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How to invert an image for better recognition?
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PataAndrey  
#1 Posted : Sunday, November 5, 2017 1:34:08 AM(UTC)
PataAndrey

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Joined: 11/3/2017(UTC)
Posts: 7

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Question
I have an image with quite clear text on it, but OCR have a lot of false positives. For example:

It read 6 as 5
D as 0
E as £
B as 3
8 as S

I need to have recognised the second line (1 A0 D5 …)

image001.png (3kb) downloaded 30 time(s).

Answer
For best recognition, it is best to use pictures with black text on a white background. Therefore, you need to invert the image as follows:

image002.png (4kb) downloaded 30 time(s).

Using the following code, you can invert the image.
Code:

Image pix = Image.FromFile(@"C:\image001.png");
Bitmap mybitmap = new Bitmap(pix);
for (int x = 0; x < pix.Width; x++)
{
    for (int y = 0; y < pix.Height; y++)
    {
        Color mypixel = mybitmap.GetPixel(x, y);
        mybitmap.SetPixel(x, y, Color.FromArgb(mypixel.A, 0xFF - mypixel.R, 0xFF - mypixel.G, 0xFF - mypixel.B));
    }
}


After all you can use the GetTextFromImage method to find the text you need. In this case, we read a second line:

Code:

using (var api = OcrApi.Create())
{
    api.Init(Patagames.Ocr.Enums.Languages.English, null, Patagames.Ocr.Enums.OcrEngineMode.OEM_CUBE_ONLY);
    using (var img = OcrPix.FromBitmap(mybitmap))
    {
        string str = api.GetTextFromImage(img, new Point(20,30), new Size(350, 30));
        MessageBox.Show(str.ToUpper());
    }
}

Edited by user Monday, November 6, 2017 4:28:52 AM(UTC)  | Reason: Not specified
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