Twitch has a 25 KB size limit for emotes and subscriber badges. Common image editing software such as Photoshop can create unnecessarily large files by including non-visible metadata and thumbnails or using low PNG compression.
This page lets you upload your emotes or subscriber badges and creates an optimized version with the smallest possible file size. All non-visible data is stripped away and the image data is recompressed with maximum compression. There is no quality loss from this process.