Contrast on poor scans: rescue text without destroying it

Dark file copies and grey fax descendants are routine. Contrast enhancement can make characters readable - or wipe lines, punctuation and thin digits. The difference is measure and control, not merely having a filter.

Diagnose first, then filter

If the whole page is too dark, moderate brightening often helps. If a grey veil sits over otherwise sharp type, contrast can save OCR. If characters are already smeared or heavily compressed, boosting creates artefacts. Then a new scan or better source is the honest fix.

Colour stamps and markings are sensitive: harsh greyscale contrast can destroy stamp information later contested.

Working checklist

• Compare before/after at 100-150% zoom.
• Check case numbers, amounts and table lines deliberately.
• Note filter strength when treating similar pages alike.
• Do not hit every page in the pack with the same aggression.
• Keep the original scan untouched.
• After contrast: OCR spot check, not only the visual look.

With deskew and OCR

Straighten skewed dark pages before exposure - or you amplify artefacts along the skew. Dual-engine comparisons show quickly whether improvement produced text or only “nicer grey”. LexLogik offers enhancement in the browser workflow; release still needs a human zoom check.

Communicate the limits of rescue

Tell clients and juniors: extreme brightening can destroy information. Sometimes the right answer is a new scan or a better official copy.

Keep before/after on contested readings. Handle certified copies with particular restraint.

Team rule against over-processing

Prefer two moderate passes to one extreme. Mandatory spot checks on critical fields prevent unreadable “improved” packs.

Team rule against over-processing

Assistants under time pressure tend toward maximum filters. A rule of “prefer two moderate passes to one extreme” plus mandatory spot checks on critical fields prevents unreadable “improved” packs.

Before/after on contrast

On aggressive brightening, keep a before page and check digits and punctuation at 150% zoom. If commas or lines vanish, the filter was too strong - step back to a milder tier.

Local versus global filters

Lift contrast first on the affected zone (stamp field, dark corner) before filtering the whole page. Global filters often hit already-readable areas and destroy fine lines. Mark the zone briefly in the matter note if later audit is needed. Targeted rescue beats blanket aggression.

After contrast changes, compare file size: a sharp rise can signal unnecessary noise. Prefer a new scan to more filters. Size is then a quality indicator, not only a portal ceiling.

Clip warning on brightening

Watch for blown white areas after heavy brightening. Lines and punctuation disappear there. If whites “clip”, the filter was too strong - step back or rescan.

Record the decision and responsible person in one line on the matter note. That shortens queries and makes quality transferable across cover. Small notes beat long rework after a failed portal attempt. Matter anchor: content day 18.

Contrast rescues dark scans only up to the point where characters break. Gentle adjustments, checks on digits and tables and a new scan if needed beat aggressive filters. Readability is the goal, not the brightest-looking background.