How to remove (some) yellow
The most common problem I see
In a normal year, I catalog between 7,000 and 9,000 images. A large percentage of those images have a yellow tint. Some are downright awful.
- certificates themselves
- the majority of papers used to print certificates had a light yellow coloration
- thin paper
- source light
- photographing certificates under incandescent lights
- photographing certificates with insufficient light
- photographing certificates in rooms lit by early morning or late afternoon sun
- sun exposure
- aged paper, particularly the pulp paper used for many generic certificates (this applies to many framed or previously framed certificates)
- uncalibrated scanners
- aged scanners
- a combination of thin paper and yellowish tint
It is not going to be possible to eliminate all yellowed images because so many certificates have a natural light yellow tint. Anyone who objects to that assessment simply needs to test by placing several of the whitest certificates in possession against ordinary "bright white" copy paper.
- Keep certificates away from sunlight. This is especially recommended for generic certificates printed on pulp paper.
- Avoid framing genuine certificates. Use printed copies.
- Be aware of time of day. Photograph certificates around mid-day if using a camera anywhere near sunlit windows.
- Use a flash if photographing certificates in conditions of insufficient light or under incandescent lights. (Be aware of fluorescent lights, too, because they impart greenish tints.)
- Remove yellowish tints with photo editing software.
What is your intended use?
- Personal records? Image quality and odd tints may not matter.
- Appraisals for insurance or tax purposes? Quality might matter, possibly a lot. You might need appraisals after an insurable loss of your collection. You may be required to send images as proof of your collection to someone you may never see your certificates in person. The IRS will almost certainly require appraisals when taking deductions for donations to historical societies and museums.
- Inspections prior to selling through auction houses? Major houses are going to want to see your certificates or at least good images before committing to sell your material. I imagine that collectors would want to present their holdings in the best possible manner.
- Sales on eBay? Yes, it is true that sellers can sell anything on eBay if the price is right. But that does NOT mean sellers will achieve the highest possible bids by using junk images. I know that many sellers are satisfied with whatever they receive. They may not know that I am the guy who records prices every day and I am the guy who KNOWS that the majority of amateur sellers are "leaving money on the table." Small and terrible images might sell, but (statistically) good images sell better.
Why are scanned images often yellow?
Now we are getting down to the nitty gritty. You will notice I did not say one of the remedies was to buy a scanner. Scanners are great at reproducing accurately-scaled and highly-detailed images, BUT they don't always do a great job reproducing 100% accurate colors with certificates.
It turns out that stocks, bonds and related documents present scanners with a yellow witch's brew created by two innocent-seeming qualities:
- certificates tend to be thin
- certificates usually have a slight yellowish tint
Here is an illustration of three scans created within 90 seconds of each other on an HP477 Color LaserJet Pro scanner with the exact same settings. The scanner bulb has been used for fewer than 300 scans. At left is a 4-page George H. LaBarre catalog printed on very white paper. The image in the center is an untouched scan of a certificate just as it was saved by the scanner. The image on the right is the same certificate scanned with a piece of light gray posterboard placed between the certificate and the scanner cover.
By comparison to LaBarre's catalog, the yellow in the certificate in the center is quite obvious and unappealing. The same certificate on the right looks much more realistic.
The real problem is light from the scanner bulb penetrated the certificate, bounced off the scanner cover and penetrated the certificate again before light was recorded by the scanner. The slight natural ivory color reflected from the paper was combined with light that passed through the paper twice, making the scan look much worse than real life. The light gray posterboard used in the righthand example diminished reflectance from the scanner cover and removed almost all of the unattractive yellow except what was already in the paper.
These examples and many others prove that:
- we will definitely encounter problems scanning thin certificates
- we can diminish some of those problems by limiting reflectance off scanner covers.
How thin is thin?
A certificate is thin enough to cause yellowing problems if we can easily see text on the back or from another document placed underneath. This is called show-through and is quite evident in the stock certificates shown above.
The Penn Central stock certificate below is sufficiently thick to avoid problems even though the paper has a slight ivory tint and there is text on the back. When compared to George's catalog, the barest hint of yellow is visible, but it is no more obvious in the scan than on the certificate itself.
The easiest remedy
Awareness is the first step in preventing yellow from appearing in scanned or photographed images of certificates. With that in mind:
- Use adequate light when photographing certificates.
- Place a piece of light gray, light blue or black posterboard between certificates and scanner covers when scanning. (See more hints in my section on show-through and yellowing.)
- Replace scanner bulbs (if possible) when scanners begin imparting their own colors or dark bands.
Awareness and attempts at prevention cannot keep all unwanted colors and problems out of images of certificates. Photo editing software, however, can correct many problems after the fact. To that end, I have prepared several tutorials focused strictly on modifying images of certificates. See links to all tutorials at Image manipulation.