After loading a file, the contents are shown in the LN DRS Image GUI window (see figure 1). If the file contains several images (several position angles), the first image is displayed.

Figure 1: A loaded image is shown in the LN DRS Image GUI window.

This window provides the following functional interface:

1. The file name of the image currently shown in the window.
2. A mouse click on the <-button switches to the preceeding image (lower image number).
3. A mouse click on the >-button switches to the following image (higher image number).
4. The current color map can be switched by using this option menu.
5. These tools are necessary to parameterize the preprocessing, target preprocessing and PSF preprocessing steps.

The toolbar in the image window (see figure 2 and table 1) provides tools for navigating a loaded image, getting information about a part of an image or creating and modifying objects necessary for specific data processing steps (for example, creating reference stars for the preprocessing step).

Figure 2: Toolbar in the LN DRS Image GUI window.

Except for the view tool and the info tool, each tool has an accompanying object which is created, manipulated and deleted through that tool.

Table 1: Predefined tools

Icon	Name	Description
	View tool	Provides functions for zooming and panning images.
	Reference star tool	Provides functions for creating and modifying reference stars (preprocessing step).
	PSF star tool	Provides functions for creating and modifying psf stars (psf preprocessing step).
	Target tool	Provides functions for creating and modifying targets (target preprocessing step).
	Info tool	Provides access to created objects and their specification.
	Probe tool	Provides statistical information of an image part.
	Pixel tool	Provides information about an individual pixel and its direct neighbours.
	Halo tool	Creates and modifies a target halo (psf preprocessing).

This tool provides functions for zooming and panning (moving) an image in the LN DRS Image GUI window. Other tools also include this function, but the Shift key must be pressed simultaneously.

The zoom function is equivalent to binning or enlarging pixels. The zoom steps are integral values. This means that the values go from -20 to 20, where positive numbers mean enlarging (zooming in) and negative values shrinking (binning). A value of 0 means a 1:1 image display.

The info tool provides access to the information of graphical objects. By selecting this tool and an existing object with the left mouse button, the dialog window containing the object-specific data is shown. In addition, the functionality of the view tool is still available by pressing the shift key simultaneously with a mouse button.

The probe tool allows the creation and modification of image probes. These probes define an image part and show statistical information about that part. The primary purpose of an image probe is to give information about the background.

Figure 3 shows the the graphical representation of an image probe and the dialog window with the statistical information. It is possible to automatically recenter the image probe by using the intensity peak, intensity mean or fourier phase (see section Recentering objects).

Figure 3: Graphical representation and dialog window of an image probe.

The dialog window of an image probe shows the following information:

1. The label of an image probe is automatically created and updated.
2. The position and size of an image probe uses integral values. It is possible to recenter the image probe or set the position and size explicitly. The Update button recalculates the statistical information after changing the position or size of an image probe.
3. The sky background specification is based on the image probe area. These values give only a rough estimate of the sky background.
4. The integral intensity (using all pixels inside the probe) and number of pixels are shown here.
5. The smallest and largest pixel value in the probe area and their positions (relative to the complete image) are shown.
6. The centroid is equal to the intensity mean.
7. The statistical data gives useful information about the sky background:
   • If the mean and variance have the same value, the background is dominated by poisson noise and no addditional point sources exist inside the probe area. The mean value then gives a good estimate for a constant sky background.
   • A skew value not equal to zero (including a small uncertainty range) is a strong hint that the background is contaminated with weak point sources.

The pixel tool and the accompanying pixel object shows information about one pixel and compares the value to the nearest eight pixels.

Figure 4 shows the graphical representation of a pixel probe and the dialog window with the statistical information. It is possible to automatically recenter the pixel probe by using the intensity peak, intensity mean or fourier phase (see section Recentering objects).

Figure 4: Graphical representation and dialog window of an image pixel.

The dialog window of an image pixel shows the following information:

1. The label of an image pixel is automatically created and updated.
2. The position of an image pixel uses integral values. It is possible to recenter the image pixel or set the position explicitly. The Update button recalculates the statistical information after changing the position of an image pixel.
3. The values of the selected image pixel and the eight neighbors are shown. The orientation in the dialog window and in the displayed image is identical.
4. The statistical information uses only the neighbor pixels; the central pixel is ignored.
5. The deviation describes the pixel value as mean + σ × deviation. If the deviation is too big, the central pixel may be a defect pixel.