Rotate and Flip
Step: Linear
Turns the image by a quarter or a half turn, or mirrors it. Use it to bring a frame into the orientation you want, for example when the camera was mounted sideways, or to match the orientation of a reference chart. Nothing is recalculated: every pixel keeps its value and only moves to a new place, so the operation loses no quality and can be undone exactly by the opposite one.
Parameters
| Parameter | Range | Default | Effect |
|---|---|---|---|
| Operation | 90° clockwise, 180°, 90° counterclockwise, Flip horizontally, Flip vertically | 90° clockwise | 90° clockwise and 90° counterclockwise turn the image by a quarter turn. 180° turns it upside down. Flip horizontally mirrors left and right. Flip vertically mirrors top and bottom. |
How it works
Each pixel of the result is a copy of exactly one pixel of the original, with no interpolation in between. After a quarter turn, width and height trade places: an image of 3000 × 2000 pixels becomes 2000 × 3000. Mono and color images are handled alike, every color channel moves the same way, and the file information (exposure time, filter and so on) is kept.
Four quarter turns in the same direction give back the original image, and so do two identical flips.
An undebayered image carries a Bayer pattern that names the colors of its top-left pixels. Turning or flipping moves other pixels to the top-left corner, so Siderea updates the pattern to match. Which pixels these are can depend on whether the width and height are odd or even; Siderea takes that into account, so Debayer still gets the colors right afterwards.
Tips
- Rotate and flip before any other geometry step. A crop after a turn counts its margins in the new orientation.
- Flipping mirrors the sky. Use it only to correct a mirrored image, not to change the framing.