Class ImageHeaderUtils

Reads the pixel size an image file declares in its header, without decoding it, so a file can be refused for its size before anything allocates memory for its pixels.

Inheritance

object

ImageHeaderUtils

Inherited Members

object.ToString()

object.Equals(object)

object.Equals(object, object)

object.ReferenceEquals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

Namespace: Serenity.Shared.Utils

Assembly: Serenity.Shared.dll

Syntax

public static class ImageHeaderUtils

Remarks

PNG keeps its size in the first chunk (IHDR) and JPEG in its first start-of-frame segment. Only the declared size is read; nothing here says the rest of the file is a valid image.

The JPEG walk is as strict as a decoder, so a file cannot show this reader one frame header and a decoder another. After the start-of-image marker it accepts only fill bytes, the standalone markers TEM and RST0-RST7, and the length-carrying segments DHT, DAC, DQT, DRI, APP0-APP15 and COM, skipped by their declared length (which must fit in the file); it stops at the first start-of-frame marker and reads the size there. Any other marker met first — a second start-of-image, an end-of-image, a start-of-scan, a reserved or extension marker, a stuffed FF00 — makes the file unreadable, as does a frame header whose length does not match its component count.

Methods

HasJpegSignature(byte[])

Whether the bytes begin with a JPEG start-of-image marker followed by another marker.

Declaration

public static bool HasJpegSignature(byte[] imageBytes)

Parameters

Type	Name	Description
byte[]	imageBytes	The file's bytes. May be null.

Returns

Type	Description
bool

HasPngSignature(byte[])

Whether the bytes begin with the PNG file signature.

Declaration

public static bool HasPngSignature(byte[] imageBytes)

Parameters

Type	Name	Description
byte[]	imageBytes	The file's bytes. May be null.

Returns

Type	Description
bool

TryReadDimensions(byte[], out int, out int)

Reads the size a PNG or JPEG declares.

Declaration

public static bool TryReadDimensions(byte[] imageBytes, out int width, out int height)

Parameters

Type	Name	Description
byte[]	imageBytes	The file's bytes. May be null.
int	width	The declared width in pixels; zero when the size could not be read.
int	height	The declared height in pixels; zero when the size could not be read.

Returns

Type	Description
bool	True when the file is a PNG or JPEG whose header declares a size.