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Practical guide · 4 min read

How to compress images without obvious quality loss

Good compression is not about choosing the lowest possible quality. It is about removing pixels and detail that the intended display cannot use, then checking the result in context.

By Filemivo · Published · Updated

Resize before adjusting quality

An image displayed at 1200 pixels wide rarely needs to be delivered at 5000 pixels wide. Reducing dimensions first often saves more data than aggressive compression and usually produces a cleaner result.

Export at the largest size the design actually displays, allowing extra resolution only when high-density screens or zooming genuinely require it.

Match the format to the content

Photographs compress efficiently with lossy WebP or JPG. Flat graphics, transparency and small text may look better in PNG or lossless WebP.

Converting a poor-quality source into a newer format cannot recreate detail that is already gone. Always begin with the best source available.

Compare at realistic and full size

Check the result at the size visitors will see it, then inspect important edges and gradients at 100% zoom. Look for blockiness, colour banding, halos around text and smeared detail.

If the output looks damaged, increase quality in small steps. If it looks identical, lower quality gradually until the first visible problem and then move one step back.

Worked example: resize a 4000 × 3000 photo

For a target width of 1200 pixels, enter a height of 900 pixels in Image Resizer. Both fields are used, so entering 1200 × 1200 would stretch this photo into a square. The main resize action exports PNG; use the compressor afterwards when JPG delivery is appropriate.

Start compression at the default 82% quality. Compare the downloaded file with the source, then try a lower or higher setting based on visible detail. The compressor keeps dimensions unchanged and its main action exports JPG, including for PNG input. Transparent pixels become white.

Record bytes, not just a quality percentage

Record the source size, output size, dimensions and quality setting for each trial. Calculate the reduction as (source bytes − output bytes) / source bytes × 100. For illustration only, a 2,000,000-byte source and a 500,000-byte output represent a 75% reduction; these numbers are not a measured Filemivo result or a promised saving.

If the output is larger, keep the original or try another format. For a strict upload limit, check the actual byte count rather than a rounded KB display. There is no automatic target-size setting.

Use a repeatable workflow

Keep the source, record the intended display dimensions and compare file sizes only after visual review. This makes later updates consistent.

  • Copy the original before processing.
  • Resize to the required dimensions.
  • Try WebP and the format already used by your workflow.
  • Inspect the output and retain the smallest acceptable version.