Greetings. preserves every pixel exactly. Quality loss enters through wrong tools: JPEG intermediates, silent downscaling, or flattening transparency against unwanted backgrounds. A PNG-to-PNG merge with matching dimensions is mathematically clean. How do I merge PNGs with different sizes? Decide the policy first: pad smaller images to the shared dimension (preserves all pixels, adds background), align and crop the excess (uniform edges, loses some content), or scale to match (uniform, but resamples pixels). Good tools make the choice explicit; bad ones scale silently. Can I merge PNGs with transparent backgrounds? Yes — transparency merges natively, with each image's alpha channel preserved into the combined file. Where transparent regions from different images overlap, the alpha values compose. For a flattened result instead, choose the background color explicitly during the merge rather than discovering white-on-white invisibility later.