[bksvol-discuss] How Grayscale works and why it can help (was Scanning Old Mass Market Paperbacks)

  • From: "Judy s." <cherryjam@xxxxxxxxxxxxxxxx>
  • To: bksvol-discuss@xxxxxxxxxxxxx
  • Date: Fri, 22 May 2009 01:01:00 -0500

I've been mulling over Roger's post because, as a sighted person, I realized after reading it that grayscale is another one of those concepts that is totally based on a visual experience.


I think I've come up with an analogy to help explain what grayscale does and why it helps to grayscale images when scanning books in situations like the old mass market paperbacks. So let me take a stab at it, and if this helps anyone out, great!

A scanner has to find a way to differentiate various parts of an image. When scanning text, it has to figure out what part of the page is text, and what part of the page is the paper background.

Suppose for a minute it's your job (and I'm assuming you are blind) to tell the difference between two different pieces of fruit, an apple and a pear. You have various characteristics of the apple and of the pear to help you out, including the shape of each, their smell, their texture, and their firmness. If your nose is completely plugged, however, you can't use the smell of the fruit or the taste to help you tell the difference. The apple and the pear will smell and taste just the same. If you focus your attention on trying to tell them apart based on those two characteristics, you're going to do a very poor job of it. The best thing to do is focus instead on the things you can distinguish, and perhaps find a way to make those differences between each even more distinctive. If you focus on the round shape of the apple and the distinctive shape of the pear, that would really help.

Now, here's how this relates to scanning text. As paper and ink age, their colors change. The human eye is much better at still seeing the contrast between the text and the background paper than a scanner is, so to a sighted person an aged page of text is still very readable. However, to the scanner the colors of the text and the background page can become too similar to easily distinguish one from the other. So the scanner now has to rely on something other than sharply distinct colors to help it out. This is where grayscaling an image comes in. Grayscaling removes the attribute of color, reducing all colors down to just black, white, and the shades of gray that lie in between, and thereby helps the scanner to focus just on the shapes of the letters.

The grayscaling helps make the shape of each letter in the text stand out to the scanner, just like focusing on the shape of the fruit can help you distinguish whether its an apple or a pear even when your nose is plugged.

Roger, here's an additional tidbit that might help (which only makes sense for someone like you who used to have full vision). Visually, if you could see it, the image a scanner creates when you tell it to grayscale something is like what you see when you take a color TV broadcast and watch it on a black and white TV. Everything isn't suddenly just pure black or pure white. It's black and white and all the shades of gray in between, which is where the term 'grayscale' comes from. smile.

Judy s.

Rogerbailey81@xxxxxxx wrote:
As much as I have learned on this list, my ignorance is about to show again. I don't know what greyscale is. I have seen it mentioned here on numerous occasions, but my impression was that it had something to do with Kursweil so I assumed it did not apply to me so I didn't pay much attention.

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