Class JpegTransform

Namespace

Egami.Formats.Jpeg

Assembly

Egami.dll

Rotates, flips, crops and drops the color of JPEG files without decoding them to pixels, so nothing is lost: the quantized DCT coefficients are moved and sign-flipped block by block, as jpegtran does, and coded again. Quantization tables and chroma subsampling stay as they were. Every mode the reader takes works except lossless JPEG, which has no coefficients.

public static class JpegTransform

Inheritance

object

JpegTransform

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Examples

// Turns the photo upright by its EXIF orientation without re-encoding: no quality is lost, and the tag is reset.
JpegTransform.Apply("sideways.jpg", "upright.jpg", new JpegTransformOptions { Operation = JpegTransformOperation.AutoOrient });

// Rotates, crops and drops the color in one pass; a file can be transformed in place.
JpegTransformResult result = JpegTransform.Apply("upright.jpg", "upright.jpg", new JpegTransformOptions
{
    Operation = JpegTransformOperation.Rotate90,
    Crop = new Rect(0, 0, 200, 120),
    Grayscale = true,
});
Console.WriteLine($"{result.Width} × {result.Height}");

Remarks

The whole image's coefficients are held while it runs (about 2 bytes per sample, 3 bytes per pixel for a 4:2:0 photo), counted against MaxTotalBytes. The result is the same for any MaxParallelism.

Methods

Apply(Stream, Stream, JpegTransformOptions, EgamiContext?)

Transforms the JPEG in source and writes the result to destination.

public static JpegTransformResult Apply(Stream source, Stream destination, JpegTransformOptions options, EgamiContext? context = null)

Parameters

source Stream

The JPEG, read from its current position. It is not disposed.

destination Stream

Where the result goes. It is not disposed.

options JpegTransformOptions

What to do.

context EgamiContext

The context whose limits and diagnostics apply, or null for Default.

Returns

JpegTransformResult

The size of the result and the warnings.

Examples

// Turns the photo upright by its EXIF orientation without re-encoding: no quality is lost, and the tag is reset.
JpegTransform.Apply("sideways.jpg", "upright.jpg", new JpegTransformOptions { Operation = JpegTransformOperation.AutoOrient });

// Rotates, crops and drops the color in one pass; a file can be transformed in place.
JpegTransformResult result = JpegTransform.Apply("upright.jpg", "upright.jpg", new JpegTransformOptions
{
    Operation = JpegTransformOperation.Rotate90,
    Crop = new Rect(0, 0, 200, 120),
    Grayscale = true,
});
Console.WriteLine($"{result.Width} × {result.Height}");

Exceptions

ArgumentNullException

An argument is null.

ArgumentOutOfRangeException

Crop is empty or leaves the image.

InvalidOperationException

Strict and a partial MCU would move.

NotSupportedException

Grayscale on an RGB, CMYK or YCCK file.

UnsupportedFormatException

The file is lossless or hierarchical JPEG.

CorruptDataException

The file breaks the format's rules beyond repair.

LimitExceededException

The image is larger than the limits allow, or its coefficients need more memory.

Apply(string, string, JpegTransformOptions, EgamiContext?)

Transforms a JPEG file into another, or into itself: the result goes to a temporary file beside destinationPath that replaces it once complete, so a failure leaves the destination as it was.

public static JpegTransformResult Apply(string sourcePath, string destinationPath, JpegTransformOptions options, EgamiContext? context = null)

Parameters

sourcePath string

The JPEG file.

destinationPath string

The file to write; it may be sourcePath.

options JpegTransformOptions

What to do.

context EgamiContext

The context whose limits and diagnostics apply, or null for Default.

Returns

JpegTransformResult

The size of the result and the warnings.

Examples

// Turns the photo upright by its EXIF orientation without re-encoding: no quality is lost, and the tag is reset.
JpegTransform.Apply("sideways.jpg", "upright.jpg", new JpegTransformOptions { Operation = JpegTransformOperation.AutoOrient });

// Rotates, crops and drops the color in one pass; a file can be transformed in place.
JpegTransformResult result = JpegTransform.Apply("upright.jpg", "upright.jpg", new JpegTransformOptions
{
    Operation = JpegTransformOperation.Rotate90,
    Crop = new Rect(0, 0, 200, 120),
    Grayscale = true,
});
Console.WriteLine($"{result.Width} × {result.Height}");

Exceptions

ArgumentNullException

An argument is null.

ArgumentOutOfRangeException

Crop is empty or leaves the image.

InvalidOperationException

Strict and a partial MCU would move.

NotSupportedException

Grayscale on an RGB, CMYK or YCCK file.

UnsupportedFormatException

The file is lossless or hierarchical JPEG.

CorruptDataException

The file breaks the format's rules beyond repair.

LimitExceededException

The image is larger than the limits allow, or its coefficients need more memory.

IOException

A file cannot be read or written.