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Automatic Mosaicking & Mosaic Tool

PCI Geomatics -

The purpose of this tutorial is to highlight Geomatica’s advanced automated mosaicking capability. The primary mosaicking operations that will be exposed in this tutorial are image normalization, cutline editing and image color balancing. New color balancing tools have been added in Geomatica which are outlined in the color balancing section of this tutorial.

 

Project Setup

  1. Open the OrthoEngine application
  2. In the OrthoEngine menu bar, click File > New
  3. Give your project a Filename, Name and Description
  • Select None (mosaic only) as the Math Modeling Method
  • Click OK
  1. Input the appropriate Output projection and Resolution for the project

  1. Click OK

 

Adding Images to the Project

  1. In OrthoEngine, change the Processing step to Image Input
  2. Click on Open new or existing image button

 

  1. In the Open Image panel, click New Image
  2. In the File Selector navigate to the images you want to input
  3. Click OK to the pop up message

  1. Click Close

 

Define Mosaic

  1. In OrthoEngine select the Display Project Overview button

  1. The Project Overview window opens to display all of the images in the project.

  1. Close this panel
  2. In OrthoEngine, change the Processing step to Mosaic
  3. Click the Define Mosaic Area button

  1. In the Define Mosaic Area panel, click Browse
  2. In the File Selector, select the output file name and location for the mosaic fill
  3. Leave everything else as default in Define Mosaic Area Dialog box

Footprints

The Define Mosaic panel allows the user to define the mosaic file that will be used to hold the mosaicked imagery. In this panel, the user can:

  • Set which images to include in the mosaic, by selecting/unselecting the footprints
  • Set the mosaic bounds by dragging the red rectangular boundary extent
  • Specify, which channels to include and the bit-depth of the channels
  1. Click OK

 

Generate Mosaic

  1. In OrthoEngine, click the Automatic mosaicking button

  1. In the Automatic Mosaicking panel, change the Normalization method to Adaptive Filter by selecting it in the dropdown list and click Apply All

For optical imagery, the Adaptive Filter and Hotspot are the only 2 normalization methods that are relevant.

  1. Under Mosaicking Options, ensure Bundle method is selected. This option must be selected in order to use the new color balancing tools.
  2. Leave the Cutline options as their defaults

  1. Under File Options, click Browse next to preview file and ensure this is saved to your desired directory.
  2. The panel should look like below:

  1. Click Generate Preview

Note:

Mosaic Preview and Generation

Generate Preview creates a low-resolution version of the mosaic. The preview file is saved under the path and file name specified in the Preview File box. You can use the preview of the mosaic to verify the color balance and cutline selection before continuing with the full resolution version. Click on Generate Mosaic and this will process all files and create the full-resolution version of the mosaic. The output mosaic is saved under the path and file name defined in the Define Mosaic window.

  1. The Progress Monitor opens

  1. The following preview will appear:

Note:

About the Preview

The preview mosaic is a very valuable output, because it is a low resolution preview of the final mosaic, which provides the user with a strong idea of how the automatic settings for the color balancing and cutlines will turn out. Preview takes a fraction of the time to generate as compared to the final full resolution mosaic, so different settings can be used in different runs to compare which parameter set will provide the best results.

  1. If you are satisfied with the results, you may click the Generate Mosaic button on the Automatic Mosaicking window to generate the full-size mosaic. If you are not satisfied, you may try different color balancing methods and run the Generate Preview

    *NEW COLOR BALANCING: If you are generally satisfied with the results, but see a few areas where the automatic color balancing was not correct, you can edit your full mosaic in the Manual Mosaicking tool. This will be covered in the Color Balancing step in this tutorial. Make sure you generate the full mosaic, using the Bundle color balancing method before you begin the color balancing edits.

 

Edit a Cutline

Once you have generated the mosaic using the Bundle option you can perform edits and additional color balancing by choosing the Manual Mosaic tool. Before you perform color balancing you should fix any cutline issues.

  1. Open the Manual Mosaicking tool from the Orthoengine toolbar.

  1. Your new mosaic will appear. If you expand the mosaic file you can see which images are included in the mosaic. If you would like to change the cutlines or perform color balancing on an image right-click the image and choose Reprocess.

  1. Select the image you chose to reprocess from the image tree list. Click the Collection View button
  2. The collection viewer opens and your working image is shown on top. Using the neighbors toggle button you can choose to display the neighboring image underneath.
  3. Zoom into one section of your image along the cutline that overlaps the neighboring image. You can experiment with blend width, contrast, brightness and visualization mode.
  4. To edit the cutline, click on the Vector Editing Toolbar iconThe Vector Editing Tools window opens. You must select the cutline using the find button in the vector editing toolbar. Once selected, the vector editing tools will be available.

  1. You can add vertices or move current vertices and reshape your cutlines. For instance you may wish to reshape cutlines that fall in a waterbody since these are likely to change color across the images. In the images below a cutline through a lake has been edited. You will also notice that the cutline clipping is enabled in the second image. This option allows the user to clip the working image to the cutline.

 

Color Balancing

Once you have edited the cutlines to minimize large color matching issues you can edit the color balancing for areas of poor matching. 

  1. In the Manual Mosaic window the color balancing toolbar will be available.

  1. Zoom to an area of the image where the images did not match well, such as the blue highlighted area above.

 

Edge Dodging Points

  1. Use the Select tool and select the left image. It will flash cyan to indicate that it has been selected. In the situation above the image on the right is darker and more blue than the image on the left. We will add edge dodging points and change the color and brightness of this area.
  2. Using the add edge point tool place three dodging points along the edge of the color change.

  1. Select all three points and open the dodging brightness slider

  1. You can adjust this slider to change the brightness of the image that you selected. You can also chose to only change specific bands by changing the channel selection from the color balancing editing settings

  1. Beside the dodging brightness buttons are the dodging contrast buttons. You can open the dodging contrast slider to change the contrast.

  1. You can also use the Automatch Edge Point tool to auto match the colour balancing on both sides or one side of the edge point.

 

  1. Use the Adjust Pair Point button to switch which side of the cutline (image) you are applying the dodging point edits to.

 

Floating Dodging Points

  1. Another type of dodging points is floating dodging points. You can use these points to fix local problems without affecting other areas of the image.
  2. On the toolbar, click on Floating Dodging Points button
  3. Right click to place a floating dodging point on a section of the image with poor color balancing.

  1. In order to prevent the color changes made to this point from spreading to the rest of the image, you can place other dodging points around the one you created.

  1. You can now select the middle point and adjust the brightness or contrast of that dodging point. You can add more dodging points or move the surrounding dodging points to allow for greater spread of the contrast and brightness adjustments.

 

Dodging Statistics

  1. Another method that you can use to adjust the color balancing of dodging points is the dodging statistics tools. With these tools you can copy the image statistics from one area and apply them to a different area using dodging points.
  2. In this example we will copy statistics from a different industrial area to improve the colour of this oversaturated industrial area.
  3. Place dodging points around the area that you wish to adjust.

  1. Using the Store Statistics tool select an area with the desired color balancing. You can choose to extract the statistics using a point, rectangle or polygon.
  2. Once you have the statistics stored, place a dodging point on the bright industrial area and then click Automatch to Statistics. You may need to click this a few times to produce the desired results. Once you Automatch you can also change the brightness and contrast to further improve the color.

  1. Make sure to save your project using File > Save on the OrthoEngine panel.

 

Reapply Mosaicking

In this step you will add your edits to your mosaic.

  1. Once you have made all the necessary edits to each of the reprocessed images you will need to add those edited images back into the mosaic. In order to do this you can reapply mosaicking. The cutlines and color balancing edits that you made will be applied but the original mosaicking order will be maintained.
  • Close the Manual Mosaic window and save your project.
  • On the OrthoEngine toolbar click the Reapply Mosaicking button

  • Click Generate Mosaic. You can now open your mosaic in focus to see the edits that were added

  1. Another way that you can save the edits to your mosaic is to right-click the image in the Manual Mosaicking window and choose Add to Mosaic. The image that you add will be added on top of the other images. You should only use Add to Mosaic if you wish to change the order of your mosaicked images.
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