Noise removal

Dirt, spots, scratches, glare, unwanted gradients, and other noise are a common problem when scanning low-quality sources such as newspapers or old books, or when taking photographs. These image defects can interfere with recognition, significantly reduce the accuracy of OCR, and may cause spots to be misrecognised as characters.

Aspose.OCR provides automated processing algorithms that remove noise from images before proceeding to recognition.

Noise removal automatically converts the image to black and white.

Automatic noise removal

To automatically remove the noise from the image before recognition, run the image through OCR_IMG_PREPROCESS_AUTODENOISING preprocessing filter or enable auto_denoising property in recognition settings.

Preprocessing filter

std::string image_path = "source.png";
custom_preprocessing_filters filters_;
filters_.filter_1 = OCR_IMG_PREPROCESS_AUTODENOISING;
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_denoising = true;
size_t res_len = aspose::ocr::page_settings(image_path.c_str(), buffer, len, settings);
std::wcout << buffer;

Usage scenarios

Automatic noise removal is recommended for the following images:

• Photos, especially those taken in low light conditions.
• Old books.
• Newspapers.
• Postcards.
• Text with a photo or picture as a background.
• Scanned papers with spots and dirt.

However, noise removal can reduce recognition accuracy when working with poor-quality prints, as it can lead to the loss of important details, such as light punctuation or heavily fragmented characters.