Registering Images
Image registration is a process of aligning two images acquired by the same/different sensors, at different times or from different viewpoints. Many image processing applications like remote sensing for change detection, estimation of wind speed and direction for weather forecasting, a fusion of medical images need image registration.
To register images, we need to determine a geometric transformation that aligns images with respect to the reference image. The most common transformations used are:
rigid (RST),
affine,
perspective.
The parameters of the geometric transformation are calculated based on a given set of tie-points.
The tie-points can be obtained manually or automatically as follows:
Manual method: in this case the algorithm will generate the registered image based on manually selected tie-points,
Automatic method: in this case, the tie-points are automatically generated by other algorithm comparing the input image with another reference image. The generated tie-points are later used by the register algorithm to generate the registered image.
Select PROCESSING → RASTER PROCESSING → REGISTER in the main menu.
File information
On the List of Layers select the raster layer to use as a reference. Optionally use Filter By Name field giving part of the layer name to help find the layer in the list.
Press the Next button to go to next step or the Cancel button to close the dialog.
On the List of Layers select the raster layer to be adjusted. Optionally use Filter By Name field giving part of the layer name to help find the layer in the list.
Press the Next button to go to next step.
Register information
The registration interface is composed of three components (Tie Points, Information and Reference/Adjust images) and several related tools. The details of each component are described bellow:
Tie Points - this component is used to handle the tie points and shows a group of tools used to add, update, select, remove, and also for automatic acquisition. The tie points are presented in the component Reference/Adjust images area. To handle the tie points use the tools described bellow:
- This tool is used
to update the tie points values if some of the geometric parameters
at the Information component were changed.
- This tool is used
to select all tie points to execute the registration.
- This tool is used
to unselect all tie points.
- This tool is used
to remove all selected tie points from the list.
- This tool is used
to acquire automatically tie points over the the images used as
reference and adjust.
- This tool is used
to finish the tie point acquisition step and shows the next step of
the registration method
Tie points status will be represented by changes on the point shape. Reference legend is indicated in the bottom of Information box.
Informations - (General and Options tabs) - it is used to define geometric parameters and also all options of specific parameters.
In General tab the following information are required:
Reference Band: Band of reference image to be used in register operation.
Adjust Band: Band of adjust image to be used in register operation.
Input SRID: Information about spatial reference system from image.
Input Resolution X: horizontal resolution of the image pixels.
Input Resolution Y: vertical resolution of the image pixels.
Output SRID: Information about spatial reference system from image.
Output Resolution X: horizontal resolution of the image pixels.
Output Resolution Y: vertical resolution of the image pixels.
Tie points number: Number of acquired tie points.
Transformation RMSE (all): Calculates root mean square direct mapping error for all tie points acquired.
Transformation RMSE (Selected): For selected tie points.
Transformation RMSE (Unselected): For unselected tie points.
In Options Tab it is possible to define specific parameters for each type of geometric transformation available. See the General, Moravec and Surf tabs:
Options → General
Options → Moravec
Correlation Window Width: used to correlate points between the images (minimum 3, default: 11).
Gaussian Filter Iterations: the number of noise Gaussian iterations, when applicable (used to remove image noise, zero will disable the Gaussian Filter, default:1).
Minimum Correlation: the minimum acceptable absolute correlation value when matching features (when applicable), default:0.5, valid range: [0,1].
Moravec Window Width: the Moravec window width is used to locate candidate tie-points (minimum 3, default: 5 ).
Options → Surf
Maximum Euclidean Distance: the maximum acceptable euclidean distance when matching features (when applicable), default:0.5, valid range: [0,1].
Octaves Number: the number of octaves to generate, when applicable (default: 3, minimum:1).
Scales Number: the number of sub-sampling scales to generate, when applicable (default:4, minimum:3).
Reference/Adjust images area: this component is used to show the tie points acquired in both images. There is one group of tools available to handle image composition. Using these tools it is possible to see the images in monochromatic, color composition, in red, green or blue channel. It is also possible to change the original color composition.
Also there is a
group of tools (vertical) to handle zoom in,
zoom out
,
pan
,
recompose
,
manual collection of a tie point
over the images. To help collect precise tie points there is a tool
to display
an small area beside both images highlighting and zooming the region
around where the cursor is pointing to. For the details on how to use
these tools see Raster Navigator.
After setting all
parameters click on the tool
.
Output information
Raster
Info - First press
and inform the folder where the resulting file will be saved.
Name - inform the raster name.
Extra Parameters - if there are some.
Press the Finish button to save the resulting registered raster or the Back button to go to the previous wizard page.
Note: Add the resulting raster to the TerraAmazon project and draw it together with the raster used as reference.
The Raster Navigator interface helps the user to view and acquire samples of the image. This component provides a set of tools that allows the user to navigate the raster. The interface consists of the following components:
Source: (TerraView 5.1.0, 2010).
Green Box: Allows the user to change the color composition of the raster. The set of buttons enables the user to define the color composition desired. Through the combo boxes is allowed to set the values of band for each channel.
Buttons of color composition: Gray, RGB, Red, Green and Blue.
Combo boxes for band selection:
Gray Band: index associated to the gray channel.
Red Band: index associated to the red channel.
Green Band: index associated to the green channel.
Blue Band: index associated to the blue channel.
Red Box: Tools for navigation on the raster.
Recompose,
Zoom Area,
Zoom Out,
Pan,
Sample Acquisition,
Enable/Disable extra displays.
Orange Box: Extra displays to aid in the visualization of raster.
Eye Bird: This display always shows the total area of the raster. A rectangle drawn on the display indicates the current display area of the main display.
Zoom In: This display is the central area of the main display on a larger scale. A slider allows scaling, helping the user to have a higher accuracy to acquire samples.
Blue Box: Information about the coordinate of the cursor on the raster. Both geographic and matrix coordinates are displayed.
Source: (TerraView 5.1.0, 2010).
The extra displays offer some interaction. The interactions made on these displays has direct effect on the main display.
Eye Bird: Is possible to drag the rectangle that defines the area of the current view to the area of interest.
Zoom In: Changing the scale of view through the slider bar or pan tool is available in this display.