# Master-flat frame

The master-flat frame is an image made of several flat images. The flat image is used in a process of CCD image calibration. To reduce a noise of a result, it is advisory to make a number of raw flat frames and combine them into one correction frame. The separate correction frame has to be used for each filter, if the color filters are used. Avoid eventual camera rotation on its mount.

## Creating a new project

First of all, we will create a new project. To begin with processing of a variable star observation, we create a new project. To do so, open the Project menu and activate the New item. A new dialog appears.

The dialog for making a new project.

Fill in a name that will be assigned to the project (1). Because the name of the file that keeps track of the data related to the project, the project file, is derived from the name, some characters cannot appear in the project name, do not use: / ? % * : | “ < and >.

The field Location (2) shows a path to the directory where a new project will be created. Edit the path to change the location, you can also click the Browse button to select a directory in a separate dialog.

Select a profile (3) to specify an intial set of configuration parameters into a new project. When you confirm the dialog, you should be in the main window again now. The table of input files shown there is empty.

The main application window with the table of input files, now empty.

See also

New project (dialog) and Main window

## Input files

Now, we are going to tell the program which files we are going to work on. These files are called the input files. Their list is displayed in the table in the main application window. When the application is closed, the list of files are saved to the disk and it is restored back when the program is launched again.

Supposing that the table now consists of files from your previous task, let’s get rid of them. Please, use Files ‣ Clear files to start a new task instead of just removing the files from the table. Besides the clearing the table of input files, this function resets all internal variables, too.

Now, we need to populate the table with the CCD frames we’re going to reduce. There are two methods how to achieve that - adding a individual files or adding all files from a folder. Which way is the best for you depends on organization of your observations on the disk. I’d suggest you to make a folder for each year, a folder for each night in it, the a subfolder for a name of object or another view field identification and finally a subfolder named upon the color filter (if you use more of them). In this case, the “Add frames from a folder” method is more convenient.

Click on Files ‣ Add frames from folder in the main menu. A new dialog appears. In the dialog, find a folder where the inputs files are stored in. Click on an entry in the Places pane to go to one of a preselected folders, double click in the middle pane enters the folder. The buttons in the upper part of the dialog shows your current position in the directory tree, you can use them to go to one of the parent folders. Enter the folder with the input files - you should see them in the middle pane. Then, click on the Add button to add files to the table of input files. The program shows the number of added files in the separate dialog. The Add frames from folder dialog is not closed automatically and allows a user to continue. Click on the OK button to close the dialog and return to the main window.

The “Add folder” dialog with the place selection box (left), the file selection box (middle) and the preview panel (right).

If you want to reduce only a subset of files from a folder, click on Files ‣ Add individual frames in the main menu. A new dialog appears, similar to the previous one. In the dialog, find a folder where the inputs files are stored in. Click on an entry in the Places pane to go to one of a preselected folders, double click in the middle pane enters the folder. The buttons in the upper part of the dialog shows your current position in the directory tree, you can use them to go to one of the parent folders. In the middle pane, select the files using the `Ctrl` modifier to include and exclude a single file and the `Shift` modifier to include a range of files. Then, click on the Add button to add selected files to the table of input files. The program shows the number of added files in the separate dialog. The Add individual frames dialog is not closed automatically and allows a user to continue. Click on the OK button to close the dialog and return to the main window.

The “Add files” dialog with the place selection box (left), the file selection box (middle) and the preview panel (right).

See also

Add frames from folder (dialog) and Add individual frames (dialog)

## Frame reduction

The next step is called the reduction process, even though there is no real “reduction” of the data. This is to keep the general scheme of data processing the same for all project types. In the standard calibration scheme, it is necessary to perform just two step - conversion of the source CCD frames into a working format and dark frame correction.

We will use the same Express reduction dialog as in the section Light curve. Using the menu, activate the Reduce ‣ Express reduction item. A new dialog appears. Check the option Fetch/convert files.

Check the Dark-frame correction option. Click the Browse button and find the file with the dark frame.

See also

Express reduction (dialog)

## Making master flat frame

Click on the Make ‣ Master-flat frame item. A new dialog appears. In the dialog, specify whether all files shall be processed or only the selected ones. Confirm the dialog. In the following dialog select a directory and enter the name of output file where a new master-flat frame shall be saved to. Press the Save button.

When a task is finished, a new preview window appears. A new master-flat frame is displayed in a separate window.

See also

Master flat frame (dialog)