Saturday, September 05, 2009

Lifting fingerprints

Fingerprints pose challenges to restoration.  Above is a photograph of Honus Wagner, circa 1911, which is available in a 55MB digitized file from the Library of Congress.  It is a pleasure to see institutions provide such high quality copies, yet with material of this age the odds are pretty good that someone has been sloppy about handling the document.  In this instance  the biggest problem is a fingerprint beside the right elbow.

Getting in a bit closer reveals what a difficult issue this is: the fingerprint whorls are roughly perpendicular to the seams and creases of Wagner's uniform and they continue past his uniform to the grass behind him.

What we want to do is retain the meaningful data while getting rid of the fingerprint.  A lazy approach would be to remove the brightest fingerprint highlights.  That won't be good enough: the human brain is excellent at pattern recognition.  Subtle sets of parallel lines will still be apparent.  So it's going to be necessary to recreate the pinstripes on the sleeve, the creases on the pants leg, and the relevant shadows.

Whenever a restoration task seems daunting a good approach is to do the easiest part first.  A little time and familiarity makes it simpler to work out the rest.  So we'll start at far right.  I used the Photoshop healing brush tool at 100% hardness and 9 pixels.  An important trick to getting good results is to change the source sampling point frequently.

Moving left to the edge of the leg, the healing brush becomes more tricky.  The tool's algorithm draws data from outside the selection area, which tends to smudge borders.  Most people switch to the clone stamp in this type of situation.  I recommend around 35% hardness for clone stamping in most restorations, including this one.  The reduced hardness usually avoids the cookie-cutter appearance of novice image editing.

Editors who are more ambitious could try what I did here: it is possible to use the healing brush effectively at borders if the source area and destination area are close matches.  I reset the tool diameter to 5 pixels and sampled from a border section lower on the leg, then applied the tool to the fingerprint marks at the edge of the bright area.  The advantage of this approach is that when it works it yields a very good blend.  If the results aren't desirable at the first attempt, just back out through the history and start again.

Although the clone stamp tool is good for restoration at low hardness, I nearly always keep the healing brush set to 100% hardness.  Anything less gives muddy results.  Here's how the area appears after a few minutes' work.

Now it's time to handle the toughest sections.  Most of the work on this photograph has been done at 200% resolution.  For this part we'll go in at 300% resolution and use both the clone stamp and the healing brush.  The aim is to infer meaningful data about the arm, elbow, shadows, and uniform from the areas that haven't been marred by the fingerprint.  The results won't be perfectly sharp because the photo is no longer sharp at such high resolution.  Part of the goal is to generate a slightly mottled appearance that looks compatible with undamaged areas elsewhere in the photograph.

There's the result at high resolution. Now we'll pull out and see how this blends with the surrounding area.

This is not a complete restoration, just a partial screenshot of the image as it exists on my computer as of this writing.  The fingerprint itself was rather large and this demonstration didn't erase all of it.  Notice the subtle grooves above and below the area that was worked on?  That's what I meant about the human brain being an excellent at pattern recognition.  Other parts of the fingerprint still remain.  This work goes more slowly than ordinary scratch and dirt removal.

Fingerprints are chemically interesting.  From a preservation standpoint that means there's a strong likelihood that oils and dirt will cause chemical reactions on a photographic print.  Those changes can't be brushed or washed away.  Attempts at cleaning often cause additional damage.  When you need to scan a damaged print, might as well leave bad enough alone on the physical item and correct the problem digitally.

So if you have a family member with bad habits at handling old prints, sit them down and show them this post.  Better yet, fire up an image editing program and task them with cleaning up their own mess.  Whether the goal is to preserve baseball history or family memories, it's much less effort to wash one's hands and hold photographic prints by the edges.

1 comment:

Special Offers said...

Wow this is a really great blog. I've always been fascinated with restoration and techniques. Thanks for the great content!