How to Stamp a Transparent PNG Logo Across a Batch of Photos in Swift
If you need the same logo on thirty photos, the boring bugs show up immediately: the mark looks huge on a 12-megapixel still and timid on a 48-megapixel one, the PNG’s transparent background turns into a grey box, or the edges of the logo go muddy because the alpha channel was applied twice. This post walks through a small UIKit pipeline that loads a transparent PNG, draws each photo, then draws…
When you need the same logo on multiple photos, the process can become tedious if not handled properly. The logo may appear too large on a lower resolution image or too small on a high-resolution one. Additionally, the PNG's transparent background can turn into a grey box, and the edges of the logo can become fuzzy due to the alpha channel being applied twice. This guide outlines a simple UIKit pipeline for loading a transparent PNG, drawing it onto each photo, and sizing it based on the photo's shorter side.
To begin, you must load the logo as a UIImage from your bundle or a file URL. It is crucial to keep the PNG's alpha channel intact, as converting it to JPEG will result in a non-transparent rectangle. If you support user-picked logos from the photo library, ensure you request the original file to avoid accidental sticker effects caused by using a JPEG preview from a share sheet.
The logo's appearance is determined by three factors: its visual size, its distance from the edges, and how it sits on top of the photo. Instead of using a fixed pixel size, you should size the logo relative to the photo's shorter side. For example, using 18% of the shorter side as the logo's width ensures consistent visual weight across different photo resolutions.
The LogoStampSpec struct defines these three factors, allowing you to easily adjust the logo's appearance by changing its relative width, edge padding, opacity, and corner position. By creating a UIGraphicsImageRenderer with the pixel size of the image, you can draw the logo onto the photo in pixel space, maintaining the correct orientation and ensuring the logo appears as intended across all photos in the batch.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
This story
This is one outlet's version. Read the fullest account.