A photo of a form taken on a table has three problems at once. The page is tilted and trapezoid-shaped because the phone wasn't straight above it, the table shows around the edges, and one corner is darker than the rest. A scanner app fixes this by finding the four corners of the paper and stretching them back into a rectangle. The PDF Editor in the osFoundry desktop app does the same thing on your own computer, so the photo of a lease or an ID form never has to go through an online converter. The example below is page one of a made-up lease, photographed at an angle on a wooden table.
Open the photo in the PDF Editor
Open the PDF Editor from the app's Canvas and drag the photo into it. A JPG opens directly as a one-page PDF, so there is no conversion step first.
The page is tilted, a little dim toward the bottom right, and surrounded by wood. Everything outside the paper is going to be thrown away.
Let the editor find the corners
Open All tools, then Scan & OCR, then Enhance camera image. Four round handles appear on the photo, and they already sit on the corners of the paper. A hint at the bottom says to drag them onto the document's edges, which is only needed when the photo is messy, for example when a corner is hidden under a thumb or the paper is the same colour as the table.
Click Enhance page. The editor takes the quadrilateral inside the handles and stretches it into a straight rectangle, as if the camera had been looking straight down. The tilt, the table and the shadow along the edges are gone, and the text lines run horizontally.
Pick Black and white
A bar appears above the page with Original, Colour, Greyscale and Black and white, plus a Clean-up slider. Colour keeps the paper as the camera saw it, a faint yellow. Greyscale removes the colour. Black and white goes further and turns every pixel into either ink or paper.
For a document that will be printed, signed or sent back, Black and white is usually the right choice. It is also what hides the uneven lighting, because the result keeps only two values and the dim corner and the bright corner both end up as plain paper.
The effect can be measured. In this example the photo contains 253 different grey levels. After Black and white, the saved page has 2, ink and paper, and about 2.4% of its pixels are ink. The page measures 1243 × 1512 pixels. (The numbers come from reading the saved PDF's page image back with a script; they are for this example photo only.)
Click Done and save
Click Done in the bar, then the save icon at the top right. The editor writes a PDF to your computer, and the straightening and the black-and-white conversion both run there. Nothing about the photo is uploaded.
If the page needs more work, Crop pages and Organize pages are in the same bar.
The editor is part of the osFoundry apps, and the free desktop app can be downloaded from the osFoundry download page for macOS, Windows and Linux. How it keeps files on your own machine is described on the local-first page.
Top comments (0)