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How does pixel counting work? How do you reverse engineer a chart?
This is a serious question. I'm new here.
I think this is fantastic that people do this. Just link me to a post that explains it or something. Thanks.
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First of all, it's based on the assumption the chart is in a proper scale.
In the image below, 400000 units are represented in 170 pixels, so each pixel = 400000/170 = 2353 units.
Then, you count how many pixels each data point has. For instance, Wii U's 3rd week has 28 pixels. Since you know how much each pixel is, you do 28 * 2353 = 65882 units.
It's obviously, far from perfect. The first thing you'll notice is that in the example the best you can guess is within 2.3k units jumps, so if the number is exactly 3.9k, you won't really know -- you'll be between 2.3k and 4.6k. JPEG images, blurry as the Nintendo ones, not to mention the usage of thick lines, makes thing all the more uncertain.
There are software that do this automatically (you can find some if you google for extract data from chart or graph). You can also use measurements other than pixels.
I've always done it using GIMP and a spreadsheet, but I'm trying using ImageJ to do this now. First time, so be gentle. Anyone has tips, please suggest them.
http://rsbweb.nih.gov/ij/
I used the line tool to measure the vertical axis and used that length to set a scale. Then I used the line tool to measure from the bottom of the graph up to each point along each curve, and used Ctrl+M to measure the length of the line. (Hold shift while using line tool to keep it at a 90° angle to the horizontal axis.) These get recorded in a side window and you then export those results and import into a spreadsheet if you need to manipulate them into a graph or something...
I do it manually too (but with Paint, borderline masochism).
I tried using some programs before but they were sort of complicated and/or I didn't really like the results. Will try that one some day.
