Correction tab (Figure 38). In the large graph window on the left select the Uncorrected Image tab.
- RED Poly / R residue:
- GRN Poly / G residue:
- BLU Poly / B residue:
9. Try to get the residuals low (the smaller the better), while having a curve fits good as possible (see bad example, good example).
10. In order to line up the TIFF – JPEG Image correction, the end members of white and black cannot be at the extremes (250, 0), otherwise the correction will not be able work.
11. Once the grey/white/black are fitted as close as possible, check that the screen “applied corrections” shows a good linear fit.
12. Then check all the other colors for applied corrections.
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Check on Calibrated Computer
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