Trim Image Section

The Trim Image Section command extracts ("crops") a rectangular area of an image with the option to take the trim region description from a FITS format image header. This procedure is often applied to trim away "overscan" and "underscan" Bias regions and dark reference pixels from a CCD frame after the Bias and dark corrections have been made. The keyword used to describe the trim section as part of the whole image is often named TRIMSEC. The ability to specify the trim range is also offered and, in that mode, it works the same as the Crop Image command. For less precise interactive trimming, see the Crop at Cursor command.

The Trim Image Section command opens from the Image Window > Process > Calibration menu and button on the Main Toolbar. The "immediate" form, shown first, opens when an image or image set is displayed in the top-most window. The general form can be used to select source images from folders, windows, or by matching templates.

Trim Image Section Properties

Profile [|>]

Selects the parameter profile for this command and allows you to save or work with existing presets.

[Select]

Opens the Select Source Images dialog to choose images from an image window, folder, files, pattern, or a file list.

Trimming options

Image Section Keyword

Select this bullet to trim using a keyword from the image header. Specify the keyword name and whether it uses non-standard 0-based coordinates. The keyword is a so-called "section" type keyword having a specific format. The standard convention is that the keyword is named TRIMSEC. Use the [+] and [x] buttons to add or delete the currently displayed entry. See FITS Keywords.

Section uses 0-based coordinates

Check this box if the trim section keyword uses non-standard 0-based coordinates. FITS format requires 1-based coordinates but some camera control software does not follow the standard. See Coordinate Systems and particularly Pixel Coordinate Definition.

Range

Select this bullet to enter the trim rectangle in terms of columns and rows.

Min, Max Column, Row

Specify the column and row limits to be processed. This is always be expressed in terms of unit-based coordinates in which the first pixel of the image is number 1.

The Max Column and Max Row values can be negative, to use a "high end offset" measured relative to the maximum dimension of the image. For example, setting Max Column = -2 trims 2 pixels from the maximum column number of the image.

Related Topics