Contrast correction

Low contrast and blurring are the most typical distortions when text is photographed with a smartphone camera, especially in low light conditions. They make it difficult for the OCR algorithms to operate successfully, significantly reducing the recognition accuracy.

Aspose.OCR can automatically increase the contrast of images before proceeding to recognition.

Contrast correction automatically converts the image to black and white.

Automatic contrast adjustments

To automatically increase the image contrast before recognition, run the image through OCR_IMG_PREPROCESS_CONTRAST_CORRECTION preprocessing filter or enable auto_contrast property in recognition settings.

Preprocessing filter

std::string image_path = "source.png";
custom_preprocessing_filters filters_;
filters_.filter_1 = OCR_IMG_PREPROCESS_CONTRAST_CORRECTION;
asposeocr_preprocess_page_and_save(image_path.c_str(), "result.png", filters_);

Recognition settings

std::string image_path = "source.png";
const size_t len = 4096;
wchar_t buffer[len] = { 0 };
RecognitionSettings settings;
settings.auto_contrast = true;
size_t res_len = aspose::ocr::page_settings(image_path.c_str(), buffer, len, settings);
std::wcout << buffer;

Usage scenarios

Automatic contrast adjustment is recommended for the following images:

• Photos, especially those taken in low light conditions without optical or digital image stabilization.
• Old papers.
• Text on a background.