Этап 2

Minint.Core/Services/IImageEffectService.cs

@@ -0,0 +1,20 @@
+using Minint.Core.Models;
+
+namespace Minint.Core.Services;
+
+public interface IImageEffectService
+{
+    /// <summary>
+    /// Adjusts contrast of the document by modifying palette colors.
+    /// <paramref name="factor"/> > 1 increases contrast, &lt; 1 decreases.
+    /// Index 0 (transparent) is not modified.
+    /// </summary>
+    void AdjustContrast(MinintDocument document, float factor);
+
+    /// <summary>
+    /// Converts the document to grayscale by modifying palette colors.
+    /// Uses ITU-R BT.601 luminance: gray = 0.299R + 0.587G + 0.114B.
+    /// Index 0 (transparent) is not modified.
+    /// </summary>
+    void ToGrayscale(MinintDocument document);
+}