Image utilities

Utilities for working with images in Kotlin Multiplatform

Supported on Android, iOS, macOS, JVM targets

FileKit Core provides powerful utilities for working with images across platforms. These utilities enable common image operations like compression, resizing, and saving to the device gallery, with a consistent API across all supported platforms.

Compressing Images

You can compress images to reduce their file size while maintaining acceptable quality:

suspend fun compressAndSaveImage() {
    // Read an image file
    val originalImageFile = PlatformFile("/path/to/original.jpg")
    val imageBytes = originalImageFile.readBytes()
    
    // Compress the image
    val compressedBytes = FileKit.compressImage(
        bytes = imageBytes,
        quality = 80, // 0-100, where 100 is highest quality
        maxWidth = 1024, // Optional maximum width
        maxHeight = 1024, // Optional maximum height
        imageFormat = ImageFormat.JPEG // JPEG or PNG
    )
    
    // Save the compressed image
    val compressedFile = PlatformFile(FileKit.filesDir, "compressed.jpg")
    compressedFile.write(compressedBytes)
}

The compressImage function provides several key features:

• Quality control: Reduces the image quality based on the quality parameter (0-100)
• Resizing: Resizes the image if maxWidth or maxHeight is specified, maintaining the aspect ratio
• Format conversion: Converts the image to the specified format (JPEG or PNG)
• Metadata handling: On Android, automatically handles EXIF orientation metadata

Saving Images to Gallery

FileKit provides a way to save images to the device’s photo gallery:

suspend fun saveImageToDeviceGallery() {
    // Read an image file
    val imageFile = PlatformFile(FileKit.filesDir, "photo.jpg")

    // Save to the device's photo gallery
    FileKit.saveImageToGallery(file = imageFile)
}

The behavior of saveImageToGallery varies slightly by platform:

Platform	Behavior
Android	Saves to the device’s Pictures directory and makes it visible in the gallery app
iOS	Saves to the device’s Camera Roll
macOS/JVM	Saves to the user’s Pictures directory
JS/WASM	Not supported (no-op)

Encoding and Converting Images

FileKit provides utilities for encoding ImageBitmap objects into byte arrays and converting PlatformFile objects into ImageBitmap instances. These methods are useful for image manipulation and storage across platforms.

Encoding an ImageBitmap to ByteArray

The ImageBitmap.encodeToByteArray method allows you to encode an ImageBitmap into a ByteArray using a specified format and quality.

suspend fun encodeImageToByteArray(imageBitmap: ImageBitmap): ByteArray {
    return imageBitmap.encodeToByteArray(
        format = ImageFormat.JPEG, // JPEG or PNG
        quality = 90 // Compression quality (0-100)
    )
}

Converting a PlatformFile to ImageBitmap

The PlatformFile.toImageBitmap method converts a file into an ImageBitmap for use in Compose UI or other image operations.

suspend fun convertFileToImageBitmap(file: PlatformFile): ImageBitmap {
    return file.toImageBitmap()
}

Example: Creating a Thumbnail

This function creates a thumbnail version of an image by resizing it to a maximum dimension while maintaining the aspect ratio.

suspend fun createThumbnail(originalImageFile: PlatformFile, maxSize: Int = 200): PlatformFile {
    // Read the original image
    val imageBytes = originalImageFile.readBytes()
    
    // Create a thumbnail by compressing and resizing
    val thumbnailBytes = FileKit.compressImage(
        bytes = imageBytes,
        quality = 85,
        maxWidth = maxSize,
        maxHeight = maxSize,
        imageFormat = ImageFormat.JPEG
    )
    
    // Save the thumbnail
    val thumbnailFile = PlatformFile(
        FileKit.cacheDir,
        "thumb_${originalImageFile.nameWithoutExtension}.jpg"
    )
    thumbnailFile write thumbnailBytes
    
    return thumbnailFile
}