Jpeg colorspace is undefined after metadata only (Identify call) pass

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I have verified that I am running the latest version of ImageSharp
I have verified if the problem exist in both DEBUG and RELEASE mode
I have searched open and closed issues to ensure it has not already been reported

Description

Jpeg color space is undefined after metadataOnly decoding pass. This is happening because colorspace deduction (and metadata population) logic is locked behind if(!metadataOnly) check in SOF marker parsing (line 916):

ImageSharp/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

Lines 868 to 918 in fe65a38

    
           if (!metadataOnly) 
        
           { 
        
               remaining -= length; 
        
               const int componentBytes = 3; 
        
               if (remaining > this.ComponentCount * componentBytes) 
        
               { 
        
                   JpegThrowHelper.ThrowBadMarker("SOFn", remaining); 
        
               } 
        
               stream.Read(this.temp, 0, remaining); 
        
               // No need to pool this. They max out at 4 
        
               this.Frame.ComponentIds = new byte[this.ComponentCount]; 
        
               this.Frame.ComponentOrder = new byte[this.ComponentCount]; 
        
               this.Frame.Components = new JpegComponent[this.ComponentCount]; 
        
               this.ColorSpace = this.DeduceJpegColorSpace(); 
        
               int maxH = 0; 
        
               int maxV = 0; 
        
               int index = 0; 
        
               for (int i = 0; i < this.ComponentCount; i++) 
        
               { 
        
                   byte hv = this.temp[index + 1]; 
        
                   int h = (hv >> 4) & 15; 
        
                   int v = hv & 15; 
        
                   if (maxH < h) 
        
                   { 
        
                       maxH = h; 
        
                   } 
        
                   if (maxV < v) 
        
                   { 
        
                       maxV = v; 
        
                   } 
        
                   var component = new JpegComponent(this.Configuration.MemoryAllocator, this.Frame, this.temp[index], h, v, this.temp[index + 2], i); 
        
                   this.Frame.Components[i] = component; 
        
                   this.Frame.ComponentIds[i] = component.Id; 
        
                   index += componentBytes; 
        
               } 
        
               this.Frame.MaxHorizontalFactor = maxH; 
        
               this.Frame.MaxVerticalFactor = maxV; 
        
               this.ColorSpace = this.DeduceJpegColorSpace(); 
        
               this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr; 
        
               this.Frame.InitComponents(); 
        
               this.ImageSizeInMCU = new Size(this.Frame.McusPerLine, this.Frame.McusPerColumn);

Steps to Reproduce

var info = Image.Identify("image_path");
Console.WriteLine(info.Metadata.GetFormatMetadata(JpegFormat.Instance).ColorType.HasValue); // prints false

using var image = Image.Load("image_path");
Console.WriteLine(image.Metadata.GetFormatMetadata(JpegFormat.Instance).ColorType.HasValue); // prints true

As this breaks existing jpeg decoder tests it'll be fixed as part of #1597.

Ha! well spotted! We're deducing the colorspace 2 times. Once at line 884 and once at line 916 but hiding both in that block!

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Jpeg colorspace is undefined after metadata only (Identify call) pass #1692

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	if (!metadataOnly)
	{
	remaining -= length;

	const int componentBytes = 3;
	if (remaining > this.ComponentCount * componentBytes)
	{
	JpegThrowHelper.ThrowBadMarker("SOFn", remaining);
	}

	stream.Read(this.temp, 0, remaining);

	// No need to pool this. They max out at 4
	this.Frame.ComponentIds = new byte[this.ComponentCount];
	this.Frame.ComponentOrder = new byte[this.ComponentCount];
	this.Frame.Components = new JpegComponent[this.ComponentCount];
	this.ColorSpace = this.DeduceJpegColorSpace();

	int maxH = 0;
	int maxV = 0;
	int index = 0;
	for (int i = 0; i < this.ComponentCount; i++)
	{
	byte hv = this.temp[index + 1];
	int h = (hv >> 4) & 15;
	int v = hv & 15;

	if (maxH < h)
	{
	maxH = h;
	}

	if (maxV < v)
	{
	maxV = v;
	}

	var component = new JpegComponent(this.Configuration.MemoryAllocator, this.Frame, this.temp[index], h, v, this.temp[index + 2], i);

	this.Frame.Components[i] = component;
	this.Frame.ComponentIds[i] = component.Id;

	index += componentBytes;
	}

	this.Frame.MaxHorizontalFactor = maxH;
	this.Frame.MaxVerticalFactor = maxV;
	this.ColorSpace = this.DeduceJpegColorSpace();
	this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr;
	this.Frame.InitComponents();
	this.ImageSizeInMCU = new Size(this.Frame.McusPerLine, this.Frame.McusPerColumn);

Jpeg colorspace is undefined after metadata only (Identify call) pass #1692

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br3aker commented on Jul 11, 2021

JimBobSquarePants commented on Jul 11, 2021

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