tesseract-rs

The OcrEngineMode enum allows you to control which Tesseract engine is used:

• Default: Run Tesseract only (fastest, but deprecated).
• LstmOnly: Run just the LSTM line recognizer.
• TesseractLstmCombined: Run the LSTM recognizer with fallback to Tesseract (deprecated).
• TesseractOnly: Automatically infer mode from config or default to OEM_TESSERACT_ONLY.

```rust
use tesseract::{Tesseract, OcrEngineMode};

let mut tess = Tesseract::new_with_oem(
    None,
    Some("eng"),
    OcrEngineMode::LstmOnly
)?;

Use Tesseract::new or Tesseract::new_with_oem to create a new OCR engine instance. You can optionally specify a datapath (the path to training data) and a language (e.g., "eng").

If you need to specify the OCR Engine Mode (OEM), use new_with_oem with an OcrEngineMode value.

```rust
// Basic initialization
let mut tess = Tesseract::new(Some("/path/to/data"), Some("eng"))?;

// Initialization with specific OCR Engine Mode
let mut tess = Tesseract::new_with_oem(
    None,
    Some("eng"),
    OcrEngineMode::LstmOnly
)?;

If you are working with low-level bindings or need the raw Tesseract value, use the as_tess_page_seg_mode() method on a PageSegMode instance. This returns the underlying TessPageSegMode type used by the Tesseract C API.

let mode = PageSegMode::PsmSingleBlock;
let tess_mode = mode.as_tess_page_seg_mode();

The Tesseract struct provides several methods to provide image data to the engine:

• set_image(filename: &str): Loads an image from a file path.
• set_image_from_mem(img: &[u8]): Loads an image from a byte slice in memory.
• set_frame(frame_data: &[u8], width: i32, height: i32, bytes_per_pixel: i32, bytes_per_line: i32): Sets an image from raw frame data (useful for video frames).

Note that these methods consume and return self, allowing for a builder-like pattern.

```rust
// From file
tess.set_image("path/to/image.png")?;

// From memory
tess.set_image_from_mem(&buffer)?;

// From raw frame
tess.set_frame(data, 1920, 1080, 4, 1920 * 4)?;

For simple tasks, use the convenience functions that wrap the entire lifecycle (init -> set image -> recognize -> get text):

• ocr(filename: &str, language: &str): Performs OCR on a file.
• ocr_from_frame(frame_data, width, height, bytes_per_pixel, bytes_per_line, language): Performs OCR on raw frame data.

// Simple file OCR
let text = ocr("image.png", "eng")?;

// Frame OCR
let text = ocr_from_frame(&data, 800, 600, 3, 2400, "eng")?;

To extract text from an image, you must first call .recognize() to process the image, then call a getter method to retrieve the results.

Available extraction methods:

• get_text(): Returns the recognized text as a String.
• get_hocr_text(page: i32): Returns text encoded as HTML with bounding box tags.
• get_tsv_text(page: i32): Returns text encoded as TSV, including bounding boxes and confidence scores.

You can also check the overall confidence using mean_text_conf().

let text = Tesseract::new(None, Some("eng"))?
    .set_image("image.png")?
    .recognize()?
    .get_text()?;

println!("Recognized text: {}", text);

You can fine-tune the OCR process using the following methods:

• set_variable(name: &str, value: &str): Sets a Tesseract configuration variable (e.g., tessedit_char_blacklist).
• set_page_seg_mode(mode: PageSegMode): Sets the page segmentation mode.
• set_rectangle(left, top, width, height): Limits OCR to a specific rectangular area of the image.
• set_source_resolution(ppi: i32): Sets the source image resolution in PPI.

tess.set_variable("tessedit_char_blacklist", "0123456789")?;
tess.set_page_seg_mode(PageSegMode::SingleColumn);
tess.set_rectangle(0, 0, 100, 100);
tess.set_source_resolution(72);

The TesseractError enum captures all possible failures during the OCR process. Common error variants include:

• InitializeError: Failed to set language or initialize the API.
• SetImageError: Failed to read an image file.
• RecognizeError: Error during the recognition phase.
• GetTextError: Error retrieving UTF-8 text.
• GetHOCRTextError: Error retrieving HOCR text.
• GetTsvTextError: Error retrieving TSV text.
• SetVariableError: Error setting a configuration variable.