How to discover the area chart data if we only have the image?

Question

The area chart (image) has a few data series, which are charted with different colors. We know the image size and co-ordinates of each lable on x-Axis, is it possible to discover the series of y-Axis by image recongition? Can anybody shed some light?

Answer 1

If you know the y-axis scale, it should be possible.

To screenscrape, you could first filter your image with a color filter for each of the series. Second step would be to gather the coordinates of all remaining pixels in your temporary image and transform them these to the scale needed.

given

• a pixel at coordinates x,y
• the offset of the charts Origin in image pixels xoffset, yoffset
• the Scale of you chart axis xscale, yscale

you could calculate the data for this pixel (pseudocode)

pixelData.x := (x - xoffset) * xscale
pixeldata.y := (y - yoffset) * yscale

And afterwards, do some interpolation if your series line is more then one pixel wide (for example get the average data for all pixels in a single column or so).

Update1: Pseudocode for naive color filter filtering out red charts

//set up desired color levels to filter out
redmin := 240;
redmax := 255
bluemin := 0;
bluemax := 0;
greenmin := 0
greenmax := 0;

//load source bitmap
myBitmap := LoadBitmap("Chartfile.bmp");

//loop over bitmap pixels
for iX := 0 to myBitmap.width-1 do
  for iY := 0 myBitmap.height-1 do
    begin  
      myColorVal := myBitmap.GetPixels(iX, iY);
      //if the pixel color is inside your target color range, store it
      if ((mycolorVal.r >=redmin) and (myColorVal.r <= redmax)) and
         ((mycolorVal.g >=greenmin) and (myColorVal.g <= greenmax)) and
         ((mycolorVal.b >=bluemin) and (myColorVal.b <= bluemax)) then 
         storeDataValue(iX, iY); //performs the value scaling operation mentioned above
    end;