How to process multiple images at once

Question

I'm trying to extract some text from an image using tesseract, and I've noticed if I divide the image to 9 smaller pieces the system is more accurate, so what I'm trying to accomplish is to process all 9 images at once (parallel) and this is the way I wanted to do it:

private static int GetImageText(Image src)
{
    string[] words = { words-to-check };
    List<string> found = new();
    string path = Environment.CurrentDirectory;
    try
    {
        using (var engine = new TesseractEngine(path, "eng", EngineMode.LstmOnly))
        {
            Parallel.ForEach(CutUpImage(src), (img) =>
            {
                using (var ms = new MemoryStream())
                {
                    img.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                    using (var loadedImg = Pix.LoadFromMemory(ms.ToArray()))
                    using (var page = engine.Process(loadedImg))
                    {
                       var c = page.GetText();
                       foreach (var word in words) if (c.Contains(word)) found.Add(word);
                    }
                }
            });
            return found.Count;
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

but I'm getting an error (Only one image can be processed at once. Please make sure you dispose of the page once your finished with it.).

So I had to move the new TesseractEngine into the loop like this:

private static int GetImageText(Image src)
{
    string[] words = { words-to-check };
    List<string> found = new();
    string path = Environment.CurrentDirectory;
    Parallel.ForEach(CutUpImage(src), (img) =>
    {
        using (var engine = new TesseractEngine(path, "eng", EngineMode.LstmOnly))
        {
            using (var ms = new MemoryStream())
            {
                img.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                using (var loadedImg = Pix.LoadFromMemory(ms.ToArray()))
                using (var page = engine.Process(loadedImg))
                {
                    var c = page.GetText();
                    foreach (var word in words) if (c.Contains(word)) found.Add(word);
                }
            }
        }
    });
    return found.Count;
}

but then it takes a full minute to finish processing all images.

so my question is how do I make the new TesseractEngine work outside the loop, and more generally how do I make this work faster?

Answer 1

ok so the solution to my problem is simple... don't use parallel processing!

I switched the Parallel.ForEach to a traditional foreach (idk why I decided to try parallel processing first...) and it now takes 12 seconds to process them all, the reason it took a minute is most probably to spin up the actual engine... this is the code :

private static int GetImageText(Image src)
{
    string[] words = { words-to-check };
    List<string> found = new();
    string path = Environment.CurrentDirectory;

    using (var engine = new TesseractEngine(path, "eng", EngineMode.LstmOnly))
    using (var ms = new MemoryStream())
        foreach (var img in CutUpImage(src))
        {
            img.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            using (var loadedImg = Pix.LoadFromMemory(ms.ToArray()))
            using (var page = engine.Process(loadedImg))
            {
                var c = page.GetText();
                foreach (var word in words) if (c.Contains(word)) found.Add(word);
            }
            ms.SetLength(0);
        }
    return found.Count;
}

p.s. this is the CutUpImage code if someone ever wants to use it...

private static Image[] CutUpImage(Image src)
{
    int widthThird = (int)((double)src.Width / 3.0 + 0.5);
    int heightThird = (int)((double)src.Height / 3.0 + 0.5);
    var imgarray = new Image[9];
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++)
        {
            var index = i*3+j;
            imgarray[index] = new Bitmap(widthThird, heightThird);
            Graphics g = Graphics.FromImage(imgarray[index]);
            g.DrawImage(src, new Rectangle(0, 0, widthThird, heightThird),
                new Rectangle(j * widthThird, i * heightThird, widthThird, heightThird), 
                GraphicsUnit.Pixel);

            g.Dispose();
        }
    return imgarray;
}