Forensics Tutorial
The forensics ability of Focus Magic has been used by intelligence agencies, the military and law enforcement around the world.
It can recover detail from images that is not visible to the naked eye and has been used in multiple court cases including murder trials. For court cases we have been asked how Focus Magic works so that the jury is happy that the image has not been “doctored” and is valid as evidence.
Example 1 - Out of Focus Blur
Detail can be recovered because each pixel becomes a circle which overlaps the other pixel circles.
The overlapping is done to a formula, so reversing the formula can recover a fair amount of detail.
For details to be recovered, the Blur Width needs to be at least 5 pixels.
Example 2 - Motion Blur
Example 2 - Motion Blur
Detail can be recovered because each pixel becomes a line which overlaps the other pixel lines. The overlapping is done to a formula, so reversing the formula can recover a fair amount of detail.
In this case the After image is noisy because we set the Remove Noise setting to None in order to recover the most detail.
For details to be recovered, the Blur Distance needs to be at least 7 pixels.
Example 3 - Resolution Blur
Example 3 - Resolution Blur
For this license plate “RSJ 9594”, the numbers are about ten pixels high, so we can recover a tiny bit of information. If the the numbers are ony a few pixels high then no detail can be recovered.
A Note About Scanned Photos
For scanned photos, scan them in using a resolution which is high enough to have a blur width between 10 and 20. If for example the photo was scanned in at 1200 bpi (bits per inch), and the blur width is 6, then scan it in again using 2400 bpi so that you can use a blur width of 12. If the image was scanned in at its highest resolution then increase the image size as for a digital camera (next). Not all scanners produce sharp scans. If you are scanning in an image with quite a low blur width, it is vital to use a good scanner which doesn’t contribute to the blur of the image. After scanning the image in, compare the real image with what you see on the screen and make sure that it hasn’t contributed any blur to the image. If you have the negative of the photo, then you could make a large print of the photo before scanning it in. Make sure that the photo lab understands the importance of getting a sharp image.
If the photo is from a digital camera, then increase the image size so that the blur width is in the 10 to 20 range. It is probably best to increase the file size by a factor of 2 or 4 so that the interpolation is kept as simple and hence as accurate as possible.
If the blur width is greater than 20 then scale the image down so that the blur width is in the 10 to 20 range. Focus Magic can process a maximum blur width of 20. If it could go above 20 then you wouldn’t gain much (or anything) anyway.
The Effect of Noise
A grainy image won’t focus as well as a smooth clean image.
Image with a normal amount of noise (grain).
Noise (10 % uniform noise using Photoshop) was added to simulate a grainy image. The re-focusing is not nearly as good.
If you already have an image, there may not be a lot you can do to remove noise or grain. If you have a negative, you might be able to reduce the noise by developing the print again using better equipment. If the image has dust on it, then you can gently wipe the dust off.
