Image Compression
What image compression is, lossy vs lossless explained, and common mistakes when compressing screenshots.
Image compression reduces the number of bytes needed to store an image. Lossless methods remove redundancy, so the decoded pixels match the original exactly. Lossy methods also discard detail the eye is less likely to notice, which produces much smaller files.
Uncompressed images are large. A 1920×1080 image with 3 bytes per pixel needs 1920 × 1080 × 3 = 6,220,800 bytes, about 6.2 MB. A Retina capture of the same screen area has four times as many pixels.
The compression ratio is the original size divided by the compressed size. It depends on the content: flat interface screenshots compress far better than photos or noisy gradients.
Convert image formats
Changing the format is often the quickest way to change compression. Image Converter converts between PNG, JPG and WebP in the browser.
Lossy vs lossless compression
| Lossless | Lossy | |
|---|---|---|
| Decoded pixels | Identical to the source | Approximate |
| Typical size | Larger | Smaller |
| Re-saving | No further loss | Loses more each time |
| Examples | PNG, GIF, WebP lossless | JPG, WebP lossy, AVIF |
Where image compression matters
- Email attachments and chat apps with size limits.
- Web pages, where image bytes affect load time.
- PDFs built from many screenshots.
- Archives of long capture sessions with hundreds of frames.
Common formats and their compression
- PNG: row filters plus DEFLATE, lossless.
- JPG: DCT and quantization, lossy, with a quality setting.
- WebP: lossy (VP8-based) or lossless mode.
- GIF: LZW on a 256-color palette.
In Temposhot, the results pane offers PNG Export (Lossless) and JPG Export (Adjustable Quality) with quality 1-100, default 85. Website Capture saves JPEG, PNG or WebP, with quality 1-100 for JPEG and WebP.
Common mistakes with image compression
- Saving screenshots with small text as low-quality JPG, which blurs letters.
- Recompressing the same JPG many times.
- Converting a JPG to PNG and expecting the lost detail to return.
- Compressing the master copy instead of a copy for sharing.
Have an image to fix right now?
Reduce file size in the browser with Image Compressor. For a PDF, use Compress PDF.
Common questions
Which quality setting should I use for screenshots?
Start at 85, the Temposhot default for JPG, and compare a zoomed crop at a lower value before going smaller.
Does compression change pixel dimensions?
No. Compression changes how pixels are stored. Resizing changes how many there are.
Sources
Related resources
- Export formats: PNG, JPG, WebP, GIF, MP4 and PDF.
- General and history settings: Auto Export JPG quality.
Taking the same screenshots again and again?
Temposhot captures a screen, window or area on a timer and exports the set as a PDF, images, ZIP or MP4. The free browser tools fix single images.
Related resources
Related terms
- Lossy CompressionWhat lossy compression is, which image formats use it, and how to balance file size against visual quality.
- Lossless CompressionWhat lossless compression is, which image formats support it, and when pixel-perfect preservation matters.
- Image OptimizationWhat image optimization is, how it affects web performance, and mistakes to avoid.
- Image QualityWhat determines image quality, how quality interacts with file size, and how to choose the right quality settings for screenshots and exports.
- Image FormatOverview of common image formats — PNG, JPG, WebP, AVIF — and when to use each.
- Image RedactionWhat image redaction is, how it differs from blurring and cropping, and how to redact properly before sharing.
- JPGHow JPG compression works, when to use it vs PNG and WebP, and common mistakes with lossy screenshot formats.
- PNGHow the PNG image format works, when to use it for screenshots, and how it compares to JPG and WebP.