Mosaic Tool

In image processing, mosaicking means to join several overlapping images to form a single, uniform image. It is similar to creating a jigsaw puzzle with your images, and then making the seams disappear. For the mosaic to look like a single image instead of a collage of images, it is important that the images fit together well.

More information on each of the steps that are run in this tutorial is included in the online Help Documentation for CATALYST Professional.

MOSAICKING FLOWCHART

The mosaicking flowchart below outlines different workflows for initializing a mosaic project, adding source images, defining the output mosaic file, applying mosaic preparation steps, editing the images and generating a mosaic in CATALYST Professional.

CATALYST PROFESSIONAL MOSAIC TOOL INTERFACE

The following figure identifies the basic elements you will work with in the CATALYST Professional Mosaic Tool window, including the Menu Bar, Toolbars, Control Pane, and View Pane. Please refer to this diagram when following the instructions of the tutorial.

For more information on the Mosaic Tool, click on the CATALYST Help button or search About the Mosaic Tool window in CATALYST Help.

Note: For large mosaic projects, you can work with a subset of the mosaic images by opening the project from the Mosaic Overview window (See Section 6.3).

1. MOSAIC PROJECT CREATION

When initially creating a mosaic project, the following criteria needs to be considered:

1. Is your data orthorectified?
2. Are you using a scripting environment or the CATALYST Professional graphical user interface?
   • For general information about running CATALYST functions in Python or EASI, including tutorials, videos, and tools, go to the Developer Zone.

1.1. PRE-ORTHORECTIFICATION

If your data is not yet orthorectified, you can start by orthorectifying your images. Your options for orthorectification are:

1. CATALYST OrthoEngine
   • Follow the Orthorectification tutorial for details on orthorectifiying your data using the CATALYST Professional graphical user interface.
   • Once orthorectification is complete, begin mosaicking from OrthoEngine. From the Processing Step dropdown, click Mosaicking. The Mosaic Tool opens and your ortho images will be automatically loaded into the New Project Wizard.
   • Go to Section 2.1.
2. Scripting
   • If you are running CATALYST functions in a scripting environment, use the ORTHO algorithm to orthorectify your data.
   • For information about the algorithm inputs and parameters, search ORTHO in the CATALYST Help.

1.2. POST-ORTHORECTIFICATION

If you have images that are orthorectified, they are ready to mosaic. Your options are:

1. CATALYST Mosaic Tool
   • Open the CATALYST Mosaic Tool directly from the CATALYST Professional Toolbar. Once it opens, click New Project to open the New Project Wizard.
   • Go to Section 2.
2. Scripting
   • If you are running CATALYST functions in a scripting environment, use the MOSPREP algorithm. MOSPREP creates reduced-resolution files, determines normalization coefficients, performs color balancing, and computes cutlines. The output is a mosaic project consisting of a source-image list file (.MOS) and a folder of all the information necessary to manipulate the images before adding them to the mosaic.
   • For information about the algorithm inputs and parameters, search MOSPREP in CATALYST Help.
   • Once MOSPREP has run, you can open the output .MOS file (or .PRJ and .XML files for Geomatica 2017 and earlier) in Mosaic Tool.
   • In Mosaic Tool, click File > Open Project. To edit the source images, proceed to Section 3.

2. MOSAIC PROJECT PREPARATION

Once your data is orthorectified, you can start preparing your mosaic project. New mosaic projects are created and defined using the New Project Wizard.

To open the New Project Wizard:

1. Open Mosaic Tool from the CATALYST Professional Toolbar.
   
2. The Mosaic Tool window opens. Go to File > New Project.
   
3. The New Project Wizard opens.
   

The following sections outline the steps of mosaic project creation in detail.

2.1. ADDING SOURCE IMAGES

Note: If you are opening the New Project Wizard from OrthoEngine, the images will already be loaded, so you can proceed to Step 3 below.

Your first step in creating your mosaic is to select the source images you want. Source images consist of the raster data you want to mosaic. Typically, source images for a mosaic are:

• overlapping,
• orthorectified, and
• fully cover the area of interest (AOI).

It is good practice to first review the images to determine which ones are best (e.g., open them in Focus).

To add source images to the mosaic:

1. On the New Project Wizard – Source Images window, select Open.
   
2. The File Selector window appears. Navigate to the folder containing the images you want to include, select the ones you want, and click Open.
   • For the tutorial, the six orthoed Hamilton_Airphoto_RGB.pix files are chosen.
     
3. The images are added to the project and displayed in the control pane under Source file list. For now, the images are represented in the view pane as overlapping footprints.
   
4. For Source NoData, enter a NoData value for the source images, if necessary.
   
   Note: Any NoData values you specify at this time will apply to all source images. If you want to set a NoData value or values for an individual image, or a group or range of images, you can do so in the Mosaic Tool window after you generate the mosaic preview. For more information, search Setting NoData values for source images in CATALYST Help.
   
   
   
5. Click Next.

The New Project Wizard – Mosaic Definition window opens.

2.2. DEFINING THE MOSAIC

After you add the source images you want to use, your next step is to enter definition information about the output mosaic file.

To define the mosaic:

1. The New Project Wizard – Mosaic Definition window outlines options for the definition of the mosaic output.
   

OPTIONS FOR MOSAIC DEFINITION

Mosaic output – Options for types of mosaic include:

1. Single file: Well suited for smaller, less complex projects. Entire mosaic is written to an individual file with a tile-definition layer of only one polygon shape.
2. Tiled: Well suited for larger, more complex projects. That is, when mosaicking large volumes of data, it is more practical to create the mosaic as a series of smaller tiles rather than one (potentially) large file.
3. Defined by polygons: uses a file you specify that has an existing vector-polygon layer containing the tile definitions to use for the mosaic.

Output file and Format – The Output file will be the file name of the final mosaic. The file extension you select will auto-populate the Format field. For example, <file_name>.pix or <file_name>.tif.

Channels and Channel mapping – The listed channel number is based on the source images. You can enter a different number of channels for the output mosaic (typically, to reduce number of channels) or map channels between the input and output images.

Output NoData – Enter one or more NoData values for the output imagery. For example, to specify NoData values for:

• Channels 1, 2, and 3 with -9999, 0, and 255, respectively, enter:  -9999,0,255
• Channels 2 and 3 (skipping Channel 1), with 0 and 255 respectively, enter:  ,0,255 (Note the comma before the zero.)

Resampling method – Options for resampling include:

1. Nearest neighbor: Most appropriate for discrete data. Although this method is efficient in computation time, it introduces small errors in the output image (e.g. spatial offset of up to half a pixel, which may cause a jagged appearance).
2. Bilinear interpolation: Appropriate for continuous data. Generates an image with a smoother appearance than nearest neighbor, but the gray-level values are altered in the process, which can result in blurring or loss of image resolution.
3. Cubic convolution (default): Appropriate for continuous data. The resulting image is slightly sharper than with bilinear interpolation and does not have the disjointed appearance produced by nearest neighbor.

Mosaic extents and Mosaic size – Change the extents by selecting a file from Define from file, or by dragging the blue Mosaic extents polygon in the viewer. If specifying a mosaic size (in Pixels and Lines), the Mosaic extents polygon will adjust automatically.

Projection Information – Specifies projection type (Pixel, UTM, Long/Lat, Meter, SPCS, or Other) and projection string.

Bounds and UL, LR coordinates – Specifies how to display the coordinates of the mosaic file:

1. Geocoded (easting, northing)
2. Geographic (latitude, longitude)

The UL and LR coordinates can be adjusted based on coordinate system.

2. Choose the appropriate options for your project.
   • For the tutorial, we leave all values as the defaults.
3. Click Next.

The New Project Wizard – Mosaic Preparation window opens.

2.3. PREPARING THE MOSAIC

Before you can generate a mosaic, you must first run mosaic preparation steps for the images that are added to the mosaic. This includes generating cutlines, applying colour balancing, determining sorting order, and applying normalization.

To prepare the mosaic:

1. The New Project Wizard – Mosaic Preparation window outlines options for preparing the images for the mosaic.
   
   

OPTIONS FOR MOSAIC PREPARATION

Compute cutlines – Methods used to compute cutline polygons to use for the mosaic include:

• Minimum squared difference: suitable for most mosaicking projects and in most cases produces the cleanest cutlines
• Minimum difference
• Minimum relative difference
• Edge
• Maximum data
• Import
• File extents

Apply color balancing – Evens out color contrast from one image to another to reduce visibility of seams and produce a visually appealing mosaic. Methods include:

• None
• Bundle
  • Note: In order to make use of advanced colour balancing tools such as dodging points you must use the Bundle method.
• Histogram
• Overlap area
• Reference image
• Lookup table
• Neighborhood

Sort images – Defines the order in which the images are added to the mosaic. Options include:

• Nearest to center
• Maximum intersection

For more information on preparing a mosaic, click on the CATALYST Help button or search Setting up mosaic preparation in the CATALYST Help.

2. Choose the appropriate options for your project. You can also choose to skip some or all of the mosaic preparation steps by un-checking the box beside the step.
   • For this tutorial, we leave all values as the defaults.
3. Click Generate Preview.
   • After the processing completes, the view pane in the wizard will be updated to show the imagery as it will appear in the mosaic. You can determine whether the mosaic is of suitable quality prior to generating the mosaic. If the preview is unsatisfactory, you can make changes on the Mosaic Preparation page to the cutlines, color balancing, sort order, or normalization.
     
4. At this point, you have the option to choose whether you are ready to generate the final mosaic or whether you want to apply further edits to the source images:
   • To generate the final mosaic, click Generate Mosaic.
     • When you generate the mosaic, a preview file is first generated, and then the output file is written to the folder and file name you specified.
     • Then click Finish to add the full mosaic to the Mosaic Tool.
     • At this time, the mosaic is complete. However, if you would like to restore the images for further editing, proceed to Section 5.
   • To manually edit the mosaic, click Finish. Proceed to Section 3.

Once you click Finish, the New Project Wizard closes and the project opens in Mosaic Tool.

3. SOURCE IMAGES EDITING (OPTIONAL)

In the Mosaic Tool window, you can review and make changes to any mosaic project created with CATALYST software (i.e. the .MOS file). You can modify cutlines, color balancing, normalization, or any other aspect to further improve the mosaic.

To open your mosaic project in Mosaic Tool:

1. From the CATALYST Professional Toolbar, open Mosaic Tool.
   
   
2. Select File > Open.
3. Navigate to the folder where you saved your output from the New Project Wizard. Open the .MOS file.

3.1. ORDERING IMAGES

The order of the images, as shown in the Source images list in the control pane, is determined by the Sort method specified during Mosaic Preparation. The first image in the list indicates the top-most position in the mosaic.

To change the order of the images, do one of the following options:

1. Drag and drop:
   1. From the Source images list, hold and drag an image to change the order that it appears in the mosaic. As you move the images in the list, the mosaic preview will be updated to reflect the changes.
2. Re-run Mosaic Preparation:
   1. Go to Tools > Mosaic Preparation. The Mosaic Preparation window opens.
   2. Uncheck everything except Sort images. Adjust Method or Starting image.
      
      iii. Click Run.
      iv. Once the sort has executed, click Close.

3. Change Z-order:
   i. Right-click on an image in the Source Images list and click Properties. The Layer Properties window opens.
   ii. Under the General tab, beside the Z-order dropdown, type or select a number to indicate the order in which the image will be added to the mosaic. A higher value represents top-most positioning. The mosaic image always has a z-order value of zero, meaning it is at the bottom of the image “stack.”
   
   iii. Click Apply, then OK.

3.2. WORKING WITH CUTLINES

When creating a mosaic, you want to crop the images so the best portions are seamlessly joined together. You can adjust cutlines to ensure that seams between images are not as noticeable.

Good cutlines should avoid:

• Buildings or man-made features, since they may lean in different directions in the imagery.
• Large bodies of water, because waves may look different in different images, and water tends to have different color in different images.
• Areas that are significantly different in color and texture, such as forests and cultivated land, since they may look different from image to image.

To edit a cutline:

1. Select an image from the Source images list.
2. Expand the image to ensure that the cutline is currently visible.
   
3. On the toolbar, click the Vector Editing icon  to open the Vector Editing Toolbar.
   
4. The Find tool  is selected by default. With Find selected, click on a cutline.
5. The cutline polygon becomes highlighted in teal. Two representations for cutlines are shown:
   • A solid cutline represents a visible cutline which is not obscured by other images in the mosaic.
   • A dotted cutline represents a hidden cutline, obscured by other images.
     
6.  Zoom in to a section of the image where you want to adjust the cutline. In the example below, we can edit the highlighted cutline to pass around instead of through the water.
   
7. Select the Reshape tool  from the Vector Editing Toolbar.
8. Begin to click along the feature where you want the new reshaped cutline to be placed.
9. Click Enter once you are done editing to exit the reshaping tool.
   

Note: To add vertices to the cutline polygon, use the Add Vertices tool . To move specific vertex, select it with the Find tool and drag it to a new location.

Note: To individually recreate cutlines for a single image, right-click the image and choose Compute Cutlines.

3.3. ADJUSTING NORMALIZATION

Some images may contain patterns in visual brightness that could affect the seamless integration of the images into the mosaic. Normalization evens out bright and dark effects and can help to achieve a more pleasing mosaic. You can apply normalization to all the images or individual images in the Source images list.

OPTIONS FOR NORMALIZATION

None – Does not apply any normalization.

Hot spot normalization– A common distortion in aerial and optical-satellite images, caused by solar reflections, is called hot spot distortion. Hot spot normalization removes distortion from aerial and optical-satellite images, which often appear circular in imagery. It normalizes brightness over the image by fitting a Gaussian surface to the brightness values. Hot spot normalization does not remove smaller spot reflections from lakes, cars, and buildings.

Adaptive filter normalization – For images that have a large, irregular bright-and-dark patterns that cannot be modeled to a Gaussian surface. Patterns that model to a Gaussian surface are better handled by Hot spot. Adaptive filter normalization adjusts the brightness and contrast over local areas, thereby improving image detail, while reducing the bright-and-dark pattern over the entire image.

• Note: Because of the intensive processing required, Adaptive filter normalization is not dynamic; that is, the display is not updated when you apply the command, but is applied in the output mosaic. Also, any color-balancing effects in the normalized image are visible only in the output mosaic.

For more information, search Applying Normalization in CATALYST Help.

For example, the images below show before (left) and after (right) hot spot normalization. 

To adjust normalization:

1. On a single image:
   • From the control pane, right-click image > select Normalize from dropdown > choose method.
2. On more than one image:
   • From the control pane, select multiple images > select the Normalize tool  dropdown from the toolbar > choose method.
3. On all images:
   • From the control pane, right-click the Source images header layer > select Normalize from dropdown > choose method.

3.4. PERFORMING COLOR BALANCING

Radiometric differences between images can cause a patchwork effect in a mosaic. Color balancing evens out the color contrasts from one image to another to reduce the visibility of seams and produce a visually appealing mosaic.

When running Mosaic Preparation in the New Project Wizard, a colour balancing method was chosen (See Section 2.3). However, there may still be areas of the mosaic that need additional adjustments.

DODGING POINTS

A key concept in color-balancing in a mosaic is the use of dodging points. A dodging point is a focal point on which you can make adjustments. You can add as many dodging points as necessary when adjusting the color balance of an image to give you more precise control over the area to enhance.

Note: In order to make use of advanced color balancing tools such as dodging points, you must apply the Bundle colour balancing method to your images.

To edit colour balancing:

1. Once you select at image, the Color Balancing Editing toolbar will become available.

3.4.1. USING EDGE DODGING POINTS

If you notice that the color does not match well at the cutline between images, use edge dodging points to perform color balancing. In this example, we balance the color of a roadway along a cutline.

Note: To use edge dodging points, ensure Bundle is selected as the Colour Balancing method.

Note: To check the seamline between two images, toggle on and off the cutline with the Display All Cutlines  button.

To use edge dodging points:

1. Select the image you would like to edit from the control pane.
   • In this tutorial, the left image is selected.
2. Click on the Add Edge Point  button and add a point to the cutline. You can change the behavior of the dodging point by clicking the small arrow beside the button.
   • If you choose Automatch Both Sides, both images will be automatically color matched when you add the edge point.
   • In this tutorial, Use Current Adjustment is selected.
3. Select the adjacent images from the control pane to see that there is an edge dodging point on both images.
   
4. Use the Dodging Contrast and Brightness dropdown menus to adjust the brightness and contrast of the left image – first coarsely, and then finely.
   
5. The adjustment is applied along the entire length of the cutline edge between other edge points.
   
6. To limit the extent of the adjustments, add additional edge points along to cutline. The following image shows an exaggerated example using additional edge dodging points. You will notice the brightness adjustment does not extend past the upper and lower edge dodging points.
   
7. Use the Adjust Pair Point  button to switch which side of the cutline (image) you are applying the dodging point edits to.

Note: Alternatively, instead of manually editing the brightness and contrast, click the Automatch Edge Point tool  to adjust the image. From the drop down, you can choose whether to adjust both images or the single image with the edge point.

3.4.2. USING FLOATING DODGING POINTS

Floating dodging points can be used to adjust a specific section in the middle of an image. In this example, we increase the brightness of an underexposed section of forest.

To use floating dodging points:

1. Select the image you would like to edit from the control pane.
2. Click on the Add Floating Point button  and add a point to the dark forest.
3. In order to isolate the color changes to a localized region, you can place other dodging points around the one you created.
   
4. For under-exposed regions, increase the brightness and lower the contrast. Notice that the changes will not extend past the cutlines and the other dodging points.
   
5. Place additional dodging points in the surrounding areas to extend the adjustments to other dark areas of the forest.
   
6. To view the result, select another image from the control pane to hide the dodging points.
   

3.4.3. ADJUSTING A SPECIFIC BAND

Instead of simultaneously adjusting the red, green, and blue (RGB) channels – or the bands assigned to these channels – you can further control how to balance color using dodging points.

To adjust the brightness/contrast of a specific band:

1. Open the Color Balancing Editing Settings  button.
2. Change the channel selection to a specific band. You can also adjust sensitivity, dodging, and sample size.
3. Click Close.

3.4.4. STORING COLOR STATISTICS

To compute and store regional color-balancing statistics, use the Store Statistics  and Automatch to Statistics buttons. The region you select can be a point, a rectangle, or a polygon. When you apply the stored statistics to any other dodging point, the color balancing of the region of stored statistics is applied.

To store the adjustment statistics:

1. Place one or more dodging points in the area that you want to adjust.
   
2. Using the Store Statistics tool , select an area with the desired color balancing – this can be a point, rectangle, or polygon.
   
3. Once you have the statistics stored, select the dodging point that you placed before.
   
4. Click the Automatch to Statistics  button. You may need to click this a few times to produce the desired results.

Note: Once your automatch is set, you can further improve the color by changing brightness and contrast.

3.5. USING MOSAIC GEOFILL

The Mosaic GeoFill tool allows users to alter aspects of their imagery, such as filling an AOI with content from an overlapping image to replace an unwanted aspect. Pixels are copied from the overlapping image and pasted to a new source images layer (called overlapping image_1). For example, you can use Mosaic GeoFill to replace clouds in an AOI with cloud-free pixels from any image in the Source images list that overlap the AOI.

The Mosaic GeoFill tools can be found on the Mosaic Tool Toolbar.

For more information about the functionality of each tool in the Mosaic GeoFill Toolbar, search About the Mosaic GeoFill toolbar in CATALYST Help.

3.5.1. DRAWING A POLYGON

A polygon is a vector element you draw on top of the image around the AOI: in this case, an area you want to repair. You draw a polygon by using a node-to-node selection technique where you click a starting node, and then progressively click to add each additional node to form the polygon you want according to the shape of the AOI.

To draw a polygon:

1. On the Mosaic GeoFill toolbar, click New GeoFill Polygon .
2. In the view pane, click to begin drawing the polygon, and click to add each node.

Note: To cancel the polygon at any point while drawing it, press the Esc key. This will cancel and un-select the GeoFill Polygon drawing tool.

3. To close the polygon once you have finished drawing the shape, double-click.
   • For the tutorial, we will be showing an example on a residential property since the images do not contain clouds.
     
4. The polygon will close from the last selection node to the first.

Note: To redraw your polygon, you can use the Reset Selection tool  to delete the currently drawn polygon. You will notice the polygon and copied pixels will be removed from the display.

You may need to reshape your polygon to include a large or smaller AOI.

To reshape a polygon:

1. On the GeoFill toolbar, click the Reshape tool .
2. In the view pane, click the polygon you want to reshape.
3. Click the vector at the location where you want to end the reshape.
4. To complete the reshape, double-click.

3.5.2. CHOOSING NEW PIXELS

Now that the AOI polygon has been drawn, you can view all the available images to choose the preferred alternative pixels to fill the polygon area.

To copy new pixels into the polygon, you have 3 options:

1. Manual scrolling: On the toolbar, click Previous and Next to cycle through the available overlapping images to find an image to fill the AOI.
   
2. Keyboard shortcuts: Press Ctrl+F for Next or Ctrl+D for Previous. To exclude an unsuitable image, press Ctrl+E.
3. Automatic scrolling: Click the Mosaic File Set tool  to open the Mosaic File Set window and automatically scroll through the candidate images. 
   
   • Click Play to initiate scrolling. The candidate images will automatically be displayed allowing you to view the best option to fix your image.
     
   • Click Stop at the image you would like to be copied.

3.5.3. BLENDING PIXELS

The blending tool allows you to control blending or smoothing of pixels around the perimeter of pixels to be pasted. A blending zone is defined as half the specified blend width, on either side of the edge of the GeoFill polygon. New pixel values in that zone are computed by combining original with copied pixel values.

Note: In areas containing bright or significantly different features, setting blend width too high may cause “ghosting” or “doubling” of features.

To smooth the perimeter of copied pixels:

1. With a polygon selected, click on the Set blend width tool .
2. Make sure the Use blend width check box is selected, and type the number of pixels to use as blend width.
   
3. To verify the suitability of the blend between the inside and outside of the polygon:
   • Click on the Show Selection Edge tool  to remove the polygon border.
   • Click and hold the Source Visibility tool  to compare the original image with the copied pixels.
4. Adjust the blend width value as required for your imagery.

3.5.4. COMMITTING CHANGES

Once you are ready to commit the changes you’ve made using Mosaic GeoFill, paste the new pixels into the source image.

To commit the changes:

1. After you are satisfied with the repair click the Paste tool . The polygon of new pixels is now saved as a source image layer, with the naming convention of <original_image>__1.
2. To visualize the extent of the blend width, you can unselect the rest of the source images to view the layer on its own.
   

4. FINAL MOSAIC GENERATION

The final step in the mosaic generation process is to add the edited source images to the defined mosaic. From your source images, you have the option to add all the images or individual images to the final mosaic file.

To add all the images from the Source Images list:

1. Right-click Source images and click Add to Mosaic.
   
   
   Note: If Add to Mosaic is not available from this drop-down menu, the mosaic file may not yet be defined. You can right-click Output Mosaic and select Define Output Mosaic. Alternatively, choose Tools > Define Output Mosaic.
   
2. The Mosaic Tool Progress window opens, and full mosaic begins to generate.
   • Note: The images are added to the mosaic file in the order that they appear in the Source images list.
     
3. Once the mosaic generation is complete, the images will be added to the output mosaic file and will no longer be available in the Source images list. Expand the mosaic file to check which images have been added.
   

To add individual images from the Source images list:

• Right-click the image in the Source images list and select Add to Mosaic.

5. IMAGE RESTORATION

After generating the mosaic file, you can choose to restore and reprocess any of the images if you notice a problem in the mosaic.

To restore the images:

1. In the control pane, right-click on the Output mosaic layer and select Restore to source.
2. In the Restore to Source window, select the images you would like to restore.
3. The images are reloaded into the Source images section of the control pane. Now you can edit and add the images back to the mosaic, as per Section 3 and Section 4, respectively.

6. ADDITIONAL TOOLS

Additional optional tools can be used in your mosaic project, particularly when working with larger mosaics that require verification from multiple users. The tools shown below include defining a working area of the mosaic and conducting quality control and verification.

6.1. MOSAIC OVERVIEW WINDOW

The Mosaic Overview window is helpful when working with large projects. You can easily examine the entire mosaic to identify areas to modify, then select the images and open them in the Mosaic Tool window. See the diagram below to see the elements of the Mosaic Overview window, including a working area.

A working area is an extent of images you want to display and modify in the Mosaic Tool window. All of the data from the overlapping images you select will be displayed.

Note: There are a number of options available from Mosaic Tool > Tools > Options. A particularly useful option is Performance – Bypass Mosaic Overview. When opening a large mosaic project, the mosaic overview window will open instead of automatically loading all images into Mosaic Tool (which can be time consuming). You can make an image threshold at which the Mosaic Overview window appears when you open a mosaic project.

To open the Mosaic Overview window:

1. On the Mosaic Tool toolbar, click on the Mosaic Overview button . The Mosaic Overview window opens with all images selected.
2. On the Selection toolbar, click  Select to define a new working area by doing one of the following:
   • To select an individual image: Click the image you want. To select the next overlapping image, and thereby use its extents, at the same location, click again. The selected images are now locked for editing by you, and other users can neither select nor edit the images.
   • To select an area: Drag to select one or more images. Each image that intersects the rectangle you draw is selected.
     
3.  After you select the images you want to modify, click Open Selection.
4. The selected images are opened in the Mosaic Tool window based on the defined working area.
   
5. You can edit the selection that was loaded as per Section 3.
6. Once the edits are complete, you can perform quality control and verification, as per Sections 6.2 and 6.3.

6.2. QUALITY CONTROL

Potential problems in the mosaic can be identified and flagged using the Quality control layer along with reference vectors and the mosaic preview. These problems can then be addressed before generating the final output mosaic.

To create a quality control layer:

1. From the Mosaic Tool main menu, select: File > New Quality Control Layer. (If the project already contains a Quality Control layer, this option is disabled.) The Quality Control Tools toolbar opens automatically.
   
2. The new Quality control layer appears under Auxiliary layers in the control pane.
   
3. In the Mosaic Tool view pane, zoom to an area that you want to flag for quality control purposes.
4. From Quality Control Tools, select the Add Point  icon.
5. Click your point of interest on the view pane to place the new point.
6. You can then add the type of point you are flagging and record comments.
   
7. To turn the layer on and off, clear the check mark beside Quality control in the control pane.
8. To save your progress, save the mosaic project. A file in the project folder will appear, called <project_file_name>_qc_layer.pix.

6.3. VERIFICATION

The verification tool is particularly useful with a larger mosaic. Once you have performed quality control on an image of your mosaic, you can change the status to reflect the verification progress. Typically, this is to change the status to Verified from the default, Unverified. Assigning a status helps you keep track of images you have and have not modified.

To use the verification tool:

1. In the Mosaic Tool window, click the Map Layer Selection tool .
2. Select the image or images for which you want to change status.
3. Click the Image Status dropdown  and select Verified or Unverified.
4. Images marked as Verified will appear in green.