Some tech notes on digital ghost photography


by Leon Baker, Tech Specialist


Why can't we see ghosts but some strange things show up in my digital photos?

The average human eye can see wavelengths of 380-700nm, that's like 1/3 to 1/7 of a millimeter, so pretty short and fast. Some people with Aphakia have no lens, which filters the light to only allow the visible spectrum in, and can see well into the UV spectrum, although without a lens they can't focus. Digital cameras use a wide variety of technologies to save an image as an EXIF or JPEG file, but the general process is the same. All electromagnetic frequencies hit the lens, but the actual photocell can recognize only the 1000nm-450nm range. As you can see, that is offset from the human eye, more towards the IR range. That mirrory piece of glass over the lens filters some of the non-visible light spectrum, so the pictures don't look weird. So, some IR light, that we can't see, is saved by the camera and then is processed with a "gamma curve" program, which blends the contrasting colors at the edges. Then a "tonal reproduction" program boosts the contrast (kinda working against each other). Then there is the "low pass filtering" which moves the invisible light frequency in to a visible frequency. That's called "aliasing". And that's why we can see them on the camera. As some of you may have noticed, this summer the basements were hot. That heat causes the photocell to bleed over and cause blotchy photos in the low light conditions, causing a lot of pareidolia, or matrixing when we look at the photos. That low pass filtering removes most of the "noise" causing posterization or large, square pixels, in the photos.


Why can't you see that full body apparition on Facebook, but it is right here on my computer screen?

Well, Facebook compresses the uploaded photos up to 80%, shaving off some of the colors, aliasing them to the nearest colors. Those sharp, purple lines are now victim to Facebook's own low pass filter, gamma curve filter, and whatever else they use. Now all that is visible is a posterized, blotchy, dark photo as you proudly proclamation that you have irrefutable proof that ghosts exist, and everyone proclaims that they have irrefutable proof that you are nuts! So, in a nutshell, the invisible IR light where the ghost has posed so proudly is translated into a visible, although fuzzy, image on your camera. And Facebook compresses him back into oblivion.


 Tech note on pets

by Leon Baker, Tech Specialist


Some people believe that their animals "see ghosts" in their homes, especially when their dog suddenly stands and starts barking at the door or wall, or their cat suddenly takes an interest in something we can't see. Of course we assume there is another intelligent "person" in the area, and that is natural. Humans are not natural hunters, we are more gatherers, and our survival instincts are high, therefore we are not natural food sources, either. Our minds naturally assume that there is a threat and we prepare accordingly. Dogs and cats are designed as predators, with acute senses much greater than our own, however not as finely tuned in the vision area. Humans can see in a spectrum of 380nm (UV) to around 700nm (IR), while dogs and cats have a more segmented color spectrum. Tests have proven that they DO see in color, but not as well as humans. They are pretty much red/green color blind and cats can't differentiate different shades of red. They actually see less as the wavelength gets closer to the Infrared (IR) spectrum. Tests have shown that no known animal can see IR with their eyes, the rods and cones common to most invertebrates being almost identical in design and sensitivity. What is different, however, is the structure of the eyes as a whole. Dogs and cats have larger pupils, which are able to dilate to around 90% of the iris. This allows more light to enter the eye. Add to that, the Tapetum Lucidum, the reflective membrane at the back of the eyes that make them look like zombies when you shine a light at them. This membrane reflects light towards the ocular receptors, the rods and cones. With these features dogs and cats are able to see in 1/6-1/7th of the light we can, even when it looks completely dark to us. But their vision is not as sharp as ours. There is only so much room in their eyes for rods and cones at their focal point, and they have more rods (which sense light) than we do, and fewer cones (which sense color). But what do they see that we can't when they are so attentive to that part of the room? Well, maybe they aren't seeing anything. Along with acute night vision they also have very sensitive hearing. They don't blast their radios while they drive and when is the last time you saw rover with ear buds? Their whiskers are also sense organs. Maybe what they are sensing is a sound, or a vibration. So in conclusion, your pets don't "see" anything you can't see. But they might just sense something, which may be even more disturbing. They can't tell us what they see anyway. Just rest assured, something is probably there, even if it's just a mouse in the wall.