public override void Init(Stream stream)
{
using (var bh = new ByteHelper(stream))
{
bh.Seek(0, SeekOrigin.Begin);
var imageHeader = bh.ReadBytes(6);
// Should be GIF87a or GIF89a.
IsValid = imageHeader[0] == 'G' && imageHeader[1] == 'I' && imageHeader[2] == 'F' &&
imageHeader[3] == '8' && (imageHeader[4] == '7' || imageHeader[4] == '9') &&
imageHeader[5] == 'a';
if (!IsValid)
{
return;
}
Width = bh.ReadUshort();
Height = bh.ReadUshort();
// GIF files don't specify a resolution.
DpiH = 72;
DpiV = 72;
}
}
public override void Init(Stream stream)
{
using (var bh = new ByteHelper(stream))
{
bh.Seek(0, SeekOrigin.Begin);
bh.IsLsbf = false;
// Start of Image (SOI) marker.
var marker = bh.ReadBytes(2);
if (marker[0] != 0xFF && marker[1] != 0xD8)
{
return;
}
DpiH = DpiV = 96;
int length;
while (stream.Position < stream.Length)
{
marker = bh.ReadBytes(2);
if (marker[0] != 0xFF)
{
throw new Exception("Invalid JPEG file.");
}
switch (marker[1])
{
case 0xE0:
// APP0 (JFIF) marker.
length = bh.ReadUshort();
bh.Seek(7);
var densityUnits = bh.ReadByte();
var xdensity = bh.ReadUshort();
var ydensity = bh.ReadUshort();
if (densityUnits == 1)
{
DpiH = xdensity;
DpiV = ydensity;
}
else if (densityUnits == 2)
{
// Pixels per centimeter
DpiH = PixelsPerMeterToPixelsPerInch(xdensity * 100);
DpiV = PixelsPerMeterToPixelsPerInch(ydensity * 100);
}
bh.Seek(length - 14);
break;
//case 0xE1:
// APP1-marker. This could be an Exif marker.
// TODO: read x/y-resolution from Exif APP1
case 0xFF:
// Filler byte.
bh.Seek(-1, SeekOrigin.Current);
break;
case 0xD0:
case 0xD1:
case 0xD2:
case 0xD3:
case 0xD4:
case 0xD5:
case 0xD6:
case 0xD7:
case 0xD8:
case 0xD9:
// RSTn are used for resync, may be ignored.
break;
case 0xDA:
// SOS (Start of Scan) marker, followed by image data.
IsValid = true;
return;
case 0xC0:
case 0xC1:
case 0xC2:
case 0xC3:
case 0xC5:
case 0xC6:
case 0xC7:
case 0xC8:
case 0xC9:
case 0xCA:
case 0xCB:
case 0xCD:
case 0xCE:
case 0xCF:
// SOFn (Start Of Frame) markers.
length = bh.ReadUshort();
bh.Seek(1);
Height = bh.ReadUshort();
Width = bh.ReadUshort();
bh.Seek(length - 7);
break;
default:
// Irrelevant variable-length packets.
length = bh.ReadUshort();
bh.Seek(length - 2);
break;
}
}
}
}
public override void Init(Stream stream)
{
ushort resolutionUnit = 0;
using (var bh = new ByteHelper(stream))
{
bh.Seek(0, SeekOrigin.Begin);
var byteOrder = bh.ReadAscii(2);
if (byteOrder != "II" && byteOrder != "MM")
{
return;
}
bh.IsLsbf = byteOrder == "II";
bh.Seek(2);
var ifdOffset = bh.ReadUint();
bh.Seek(ifdOffset, SeekOrigin.Begin);
var entryCount = bh.ReadUshort();
for (ushort i = 0; i < entryCount; ++i)
{
var entryTag = bh.ReadUshort();
var fieldType = bh.ReadUshort();
var numberOfComponents = bh.ReadUint();
switch (entryTag)
{
case (int)Tags.ImageWidth:
switch (fieldType)
{
case (ushort)FieldTypes.Short:
Width = bh.ReadUshort();
bh.Seek(2);
break;
case (ushort)FieldTypes.Long:
Width = (int)bh.ReadUint();
break;
}
break;
case (int)Tags.ImageHeight:
switch (fieldType)
{
case (ushort)FieldTypes.Short:
Height = bh.ReadUshort();
bh.Seek(2);
break;
case (ushort)FieldTypes.Long:
Height = (int)bh.ReadUint();
break;
}
break;
case (int)Tags.XResolution:
{
// Field type is always rational.
var tagDataOffset = bh.ReadUint();
var currentOffset = stream.Position;
stream.Seek(tagDataOffset, SeekOrigin.Begin);
var numerator = bh.ReadUint();
var denominator = bh.ReadUint();
DpiH = (int)Math.Round((double)numerator / denominator);
stream.Seek(currentOffset, SeekOrigin.Begin);
break;
}
case (int)Tags.YResolution:
{
// Field type is always rational.
var tagDataOffset = bh.ReadUint();
var currentOffset = stream.Position;
stream.Seek(tagDataOffset, SeekOrigin.Begin);
var numerator = bh.ReadUint();
var denominator = bh.ReadUint();
DpiV = (int)Math.Round((double)numerator / denominator);
stream.Seek(currentOffset, SeekOrigin.Begin);
break;
}
case (int)Tags.ResolutionUnit:
resolutionUnit = bh.ReadUshort();
bh.Seek(2);
break;
default:
bh.Seek(4);
break;
}
}
}
// https://www.awaresystems.be/imaging/tiff/tifftags/resolutionunit.html
if (resolutionUnit == 0 || resolutionUnit == 1)
{
DpiH = DpiV = 72;
}
else if (resolutionUnit == 3)
{
DpiH = PixelsPerMeterToPixelsPerInch(DpiH * 100);
DpiV = PixelsPerMeterToPixelsPerInch(DpiV * 100);
}
IsValid = true;
}