I picked up a stack of 1950s travel posters at an estate sale last month for almost nothing. They were stained, foxed, and one had what I am fairly sure is forty years of cooking grease on the corner. The obvious move is to scan them and run a conversion pass to get them looking sharp for printing.
The first attempt was terrible. Every pass made the damage louder. Dust turned into bright speckles, the fold lines became hard black bands, and the whole thing looked like a photocopy of a photocopy. The problem was not the conversion. It was that I gave it a dirty source. Here is the prep routine that fixed it, using imagetoimage.cn for the actual conversion pass.
Scan Bigger Than You Think You Need
Scan at 600dpi minimum, even if you only want a 300dpi print. The extra resolution is not for the final output, it is so the prep steps have enough pixels to work with. Removing dust from a 300dpi scan eats detail. Removing it from a 600dpi scan is easy.
Scan as TIFF if your scanner allows it. JPEG compression around fine paper texture creates blocky artefacts that a conversion pass will happily interpret as intentional detail, and you will spend an hour trying to figure out where the ugly pattern came from.
Fix the Paper Tone Before Anything Else
Old paper is yellow, and everything downstream inherits that cast. Use a white balance picker on a part of the scan that was originally white, ideally a margin or the reverse side bleed. Do this on a duplicate layer so you can dial it back. Full correction often looks clinical, and something around 80% usually reads better.
Watch for uneven tone across the sheet. Fluorescent lights and phone cameras create a colour gradient that white balance cannot fix, because the correct temperature is different on each side. If you see it, apply a gentle gradient correction rather than a global one.
Deal With Dust at the Source
Compressed air and a microfibre cloth before scanning remove about 90% of the speckles. Cleaning the scan afterwards is slower and always loses something. If the poster is fragile, do not press it flat under glass, because you risk cracking ink along the fold lines.
For the remaining dust, a manual spot heal at high zoom beats any automatic filter. Automatic dust removal cannot tell the difference between a speck and a highlight in the artwork, and on painted surfaces it produces a slightly waxy, smeared look that is very hard to spot until you print.
Handle Folds and Creases Separately
Do not try to remove fold lines entirely. On a poster that has been folded in quarters for seventy years, the crease has caused real ink loss and paper damage. If you flatten it completely the surface reads as plastic.
Instead, reduce the contrast of the crease rather than erasing it. Use a soft lighten pass along the fold at low opacity, and leave the structural line. The goal is a poster that looks cared for, not one that looks like it was printed yesterday.
Now Run the Conversion Pass
With a clean, correctly toned scan, the conversion behaves completely differently. Dust does not get amplified. Colours do not shift into muddy territory. The tool has a clear original to work from instead of guessing at what the artwork was supposed to look like.
Keep the strength moderate. Vintage poster art has flat ink fields and limited palettes, and a heavy pass will start inventing gradients and texture that were never there. If your tool has a content-versus-strength control, bias toward preserving content. You want the original drawing intact and only the surface treatment updated.
Compare Against the Original Constantly
Keep the source scan open in a second window the entire time. It is very easy to drift, and after twenty minutes of adjustments you will have a technically cleaner image that has lost the specific colour character that made the poster worth buying.
The test is simple. Put both side by side at the same size and look away for a moment, then look back. Whatever draws your eye first is usually the one with more life, and it is usually the original.
The whole prep routine adds maybe fifteen minutes per poster, and it is the difference between a file you can sell and a file you quietly delete. Once the source is clean, the pass at imagetoimage.cn takes a minute and the results hold up at print size. Fix the scan first, and everything after that is easy.