toPixelMap

Function

Common

fun ImageBitmap.toPixelMap(
    startX: Int = 0,
    startY: Int = 0,
    width: Int = this.width,
    height: Int = this.height,
    buffer: IntArray = IntArray(width * height),
    bufferOffset: Int = 0,
    stride: Int = width,
): PixelMap

Convenience method to extract pixel information from the given ImageBitmap into a PixelMap that supports for querying pixel information based on

Note this method can block so it is recommended to not invoke this method in performance critical code paths

Parameters


startX	The x-coordinate of the first pixel to read from the `ImageBitmap`
startY	The y-coordinate of the first pixel to read from the `ImageBitmap`
width	The number of pixels to read from each row
height	The number of rows to read
buffer	The array to store the `ImageBitmap`'s colors. By default this allocates an `IntArray` large enough to store all the pixel information. Consumers of this API are advised to use the smallest `IntArray` necessary to extract relevant pixel information
bufferOffset	The first index to write into the buffer array, this defaults to 0
stride	The number of entries in `buffer` to skip between rows (must be >= `width`

Code Examples

ImageBitmapToPixelMapSample

/**
 * Sample showing how to obtain a [PixelMap] to query pixel information from an underlying
 * [ImageBitmap]
 */
fun ImageBitmapToPixelMapSample() {
    val imageBitmap = createImageBitmap()
    // Sample a 3 by 2 subsection of the given ImageBitmap
    // starting at the coordinate (48, 49)
    val pixelmap = imageBitmap.toPixelMap(startX = 48, startY = 49, width = 3, height = 2)
    // create a histogram to count the number of occurrences of a color within the specified
    // subsection of the provided ImageBitmap
    val histogram = HashMap<Color, Int>()
    for (x in 0 until pixelmap.width) {
        for (y in 0 until pixelmap.height) {
            val color = pixelmap[x, y]
            val colorCount = histogram[color] ?: 0
            histogram[color] = (colorCount + 1)
        }
    }
}