Getting a Better Scanned Image
I used a monochrome image so we could work mainly on brightness and contrast, and not have to worry about accurate color representation. So, how do we get a better image than the one on the last page? If I am doing this manually, I would take a test scan, and open the photo in my photo editing program to look at the brightness curve. The following is a screen shot of Picture Window, showing the original scan on the left, with its brightness histogram overlaid on top of the image (the right hand image is the scan discussed later on this page).
Again, the histogram in the brightness curve command simply shows the number of pixels which have a particular level of brightness, ranging from pure black (left hand side of the curve) to pure white (right hand side of the curve); the higher the peak, the more pixels have that level of brightness. As you can see in the curve, there is a huge peak at pure white, meaning much of the photo shows pure white. Since there is no variation in brightness in areas which are pure white, detail will be lost in those areas. Also, none of the pixels are darker than mid-grey. Looking at the curve above, if I were to adjust the scanning manually, I would rescan the photo with the brightness set lower (i.e. producing a darker scan), so that the curve would shift to the left, providing darker areas and fewer areas at pure white. If I had not gotten the curve all the way to black, and completely eliminated the pure white, I would then increase the contrast, to increase the number of brightness levels between the darkest and the brightest pixels in the image.
Since so much of the image is at the top brightness level, I could not create a good image despite my best manipulations with the brightness curve command.
So, since I did not want to do a lot of trial-and error scanning to get the proper settings, I used the scanning program I use for my slide/negative scanner, VueScan (Hamrick Software). This software allows you to set the white point and black point of the image, giving you much more control of the brightness and contrast in the scanned image. Some scanners come with programs that will allow you to do this, although of the scanner software that I have so far gotten with the scanners I have used, I have not found packages that are good at giving you this level of control. I understand that Silverfast, another 3rd party scanning program, is also quite good at these issues (though I have not used it).
VueScan gives you the following screen:
There are a few important points here. The program is set to automatically determine the white point (the point that is represented as pure white in the image) and the black point (same for pure black) in the image. The program will do this by finding the darkest pixels and setting the level to pure black, and the brightest 0.5% of pixels, and setting their level to pure white. Notice also that there is a setting for color balance, allowing several options for setting the overall color tone to the image. Not seen on the screen, but I set the scan for 24-bit color, and a 300 dpi scan. VueScan produced the following image:
The next page has a side-by-side comparison of the two scans, but note that this scan has a much broader range of brightness, and less posterization effect on the faces. The following shows the brightness curve for this scan (the right-hand image in the screen shot):
While it still does not use the full range, as you can see, much more of the brightness range is used, and much less of the image is pure white (which we see by the increase in detail in the bright areas compared to the original scan).
If we have a better starting scan, we can make a better final image.
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