make alppha process pecentage consistent with blenders

src/ImageSharp/Processing/Effects/Alpha.cs

@@ -21,9 +21,9 @@ namespace ImageSharp
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="source">The image this method extends.</param>
-        /// <param name="percent">The new opacity of the image. Must be between 0 and 100.</param>
+        /// <param name="percent">The new opacity of the image. Must be between 0 and 1.</param>
         /// <returns>The <see cref="Image{TPixel}"/>.</returns>
-        public static Image<TPixel> Alpha<TPixel>(this Image<TPixel> source, int percent)
+        public static Image<TPixel> Alpha<TPixel>(this Image<TPixel> source, float percent)
             where TPixel : struct, IPixel<TPixel>
         {
             return Alpha(source, percent, source.Bounds);
@@ -34,12 +34,12 @@ namespace ImageSharp
         /// </summary>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <param name="source">The image this method extends.</param>
-        /// <param name="percent">The new opacity of the image. Must be between 0 and 100.</param>
+        /// <param name="percent">The new opacity of the image. Must be between 0 and 1.</param>
         /// <param name="rectangle">
         /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
         /// </param>
         /// <returns>The <see cref="Image"/>.</returns>
-        public static Image<TPixel> Alpha<TPixel>(this Image<TPixel> source, int percent, Rectangle rectangle)
+        public static Image<TPixel> Alpha<TPixel>(this Image<TPixel> source, float percent, Rectangle rectangle)
             where TPixel : struct, IPixel<TPixel>
         {
             source.ApplyProcessor(new AlphaProcessor<TPixel>(percent), rectangle);

src/ImageSharp/Processing/Processors/Effects/AlphaProcessor.cs

@@ -21,26 +21,24 @@ namespace ImageSharp.Processing.Processors
         /// <summary>
         /// Initializes a new instance of the <see cref="AlphaProcessor{TPixel}"/> class.
         /// </summary>
-        /// <param name="percent">The percentage to adjust the opacity of the image. Must be between 0 and 100.</param>
+        /// <param name="percent">The percentage to adjust the opacity of the image. Must be between 0 and 1.</param>
         /// <exception cref="System.ArgumentException">
-        /// <paramref name="percent"/> is less than 0 or is greater than 100.
+        /// <paramref name="percent"/> is less than 0 or is greater than 1.
         /// </exception>
-        public AlphaProcessor(int percent)
+        public AlphaProcessor(float percent)
         {
-            Guard.MustBeBetweenOrEqualTo(percent, 0, 100, nameof(percent));
+            Guard.MustBeBetweenOrEqualTo(percent, 0, 1, nameof(percent));
             this.Value = percent;
         }
 
         /// <summary>
         /// Gets the alpha value.
         /// </summary>
-        public int Value { get; }
+        public float Value { get; }
 
         /// <inheritdoc/>
         protected override void OnApply(ImageBase<TPixel> source, Rectangle sourceRectangle)
         {
-            float alpha = this.Value / 100F;
-
             int startY = sourceRectangle.Y;
             int endY = sourceRectangle.Bottom;
             int startX = sourceRectangle.X;
@@ -63,7 +61,7 @@ namespace ImageSharp.Processing.Processors
                 startY = 0;
             }
 
-            Vector4 alphaVector = new Vector4(1, 1, 1, alpha);
+            Vector4 alphaVector = new Vector4(1, 1, 1, this.Value);
 
             using (PixelAccessor<TPixel> sourcePixels = source.Lock())
             {