Here's the result running on iOS, Android, and Universal Windows Platform:
#Convert image to black and white code#
The DrawBitmap method used in this code is from the BitmapExtension.cs file included with the SkiaSharpFormsDemos sample. SKColorFilter.CreateColorMatrix(new floatĬanvas.DrawBitmap(bitmap, info.Rect, BitmapStretch.Uniform, paint: paint) Void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args) SKCanvasView canvasView = new SKCanvasView() ĬanvasView.PaintSurface += OnCanvasViewPaintSurface SKBitmap bitmap = BitmapExtensions.LoadBitmapResource(
This is demonstrated in the Gray-Scale Matrix page in the SkiaSharpFormsDemos sample: public class GrayScaleMatrixPage : ContentPage When creating the array in C#, it is easy to format the numbers so they resemble the 4×5 matrix. Where matrix is an array of the 20 float values. The static SKColorFilter.CreateColorMatrix method has the following syntax: public static SKColorFilter CreateColorMatrix (float matrix) Instead you must represent the matrix as an array of 20 float values in row order: first row, then second row, and so forth. There is no SkiaSharp data type that corresponds to this matrix.
To convert a color bitmap to a gray-scale bitmap, the R', G', and B' results must all equal that same value. For video displays using the sRGB ("standard red green blue") color space, this formula is: This involves a formula for a weighted average of the red, green, and blue values. One of the most common uses of the color matrix is to convert a color bitmap to a gray-scale bitmap. But if M44 is zero, then A' will be zero, and nothing will be visible. It is generally the case that M41, M42, and M43 are all zero, because you probably don't want opacity to be based on the red, green, and blue values. The M44 cell is very important because it preserves opacity. The results are clamped between the values of 0 and 255. These values generally range from 0 to 255. However, the last column (M15 through M45) contains values that are added in the formulas. Most of the matrix consists of multiplicative factors that are generally in the range of 0 to 2. Here are the separate formulas for R', G', B', and A': The 4×5 matrix is multiplied by the 5×1 matrix, and the product is a 4×1 matrix with the transformed color: This is analogous to the use of a 3×3 matrix to transform two-dimensional coordinate points as described in the section The Reason for the 3-by-3 Matrix in the article on using matrices for transforming coordinate points. The extra cell is required for a translation factor. They are not normalized to floating point values in the range 0 to 1. These R, G, B, and A values are the original bytes ranging from 0 to 255. In preparation for the matrix multiplication, the source color is converted to a 5×1 matrix: It transforms a RGB source color (R, G, B, A) to the destination color (R', G', B', A'). The color-transform matrix has a dimension of four rows and five columns: Some familiarity with matrix concepts is necessary to understand these color transforms. The SKColorFilter also supports matrix transforms, but the matrix transforms RGB colors. Like most 2D graphics systems, SkiaSharp uses matrices mostly for transforming coordinate points as iscussed in the article Matrix Transforms in SkiaSharp. The color transform involves using a matrix to modify colors.
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