Lossy vs Lossless Compression

A design export can be a 12 MB PNG. Marketing needs a 500 KB hero. Same photo, two compression philosophies. Archiving contracts as lossless PDF while emailing lossy review copies is normal. The word “compression” covers both.

Two strategies for smaller files

Lossless finds patterns and encodes them efficiently. Decode and you get the exact same pixels, samples, or vectors.

Lossy removes information the format treats as less important. Decode and you get something very close visually, but not bit-identical.

Neither is better in the abstract. They serve different stages. The same photo can exist as a large RAW, a lossless PNG, and a small JPEG. Each step trades fidelity for portability.

Lossless compression explained

Format	Lossless?
PNG	Yes (pixel-perfect)
FLAC audio	Yes
ZIP on text	Yes
GIF (256 colors)	Lossless for the palette; reducing colors first is lossy
H.264 at very high bitrate	Visually near-lossless, still technically lossy

Lossless fits when you might edit again, crop, or archive legal originals. Sizes shrink modestly compared with lossy exports. Flat graphics and screenshots with hard edges favor lossless formats. Photos with millions of colors rarely reach email-friendly sizes without lossy delivery.

Lossy compression explained

Format	Typical lossy behavior
JPEG	Blends color, drops fine detail
WebP (lossy mode)	Similar goals to JPEG, often smaller
MP4 / MOV video	Discards hard-to-see motion and texture
AAC / MP3 audio	Removes masked frequencies
PDF with downsampled images	Lowers resolution in embedded photos

Lossy settings use quality sliders, CRF, or video target file size. Aggressive settings show banding, mosquito noise, or blocky video. Flattening PNG transparency to JPEG for email destroys alpha permanently. Plan format before the first client send.

By media type

Images: PNG and TIFF for UI, logos, and transparency. JPEG or lossy WebP for photos on web and email. See compress images on Mac , compress JPG on Mac , and compress PNG on Mac .

Video: Mainstream delivery codecs (H.264, HEVC, VP9, AV1) are lossy. “Visually lossless” means high bitrate intermediates, not a different physics. See compress video without losing quality .

Audio: WAV and FLAC for masters. AAC and MP3 for sharing.

PDF: Vector text stays sharp. Embedded photos can be packed losslessly or downsampled. See compress PDF on Mac . Background terms: what is file compression .

Generational loss and re-saving

Opening a JPEG, editing one pixel, and saving again re-compresses the whole image. Repeat and banding grows. Keep a PNG or RAW master; export lossy copies for delivery.

Video works the same way. Re-encoding an MP4 for Slack, then again for email, stacks artifacts. Transcode once from the master.

Lossless PNG screenshots re-saved as PNG do not degrade. Converting PNG to JPEG is a one-way lossy step.

How to pick for your task

Scenario	Approach
Client logo with transparency	Lossless PNG
Blog hero photo	Lossy JPEG or WebP around 80 to 85 quality
Legal scan archive	Lossless PDF or TIFF
Slide deck email	Lossy image downsampling inside PDF
Bug video attachment	Lossy H.264 720p from the screen recording master
Family video archive	High-bitrate lossy or camera native; avoid repeated re-encode

When unsure, keep the lossless or high-quality master on disk and name the lossy copy for the channel (client-review.jpg, email-clip.mp4).

When a simpler export is enough

Preview, Photos, QuickTime, or Clipchamp can work when you need one lossy delivery copy and the default export clears the limit.

GetCompress fits when you repeatedly produce lossy delivery copies beside untouched masters: images, video, GIFs, and PDFs in one local queue, with quality presets and video target file size when forms list a hard cap. Preview before you save. Use the image comparison tool when you need a side-by-side check. It does not replace RAW editors or broadcast packaging suites. Document which exports are lossy in share notes so nobody upscales a JPEG expecting RAW latitude.