Auto Upright

Straightens a photo the way Lightroom's Upright does: it finds the lines in the picture, then levels the horizon or makes the building verticals parallel. If it is not sure, it leaves the photo alone.

In ComfyUI	Add Node → ComfyUI-JH-PixelPro → geometry → Auto: Upright
Good for	Tilted horizons, buildings shot looking up, interiors, architecture and real-estate photos
Speed	About 0.1 to 0.3 s per image, VRAM under 0.3 GB

When to use it

Tilt the camera up at a building and the vertical lines lean toward each other. Hold the camera slightly rolled and the horizon is crooked. This node measures both from the straight lines in the photo and corrects them with no sliders to guess.

It only acts when the evidence is clear. Portraits, trees, clouds or noisy scenes have no reliable lines, so the image comes back unchanged and confidence is 0. A wrong guess would be worse than no correction.

Quick start

1. Load Image → Auto: Upright → Preview Image.
2. Keep mode on auto. Set crop to valid for a clean final image.
3. If a tall building looks too rigid, lower strength to about 0.7.
4. Watch the confidence output (connect it to a text preview). 0 means nothing was changed.

Settings

Setting	Default	What it does	Tip
image		The photo or batch to straighten.
mode	auto	auto = parallel verticals if buildings are found, otherwise a level horizon. level = rotate only. vertical = parallel verticals. full = verticals plus the main horizontal lines.	level for landscapes and seascapes. full for a facade seen straight on.
strength	1.0	0 to 1. The fraction of the correction to apply.	About 0.7 keeps a natural bit of perspective in tall buildings.
crop	none	none keeps everything, with black corners where the picture was turned. valid zooms in until no empty corners remain.	valid for final output.
max_angle (optional)	25	0 to 45 degrees. Larger corrections stop at this angle.	Steep look-up shots are corrected part of the way instead of being stretched too far.

Outputs

Output	What it is
image	The straightened image, same size as the input.
confidence	0 to 1, the lowest value of a batch. 0 means the image was left unchanged.
matrix	Text (JSON) list of the 3x3 pixel transforms that were applied, one per image.

Tips from retouching

• Run Auto Upright before Auto Tone and other colour work, so you measure the final framing.
• With crop set to none, the corners go black. Use valid, or crop yourself, before you send the picture on.
• Strong wide-angle distortion bends lines too. If lines curve near the edges, fix that first with Lens Distortion.
• Use level when the scene has only a horizon and no buildings. It will not invent a perspective change.
• A confidence of 0 usually means the photo has too few long straight lines, or its verticals lean more than 15 degrees, which are not treated as walls. Straighten it by hand or try level.

Under the hood

Straight line segments are found with OpenCV's line segment detector on a copy whose long edge is at most 1024 px. Source: core/upright.py, wrapper nodes/upright_node.py.

level: the tilt is the length-weighted median of the near-horizontal and near-vertical lines, and the photo is rotated about its centre.

vertical / full: vanishing points are found by RANSAC, then refined. The camera is virtually rotated (H = K·R·K⁻¹) so the vertical vanishing point goes to infinity and the verticals become parallel. full also does this for the main horizontal point. Focal length comes from the two points when they are orthogonal, otherwise a default of about a 36 mm lens.

Safety gate: level needs at least 3 lines, enough total length and 60 % of that length in agreement. A vanishing point needs at least 5 lines and agreeing lines totalling half the long edge. Lines leaning more than 15 degrees are not treated as walls. Otherwise the image is returned unchanged with confidence 0.

The warp runs with Kornia on the image's device. crop valid zooms to the largest rectangle of the original shape that holds only image pixels.

Related nodes

• Auto Tone: fix exposure and white balance after straightening
• Lens Distortion: remove barrel or pincushion bending before straightening
• Auto Align: align a series of photos to each other

Example workflow

Auto Upright example workflow: a church photo shot looking up is straightened with crop set to valid, then goes through Auto Tone. It uses only core ComfyUI nodes and this pack. Copy workflows/sample_architecture.jpg into ComfyUI/input/ (Pexels License).