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I sent an image. Why didn't you use it?
I receive many so-called "high-resolution" images from from contributors. Unfortunately, some are unusable because of scanning problems.
Before I explain some of the most common problems, I want to stress that I GENUINELY APPRECIATE everyone's help and input! And I desperately want to avoid hurting anyone's feelings. There are, however, certain realities that affect what I can and cannot use.
If I did not use an image of a certificate you sent, then your image probably showed one or more of the following typical problems.
Uneven exposure. If a scan is lighter or darker in strips, I will reject the image for use as a high resolution image.
This kind of problem is VERY common because scanner bulbs age over time. They gradually grow dimmer and darker in spots. When that happens, scans show streaky appearances. I can fix some of those problems, but it is time-consuming.
Light edges or corners. If opposite corners of scans don't look the same, there was probably light leakage at the time of scanning. This is usually caused by the cover not being tight against the paper all the way around. If one corner is unusually light, then the image is probably not usable. Again, I can often fix some, but certainly not all, problems.
Overly dark images. Dark images are often caused by bulbs going bad. I can fix most dark images, but some are too far gone. Dark images are always better than light images.
Light images. In general, if an image is too light, I must reject it for as a high resolution image. I advise turning off off auto-exposure and experimenting with different settings.
How do you know if an image is too light? Most certificate paper is ivory to light tan. If you cannot see paper color in your scans, the scan is too light. Fortunately, even entry level scanners have exposure adjustments that will take care of that problem.
Contrasty images. Contrast is the difference between light and dark areas of a certificate. I can always add contrast to certificates that look gray, but I cannot remove contrast without ruining overall appearance. Read more here.
In this example, notice how 'Reading Company' seems to jump from the screen. That is clear evidence of overly high contrast.
Poor color. When scanner bulbs age, they usually stop create transmitting even spectrums of white light. Consequently, their ability to reproduce colors diminishes. Scans often show sickly brown or greenish color casts. I can remove some color casts, but that often exposes additional, hidden problems.
Low resolution. The rule of thumb is, that if you cannot read the printer's name, then the image resolution is too low.
Many people think they are sending high resolution images, when, in fact, they are not. If a certificate is reduced during scanning, then it is NOT a high-resolution image. Read about the problem.
Over sharpening. Software included with most entry-level scanners has sharpening turned on by default.
Sharpening is good for typed documents and improves many ordinary photographs. Sharpening rarely improves certificates. Images can be often used if sharpening is set at a low level or if the scans are over 300 dpi. Note how 'Reading Company' looks abnormal relative to the rest of the certificate. Read more here.
Images from cameras. Images from digital camera images usually have too many problems to fix in five minutes. Almost every photograph shows uneven exposure and lens distortion. While I can fix both problems, it usually takes too much time.
Edges cut off. Unless a certificate is really rare, I only use images of complete certificates. Some partial images persist in the online database simply because I have never been able to remove all problem images. Please help me replace bad images. (Note how the left edge of this example is cut off.)
Many collectors start out with lower-price, entry-level scanners. Many quickly discover their certificates, even ordinary stock certificates, are too large for their device. They can still make good images by scanning larger certificates in two or more pieces with at least 2 inches of overlap. See Scanning Large Certificates for more information.
I can easily patch scans of partial certificates back together into whole images as long as the pieces don't have other problems. There are three common mistakes, however, that cause me to reject such scans.
Lack of sufficient overlap. I cannot patch pieces together if there is insufficient overlap. 2" overlap is usually ideal.
This example shows about 0.3" of underlap.
Rotating certificates between scans. Certificates scanned in pieces should be scanned with the top facing the same direction for each piece. If rotated between scans, colors and exposure ALWAYS end up different between the pieces. That makes them terribly difficult to patch together.
Yes, some people try to trick me by rotating one of the images before they send them to me. Rotation between scans almost always leaves evidence.
Pieces scanned at different scales. This problem happens frequently. I suspect people are unknowingly reducing their images and can't control it. Patching these kinds of images together is almost never worth the time because the pixels are different sizes and will never match.
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