Oh, thank you for looking at the problem.
200% enalargement definiely improved processing. My sample works perfectly now. But more testing detected a lot of similar images where processing fails. Eg
This is 200% enlarged image. OCR fails to recognise ‘91’ cell.
Looking further I processed image through Windows 10 Photo enhacement After this OCR perfectly extracted text from enhanced image. I made some research on C# Image processing. Looked at [https://blogs.msdn.microsoft.com/dotnet/2017/01/19/net-core-image-processing(https://blogs.msdn.microsoft.com/dotnet/2017/01/19/net-core-image-processing/) and tested MagicScaler. See image after MagicScaler processing below
Frankly I see no difference between 2 images but OCR API does Second image processed correctly.
I run dozens more tests with MagicScale processing all worked except one which I put below
This image is 200% enlarged by MagicScale. Last cell (‘6’) missed in OCR processing. May be you can suggest something about this.
I would be very grateful for the further ideas how improve OCR API text recognition.