A repeatable workflow for smaller delivery images
Good compression starts with the destination and a representative file. Choose dimensions and format deliberately, inspect the difficult regions, and keep the original as the master.
Choose a delivery goal before changing settings
Decide where the output will be used, its maximum display dimensions, and whether transparency is required. A product thumbnail, email attachment, and full-width photograph can need different copies of the same source. If the destination only displays an image at 1200 pixels, resizing a much larger source can save more than an aggressive quality reduction.
Auto output selects a broadly practical local format from the capabilities available in the current browser. Choose a specific format when compatibility, alpha, or a downstream workflow matters more than a general default.
Inspect the content most likely to break
For photographs, examine faces, hair, foliage, repeated texture, and smooth gradients. For graphics, focus on small text, one-pixel lines, flat fills, shadows, and transparent edges. Use the before-and-after view at the intended display size and at 100% when detail is important.
The default lossy quality is a review point, not a guarantee. Different images respond differently even when their dimensions and source format match. Test difficult representatives before applying one setting to a large batch.
Compare bytes and preserve the source
Check the output size as well as its appearance. A larger output usually provides no compression benefit unless the requested format conversion is itself the reason for the file. Ziply creates a new local download and does not overwrite the selected source.
Process still images only. Ziply screens APNG, animated WebP, and animated AVIF inputs because keeping only the first frame would be a damaging, silent change. Use an animation-aware workflow when every frame must be preserved.