Feature: Image Editing

Relevant source files

The following files were used as context for generating this wiki page:

• app/src/main/java/com/musagenius/ocrapp/data/utils/ImageEditor.kt
• app/src/main/java/com/musagenius/ocrapp/MainActivity.kt
• app/src/main/java/com/musagenius/ocrapp/data/ocr/ImagePreprocessor.kt
• app/src/main/java/com/musagenius/ocrapp/presentation/viewmodel/OCRViewModel.kt
• app/src/main/java/com/musagenius/ocrapp/presentation/ui/ocr/OCRResultScreen.kt

The Image Editing feature provides users with the ability to perform basic modifications, such as rotation and cropping, on images selected from the device's gallery. This step is crucial for preparing images for Optical Character Recognition (OCR), ensuring they are correctly oriented and focused on the relevant area, thereby improving the accuracy of text extraction. The feature is integrated into the app's workflow between image selection and OCR processing.

The editing functionality is primarily encapsulated within the ImageEditor utility class, which handles the low-level bitmap manipulations. The application's navigation graph, defined in MainActivity, orchestrates the user flow, directing the user from the gallery selection to the ImageEditorScreen, and subsequently to the OCRResultScreen upon saving the edits.

Architecture and Components

The Image Editing feature is composed of several key components that work together to provide a seamless user experience. The core logic is decoupled from the UI, following clean architecture principles.

The diagram below illustrates the main components and their relationships.

Key Components

Component	File	Description
MainActivity	MainActivity.kt	Contains the Jetpack Navigation graph. It defines the route to the ImageEditorScreen and handles passing the image URI as an argument. It also manages navigation to the OCRResultScreen after editing is complete.
ImageEditorScreen	ImageEditorScreen.kt	The UI component where the user interacts with the image to perform edits. It receives the image URI, and upon saving, returns the URI of the newly edited image. (Note: File not present in context, behavior inferred from MainActivity.kt).
ImageEditor	ImageEditor.kt	A singleton utility class responsible for all image manipulation logic, including rotation, cropping, and saving the modified bitmap to a new file.
ImageCompressor	ImageCompressor.kt	A dependency of ImageEditor, used to load the initial bitmap from a source URI. (Note: File not present, inferred from ImageEditor.kt constructor).
ImagePreprocessor	ImagePreprocessor.kt	Contains related image manipulation logic, such as an alternative rotateBitmap function, scaling, and quality assessment, which complements the overall image handling capabilities of the app.

Sources: app/src/main/java/com/musagenius/ocrapp/MainActivity.kt:65-87, app/src/main/java/com/musagenius/ocrapp/data/utils/ImageEditor.kt:17-23, app/src/main/java/com/musagenius/ocrapp/data/ocr/ImagePreprocessor.kt:18-24

Data Flow

The image editing process follows a specific sequence, starting from the user selecting an image from the gallery and ending with the edited image being sent for OCR.

This sequence diagram shows the interactions between the user, UI, and data-layer components.

Core Logic: ImageEditor

The ImageEditor class is the heart of the editing feature. It is an injectable singleton that provides suspend functions for performing image manipulations on background threads to avoid blocking the UI.

Sources: app/src/main/java/com/musagenius/ocrapp/data/utils/ImageEditor.kt:17-23

Class Diagram

Key Functions

Function	Parameters	Return Type	Description
rotateBitmap	bitmap: Bitmap, degrees: Float	Bitmap	Rotates the input bitmap by the specified degrees using android.graphics.Matrix. It recycles the original bitmap if a new one is created.
cropBitmap	bitmap: Bitmap, x: Int, y: Int, width: Int, height: Int	Bitmap	Crops the bitmap to the specified rectangle. It ensures crop bounds are valid and recycles the original bitmap.
saveBitmapToUri	bitmap: Bitmap, quality: Int = 90	Result<Uri>	Saves the given bitmap to a temporary .jpg file in the app's external files directory with a default JPEG quality of 90. Returns a Result containing the Uri of the saved file.
editImage	sourceUri: Uri, rotationDegrees: Float, cropRect: CropRect?	Result<Uri>	The main orchestration function. It loads a bitmap from the sourceUri, applies rotation and/or cropping, saves the result to a new file, and returns the Uri of the edited image.

Sources: app/src/main/java/com/musagenius/ocrapp/data/utils/ImageEditor.kt:29-132

The editImage function provides a complete pipeline for applying edits:

// Source: app/src/main/java/com/musagenius/ocrapp/data/utils/ImageEditor.kt:102-132
suspend fun editImage(
    sourceUri: Uri,
    rotationDegrees: Float = 0f,
    cropRect: CropRect? = null
): Result<Uri> = withContext(Dispatchers.IO) {
    try {
        // 1. Load bitmap from URI
        var bitmap = imageCompressor.loadBitmapFromUri(sourceUri)
            ?: return@withContext Result.failure(Exception("Failed to load image"))

        // 2. Apply rotation if specified
        if (rotationDegrees != 0f) {
            bitmap = rotateBitmap(bitmap, rotationDegrees)
        }

        // 3. Apply crop if specified
        if (cropRect != null) {
            bitmap = cropBitmap(
                bitmap,
                cropRect.x,
                cropRect.y,
                cropRect.width,
                cropRect.height
            )
        }

        // 4. Save edited bitmap to file
        val result = saveBitmapToUri(bitmap, quality = 90)

        // 5. Clean up bitmap
        if (!bitmap.isRecycled) {
            bitmap.recycle()
        }

        result
    } catch (e: Exception) {
        Result.failure(e)
    }
}

Navigation Integration

The MainActivity is responsible for integrating the ImageEditorScreen into the application's navigation flow. When an image is selected from the gallery on the CameraScreen, it triggers a navigation event to the editor.

Sources: app/src/main/java/com/musagenius/ocrapp/MainActivity.kt:60-63

The navigation graph includes a composable destination for the editor route:

• Route: Screen.ImageEditor.route which is defined as image_editor/{imageUri}.
• Argument: It accepts a mandatory imageUri string argument. The URI is encoded before being passed in the route and decoded upon arrival.
• Callbacks:
  • onImageSaved: This callback is invoked when the user saves their edits. It receives the Uri of the new, edited image. The app then navigates to the OCRResultScreen, passing this new URI. The navigation action also pops the back stack up to the CameraScreen, removing the editor from the history.
  • onCancel: If the user cancels the editing process, this callback is invoked, and the app simply pops the back stack, returning to the previous screen (CameraScreen).

Sources: app/src/main/java/com/musagenius/ocrapp/MainActivity.kt:65-87

Conclusion

The Image Editing feature is a well-defined module that enhances the application's core OCR functionality. By providing essential tools for rotation and cropping, it empowers users to improve the quality of input images, leading to more accurate text extraction. The feature's architecture effectively separates the complex image manipulation logic in the ImageEditor utility from the UI and navigation concerns, which are handled by Jetpack Compose and Navigation components. This separation makes the feature robust, testable, and easy to maintain.