PIXVELLO BLOG
How Image Compression Works and What It Changes
A plain-language explanation of lossy and lossless compression and the trade-offs behind smaller image files.
How image compression works and what it changes
Image compression reduces the amount of data needed to store an image. The goal is to make a file easier to store, upload or deliver while keeping enough visual information for its intended use.
Lossy compression
Lossy methods reduce file size by discarding some image information. JPEG is a common example. Stronger compression usually creates smaller files, but can introduce blockiness, ringing or loss of fine detail.
Lossless compression
Lossless methods represent image data more efficiently without discarding the original pixel information. PNG is a familiar example. The resulting file may be larger than a lossy version, especially for photographs.
Why two images compress differently
A detailed photograph, a flat-color illustration and a screenshot contain different patterns. Images with smooth areas may compress more efficiently than images full of texture, grain or tiny details.
Quality is more than a percentage
A quality slider is an encoder setting, not a universal measure of how good an image looks. Compare the exported result at the size it will actually be viewed.
A practical workflow
- Keep an untouched original.
- Choose a format that suits the image.
- Resize oversized dimensions when appropriate.
- Apply moderate compression.
- Inspect important details and file size.
Use the Pixvello image compressor to test output sizes, and Resize Image when dimensions are unnecessarily large.
Takeaway
The best compression setting is not necessarily the smallest possible file. It is the smallest file that still meets the visual and technical requirements of its destination.
Frequently asked questions
Does image compression always reduce quality?
Lossy compression discards some information and can reduce quality. Lossless compression reduces file size without losing the original pixel information.
Why do some images stay large after compression?
High pixel dimensions, texture, noise and fine detail can make an image harder to compress. Resizing may help when the destination does not need the original dimensions.
What is a good compression quality setting?
There is no universal setting. Use a moderate starting point, inspect the output at its intended display size and adjust according to the image and destination.