compressthemall
Underpressured is an image optimization and conversion tool for folders and folders of images. A single picture is welcome too, but there's no need to form a queue. Plenty of apps can compress pictures. None of them do it as simply as Underpressured, and the simplicity doesn't cost you any quality.
Presets
For when “same as last time” is exactly what you want.
Save the output format (JPEG, PNG, or the original), the compression (lossy or lossless), and resizing by width, height, or the longer side. Then pick the whole setup in one click.
Place
Smaller files shouldn't mean a bigger mess.
Replace the originals without a trace, send them to the system Trash, or leave them alone and save the compressed copies anywhere you want. Nested folders keep their structure.
Result
See how much weight each image lost.
Underpressured lists the new size and the percentage of change. It's interactive too: preview with Quick Look, open a file, or reveal it in Finder.
For the curious
Codecs under the hood
- jpegli JPEG
- Progressive encode at the preset quality. Lossless mode rewrites the file without touching its coefficients; resized or converted JPEGs get a visually lossless encode.
- quantizr PNG, lossy
- Searches for a smaller palette and keeps it only when the result stays above a quality floor. Otherwise it falls back to full color.
- oxipng PNG, lossless
- Optimizes the file at level 2 without changing a single pixel.
- vImage Lanczos Resize
- Resizes in linear light and keeps the aspect ratio. Images are never enlarged.
That's it. Easy as . Just works.