Scanning Images

Scanning images should be a simple thing to do, but there are a few rules that you might want to follow when doing it.

First of all, some of the terms you should become familiar with when you are scanning:

  • dpi:  This stands for dots per inch and defines how many dots per inch of the image will be saved.  If you put 60 or 72 (a fairly common setting), you will get an image that looks all right but won’t enlarge very well.  The size of the saved image will also be relatively small.  If you had a 3″ by 5″ picture and you saved it at 72 dpi, then the total size of the image would be around 80,000 bytes.  This is good if you’re trying to save space on your computer, but not very good if you want to enlarge the image to show to people.300 dpi will make the image larger and it will look better if you’re going to print it.  Most printers print at 300 dpi, so saving at that size will give you an image that you know will print well at the same size as the original image.  But the file will be larger – about 1.3 megabytes.600 – 1200 dpi will give you a very large file to save, but it will also give you very good resolution is you want to enlarge the image to display it on a screen.  But beware, that 3″ x 5″ image scanned at 1200 dpi will take about 21 Megabytes of storage.
  • Cropping your images might also be something you want to do, especially if you’re trying to use face comparison software.  Lets say you have a picture with five people in it, but you only want to use the face of one person.  The best thing to do is scan the image at a very high resolution (1200 or 1600 dpi) and then crop out the face you want to compare.  There is software provided on Apple to do this call Preview, and on Windows called Paint.  On both systems there are many free programs that can also be used to crop images.Once you have scanned the image, crop the image so that just the face you want is the majority of the image.  It might look something like this:
    Now if you crop the image that you want, this is what the final image will look like:
    That may be enough to compare two faces, but in this case, it would have been better if the image was scanned at a higher resolution because the image would even be clearer.
  • Aspect Ratio:This is one of the most important factors in comparing images from photographs.  You have to be very careful not to change the aspect ratio of pictures, but unfortunately, some software programs will do it for you without your realizing it so that they can fit the photo is a definered space.  Be careful of this.  If you change the aspect ratio, then comparisons become meaningless, and you might ever make something look the same that isn’t, or something look different that is the same.  Here’s an example of how changing the aspect ration of the single picture above can make it look different.Look at the difference.  The face is narrower in the second picture, the head is longer and the eyes are closer together.  If you compared these two images – even though it’s the same person – the aspect ration might make it look like they are not.  Be careful with this.
  • Scanning Pictures from Newsprint.This is probably the most difficult thing to do because the pictures are made up of dots that are printed on paper, but at much less than the 300 dpi we are used to today.  The best thing to do is experiment until you get the picture that is the clearest.  Also, don’t scan in color, just scan black and white, and you’ll have better results.


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