Why does my transparent PNG turn black when I convert it to JPEG?

JPEG has no alpha channel. When ImageMagick discards it, transparent pixels keep the RGB value stored underneath, which is usually black. Fix it with -background white -alpha remove -alpha off.

How do I convert images to WebP with ImageMagick?

Name the output with a .webp extension and set the effort level: magick input.jpg -quality 80 -define webp:method=6 output.webp. Check support first with magick -list format.

How do I reduce JPEG file size without visible quality loss?

Combine -strip, -interlace Plane, -sampling-factor 4:2:0 and -quality 82. That typically cuts 40 to 60 percent with no visible change on photographs.

Why does ImageMagick say no encode delegate for this image format?

The format was not compiled into your build. Run magick -list format to see what is available. No command-line flag can add a missing delegate library.

ImageMagick convert & compress command generator

Convert between image formats with ImageMagick and compress properly. Correct flags for JPEG, PNG, WebP and AVIF, plus the fix for transparent PNGs turning black.

ImageMagick picks its output encoder from the file extension, not from a flag. Naming the output photo.webp is what selects WebP. Everything else is about telling that encoder how hard to work.

Optimise a JPEG for the web

magick input.jpg -strip -interlace Plane -sampling-factor 4:2:0 -quality 82 output.jpg

-strip removes EXIF, comments and colour profiles.
-interlace Plane makes it progressive, so it renders blurry-then-sharp instead of top-to-bottom.
-sampling-factor 4:2:0 halves the colour resolution. Invisible on photographs, but it smears fine coloured text and thin red lines — turn it off for screenshots and UI mockups.
-quality 82 is the usual sweet spot. Below about 75 artefacts become visible on skin and sky.

Transparent PNG to JPEG without a black background

The most-reported ImageMagick surprise. JPEG has no alpha channel, so when it is discarded the transparent pixels keep whatever RGB was stored underneath — usually black.

magick input.png -background white -alpha remove -alpha off output.jpg

-alpha remove composites against the background first; -alpha off then drops the now-redundant channel. -background must come before both, because it is a setting rather than an operator.

Convert to WebP

magick input.jpg -quality 80 -define webp:method=6 output.webp

method=6 is the slowest and smallest effort level. On photographs, WebP at q80 is roughly the size of JPEG at q65 for the same perceived quality. For graphics with flat colour, use lossless instead:

magick input.png -define webp:lossless=true output.webp

Shrink a PNG

magick input.png -strip -define png:compression-level=9 output.png

That is lossless. For a much bigger win on logos, screenshots and illustrations, quantise to a palette:

magick input.png -strip -colors 256 -define png:compression-level=9 output.png

Check what your build actually supports

Format support is compiled in, not enabled by a flag. Before debugging an AVIF or HEIC command, check whether your binary can write it at all:

magick -list format | grep -iE 'avif|heic|webp'

Each line ends with read/write permissions. If a format shows r-- you can read it but not write it, and no command-line option will change that — you need a build with the right delegate library.

A warning about -strip

-strip also removes the ICC colour profile. On images from a wide-gamut camera or a Display-P3 phone, dropping the profile without converting the pixels first makes colours visibly shift — usually flatter and duller. The safe order is:

magick input.jpg -colorspace sRGB -strip -quality 85 output.jpg