Image Rotation & Flip

All transformations run through the HTML Canvas 2D API in your browser. Rotation is applied with ctx.rotate(degrees * Pi / 180) after recomputing the output canvas to a bounding box of width*|cos| + height*|sin| by width*|sin| + height*|cos|, so the canvas always grows to contain the rotated image rather than cropping it. A 90 or 270 degree rotation therefore swaps the width and height, while an off-axis angle such as the built-in 45 degree preset produces a larger canvas with transparent triangular corners (preserved because the result is written as PNG). Flipping is done separately with ctx.scale(-1, 1) for horizontal mirroring or ctx.scale(1, -1) for vertical, and unlike rotation a flip keeps the original pixel dimensions unchanged.

The interface composes transforms in a fixed order on each apply: rotation first, then horizontal flip, then vertical flip, each as its own canvas pass. Rotation amount comes from three independent sources that are summed: the Quick Rotation buttons (90 degrees clockwise, 90 counter-clockwise, 180, and 45), a draggable circular dial that reads the pointer angle via Math.atan2 and snaps to whole degrees, and a separate Straighten control with preset buttons (-5, -2, -1, 0, +1, +2, +5) plus a slider that runs from -15 to +15 degrees in 0.5 degree steps for horizon correction. The Fix Phone Orientation buttons are shortcuts that set rotation directly: Portrait to 0, Landscape Left to 90, Landscape Right to -90, and Upside Down to 180. A 3x3 grid overlay, split-versus-single preview toggle, and CSS zoom help you check alignment before exporting.

Output is always a PNG encoded at quality 1.0 regardless of the input format, and the download is named from the original file with a suffix recording the operations, for example name-rot90-flipH.png. Two consequences follow from the implementation that are worth knowing. First, because every save re-renders through the canvas and re-encodes to PNG, this is a pixel-resampling pipeline, not a metadata-only or lossless re-tag of an existing JPEG; a JPEG you rotate comes back as a (typically larger) PNG. Second, the tool reads pixel data directly and contains no EXIF orientation handling, so the rotation you choose is composed on top of however the browser already displays the source image rather than reading or rewriting the camera orientation flag.