Frame types: Light Frame, Dark Frame, Flat-field Frame, Mask

Light Frames are your regular image exposures. Light frames contain the image you are trying to capture.  I typically capture light frames for 5 to 10 minutes. This typically results in at least 30 light frames.

Dark Frames are exposed at about the same time as the Light Frames and with exactly the same exposure settings (ISO and duration) but with the lens cap on. I usually capture dark frames while I am looking for other locations or compositions. Dark frames contain noise that is consistent across exposures. When using version 1.8 and earlier of Starry Landscape Stacker I recommend against the use of dark frames. This is because these versions of Starry Landscape Stacker did traditional dark frame subtraction and with traditional dark frame subtraction you need a minimum of 5x as many dark frames as light frames (10x would be better). Version 1.9 of Starry Landscape Stacker performs some novel processing on the dark frames to extract hot pixel and background glow without getting shot noise. Therefore, with some low-noise cameras, as few as 5 dark frames may be enough and most users will be happy with 10 dark frames.  With Starry Landscape Stacker version 1.9 I use 10 dark frames with my Canon 5Ds (not a low-noise camera). Here are instructions for preparing master dark frames.

Flat-Field Frames can be captured any time. They are captured with the lens settings (focal length, focus and aperture) and the ISO exactly as set for your light frames, but with the lens pointed at something that is perfectly evenly illuminated. If your lens were perfect, your flat frames would have the identical value at every pixel. The flat frames can be used to correct for vignetting and some errors in the sensor. If you are happy with the vignetting corrections provided by your raw converter then flat-field frames may not be worthwhile for you.  When you capture your flat-field frames you should also capture dark frames that are used with the flat-field frames to make a master flat-field frame. These darks frames will be exposed identically to the flat-field frames, but with the lens covered (and if necessary the whole camera covered with a dark cloth and in a darken room--the lens cap for one of my lenses lets in a lot of light so simply putting the lens cap on in a normally lit room is not enough to capture a dark frame). Here are instructions on preparing master flat-field frames.

A Mask is a single mask image created with a photo editor (e.g., Photoshop, Affinity Photo) or saved from a previous session Starry Landscape Stacker (the “-sky.tif” file written as the second file during the save can be used as input to Starry Landscape Stacker to supply a mask). The mask should have non-zero in the alpha channel for sky and 0 for ground. Supplying a mask to Starry Landscape Stacker allows Starry Landscape Stacker to skip the first two steps and jump immediately to aligning the light frames.

Last updated December 2023.