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

@br3aker

Description

@br3aker

Prerequisites

  • I have written a descriptive issue title
  • 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):

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

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