Images & photos · Image Converter & Compressor
When lossy compression is the wrong call: originals, masters and text
· Why it matters
image-compression image-quality digital-preservation
Compression is a fine default for anything that will be viewed once on a screen, and a poor one for anything you will edit again, keep for years or need to read exactly. This post sets out the cases where lossless is the correct decision.
The archive that cannot be un-compressed — the moment someone discovers the only copy was a quality-60 JPEG
An archive has no “undo compression” command when its only surviving copy is a heavily encoded JPEG. A plausible preview can conceal lost texture, softened type or altered boundaries until somebody needs to edit, enlarge or analyze the image. Preservation decisions should therefore happen before storage is reduced, not after damage becomes operationally important.
Start by separating irreplaceable sources from delivery derivatives. Camera originals, scans and commissioned artwork belong in controlled storage with backups appropriate to their value. A web copy can be regenerated; the source cannot. ToolAcre should receive a duplicate when a lossy destination is being evaluated, never the sole archival file.
Lossy versus lossless in one sentence — what each keeps and what each throws away, and why 'visually identical' is not 'identical'
Lossless encoding stores the pixels it receives without an additional lossy approximation. Lossy encoding intentionally discards some detail to reduce output size. “Visually identical” means a viewer did not notice a difference under one condition; “identical” would require a stronger pixel or byte comparison. Those phrases should not be exchanged in preservation documentation.
ToolAcre marks JPEG and WebP output as lossy at every quality and PNG as a lossless encoder. Any resize still changes pixels before PNG encoding, so unchanged dimensions matter. A JPEG converted to PNG is not restored: the PNG simply keeps the decoded result of earlier loss. Format choice cannot recreate absent source information.
Case one: masters and originals — anything you might edit or re-export later should be kept lossless
Masters and originals should remain suitable for future edits and exports. Repeated lossy saves compound because each new encoder sees pixels produced by the prior generation. Keeping a master allows every campaign crop, thumbnail or attachment to be made as a first-generation derivative instead of extending a degradation chain.
A master need not be a PNG in every professional workflow; RAW, layered and specialized archival formats sit outside this tool. The product accepts a narrower raster set. The transferable principle is provenance: identify the best retained source, protect it, and record that delivery copies are disposable rather than silently promoting one compressed output into the new original.
Case two: screenshots and documents — text, lines and flat colour, where artefacts are both visible and misleading
Screenshots and documents place meaning in text edges, thin rules and flat areas. Lossy artefacts can make small characters harder to read or change the apparent boundary of a diagram. PNG often fits this content because its encoder preserves supplied pixels and alpha, although a resize can still compromise one-pixel details.
Test at the actual reading size, including high-density and zoomed contexts where relevant. A byte reduction is not beneficial if a support screenshot no longer shows the error text or a scanned signature becomes ambiguous. Accessibility and evidentiary clarity outrank an arbitrary attachment saving.
Case three: images that will be analysed — diagrams, charts, scans and anything where a pixel value carries meaning
Charts, diagrams, scans and scientific or inspection images may carry meaning in individual values and boundaries. ToolAcre does not know that semantics and cannot certify a lossy export for analysis. If downstream software measures pixels, keep the documented source and validate any transformation with the domain’s own method.
Even lossless PNG output may be unsuitable after colour-profile conversion, bit-depth reduction or canvas resampling. The config warns that profiles are not carried through the canvas, and the browser pipeline does not promise preservation of high bit depth. Analytical fidelity requires a format-aware path beyond a general web canvas.
Where lossy is still right — final delivery copies, web display and photographs viewed at screen size
Lossy output remains appropriate for many replaceable photographs displayed at screen size. A final blog hero, newsletter photo or preview can trade imperceptible detail for fewer bytes when an editor inspects the candidate and retains the master. The important word is “final”: geometry and content decisions should settle before the delivery encode.
Select JPEG for an opaque photograph when compatibility favors it, or test WebP where alpha or that destination format is useful. ToolAcre measures each result rather than promising a reduction. Accept the derivative only when its actual size and appearance meet the delivery requirement; otherwise retain a larger output.
Worked example: sorting a mixed folder into keep-lossless and compress-for-delivery — applying the rules
Duplicate a mixed folder containing camera photographs, screenshots, a scanned agreement, a chart and logo artwork. Mark photographs intended only for a web gallery as delivery candidates. Keep the screenshot and chart lossless, preserve the scan under its records policy, and retain the logo’s alpha-capable master. Document any uncertain item instead of guessing.
Run only delivery candidates through the converter, using dimensions chosen for their destinations. Save outputs in a separate folder and compare them to the masters. No compression ratio is assumed, because each content type and browser encode differs. The sorting decision is the worked result; byte totals are observations collected afterward.
Takeaway: compress copies, not sources — how the Image Converter & Compressor supports both, and why PNG stays lossless whatever the slider says
Compress copies, not sources. That rule permits aggressive experimentation because a failed derivative can be deleted and regenerated. It also clarifies ToolAcre’s dual role: PNG can provide a lossless output from unchanged canvas pixels, while JPEG and WebP provide explicitly lossy delivery choices.
The tool cannot decide archival value, analytical tolerance or legal retention. Those decisions belong to the owner of the material. Once they are made, the converter can execute a bounded plan honestly—named destination, visible warnings, measured bytes—without pretending every smaller file represents progress.