Straightening documents with Perspective Crop
Perspective Crop in Paint by Zaweba turns a tilted document, sign or painting in a photo into a flat rectangle by marking its four corners.
Photos of flat things are rarely taken straight on. A receipt snapped on a table, a whiteboard shot from the side of the room, a painting photographed at an angle to avoid glare. Perspective Crop in Paint by Zaweba takes such a photo and flattens the object back to a neat rectangle, as though it had been scanned.
Perspective Crop sits in the crop group of the toolbox, alongside the ordinary Crop tool. Press and hold that slot to see the flyout and pick it.
Marking the corners
Mark the four corners of the tilted object: the corners of the page, sign, board or canvas. The tool uses those four points to work out how the object sits in the photo, and when you commit, it is straightened and cropped to a rectangle.
Accuracy here is everything. Zoom in to place each corner exactly on the object's corner. If a corner is hidden or bent, as with a curled page, place it where the corner would be if the edges were continued.
Getting the size right
The result can be sized from the sides, worked out from the lengths of the edges you marked, or by typing a width and height. Typing is the better choice whenever you know the real proportions, such as a sheet of A4 paper or a canvas of known size, because the photo alone cannot always tell how tall a tilted rectangle really is. Sizing from the sides is fine for quick jobs where exact proportions do not matter.
Perspective Crop acts on all layers. If you have added notes or adjustments on other layers, they are straightened and cropped along with the photo, so everything stays lined up.
Jobs it handles
Saving receipts, letters and forms from phone photos. Capturing a whiteboard after a meeting. Photographing artwork and turning it into a straight image for a portfolio or a print. Pulling a sign, menu or poster out of a street photo so you can read it. Getting a straight texture of a door, a tile or a panel for use in other work.
Tips for better captures
Take the photo as square on as you reasonably can, since a strong angle stretches the far end of the object and loses detail. Light it evenly. Leave a little space round the object in the frame so all four corners are clearly visible. A sharp photo matters more than a perfectly straight one; Perspective Crop can fix the angle, but not blur.
Documents often look grey and uneven after flattening. Adjustment layers can brighten the paper and darken the text. For artwork, compare colours with the original under good light and correct if needed.
Where things go wrong
Corners placed slightly off, which leaves a sliver of background along one edge or cuts into the object. Letting the tool guess the size of a document with known proportions, so a page comes out squat. Very steep angles, where the far end has too little detail to rescue.
Which crop tool to choose
The ordinary Crop tool straightens by rotation and crops to a rectangle, which is right for tilted horizons but not for objects seen at an angle. Perspective Warp changes the perspective of whole scenes with several planes. Perspective Crop is the specialist for single flat rectangles, and in Paint by Zaweba it gets the job done in four clicks.
