added parameter metadataOnly to InitializeDerivedData: If true, memory allocation will not be done

src/ImageSharp/Formats/Jpeg/GolangPort/Components/Decoder/OrigComponent.cs

@@ -57,7 +57,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
         /// </summary>
         /// <param name="memoryManager">The <see cref="MemoryManager"/> to use for buffer allocations.</param>
         /// <param name="decoder">The <see cref="OrigJpegDecoderCore"/> instance</param>
-        public void InitializeDerivedData(MemoryManager memoryManager, OrigJpegDecoderCore decoder)
+        /// <param name="metadataOnly">Whether to decode metadata only. If this is true, memory allocation for SpectralBlocks will not be necessary</param>
+        public void InitializeDerivedData(MemoryManager memoryManager, OrigJpegDecoderCore decoder, bool metadataOnly)
         {
             // For 4-component images (either CMYK or YCbCrK), we only support two
             // hv vectors: [0x11 0x11 0x11 0x11] and [0x22 0x11 0x11 0x22].
@@ -80,7 +81,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
                 this.SubSamplingDivisors = c0.SamplingFactors.DivideBy(this.SamplingFactors);
             }
 
-            this.SpectralBlocks = memoryManager.Allocate2D<Block8x8>(this.SizeInBlocks.Width, this.SizeInBlocks.Height, true);
+            if (!metadataOnly)
+            {
+                this.SpectralBlocks = memoryManager.Allocate2D<Block8x8>(this.SizeInBlocks.Width, this.SizeInBlocks.Height, true);
+            }
         }
 
         /// <summary>

src/ImageSharp/Formats/Jpeg/GolangPort/OrigJpegDecoderCore.cs

@@ -692,12 +692,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
 
             this.ColorSpace = this.DeduceJpegColorSpace();
 
-            if (!metadataOnly)
+            foreach (OrigComponent component in this.Components)
             {
-                foreach (OrigComponent component in this.Components)
-                {
-                    component.InitializeDerivedData(this.configuration.MemoryManager, this);
-                }
+                component.InitializeDerivedData(this.configuration.MemoryManager, this, metadataOnly);
             }
         }