Most format conversions on this site involve a tradeoff, lossy versus lossless, smaller versus higher quality. TIFF to PNG is unusual because it can be a conversion between two lossless formats with no quality tradeoff at all, assuming the source TIFF wasn't using JPEG compression internally. When a TIFF uses LZW or ZIP compression, or no compression at all, every pixel value is preserved exactly. PNG also preserves every pixel value exactly through DEFLATE compression. Converting between them is really just changing the container and the specific lossless algorithm used to pack the same pixel data, not discarding any information along the way.
The file size difference you see after conversion comes down to which lossless algorithm handles your specific image content better, not which format is more advanced. PNG's DEFLATE compression tends to do well on images with flat colors, sharp edges, and repeating patterns, the kind of content you find in scanned text documents, diagrams, and screenshots. TIFF's LZW compression handles some of the same content reasonably well but isn't always as efficient at it. For photographic content with continuous tone and natural noise, both formats struggle similarly since neither was designed with photography as the primary target. This is why converting a scanned document from TIFF to PNG often produces a smaller file, while converting a photographic TIFF might land close to the same size either way.
Why TIFF alpha channels are rare and where you actually find them
PNG was designed from the ground up with transparency as a core feature, which is why every PNG workflow assumes alpha channel support is available. TIFF predates that design philosophy by several years and added alpha channel support later as an optional extension rather than a core feature. The result is that most TIFF files in the wild, particularly anything coming out of a flatbed scanner or fax workflow, have no transparency at all because the software producing them never had a reason to include it. Where TIFF alpha channels do show up is in output from design and prepress software like Adobe Photoshop or InDesign, where a designer has explicitly created a transparent background and exported to TIFF rather than PSD or PNG, often because a print workflow specifically requested TIFF as the deliverable format.
The prepress and print connection that keeps TIFF alive
TIFF's continued use in professional printing and prepress work is its own distinct reason this conversion exists, separate from the scanner and fax document workflows. Print production software and commercial printing presses have historically required TIFF as an input format because it supports CMYK color space directly, which is how physical printing works, unlike PNG and JPEG which are built around RGB, the color model used by screens. A designer working on packaging, a magazine spread, or marketing material destined for print often exports a final TIFF specifically for the print vendor, while needing a separate PNG version of the same artwork for proofing on screen, uploading to a web preview, or sharing with a client who only needs to see the design rather than print it. That dual need is exactly the gap this conversion fills. If the same artwork also needs to go online afterward in a smaller format, the PNG to WebP converter takes the PNG output from here and brings it down further for web delivery without giving up transparency.