Class jpeg_decompress_struct

JPEG decompression routine.

Inheritance
System.Object
jpeg_common_struct
jpeg_decompress_struct
Inherited Members
System.Object.ToString()
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
Namespace: BitMiracle.LibJpeg.Classic
Assembly: BitMiracle.LibJpeg.NET.dll
Syntax
public class jpeg_decompress_struct : jpeg_common_struct

Constructors

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jpeg_decompress_struct()

Initializes a new instance of the jpeg_decompress_struct class.

Declaration
public jpeg_decompress_struct()
See Also
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jpeg_decompress_struct(jpeg_error_mgr)

Initializes a new instance of the jpeg_decompress_struct class.

Declaration
public jpeg_decompress_struct(jpeg_error_mgr errorManager)
Parameters
Type Name Description
jpeg_error_mgr errorManager

The error manager.
See Also

Properties

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Actual_number_of_colors

The number of colors in the color map.

Declaration
public int Actual_number_of_colors { get; set; }
Property Value
Type Description
System.Int32

The number of colors in the color map.
See Also
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Buffered_image

Gets or sets a value indicating whether to use buffered-image mode.

Declaration
public bool Buffered_image { get; set; }
Property Value
Type Description
System.Boolean

true if buffered-image mode is turned on; otherwise, false.
See Also
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Coef_bits

Gets the current progression status..

Declaration
public int[][] Coef_bits { get; }
Property Value
Type Description
System.Int32[][]

Coef_bits[c][i] indicates the precision with which component c's DCT coefficient i (in zigzag order) is known. It is -1 when no data has yet been received, otherwise it is the point transform (shift) value for the most recent scan of the coefficient (thus, 0 at completion of the progression). This is null when reading a non-progressive file.
See Also
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Colormap

The color map, represented as a 2-D pixel array of Out_color_components rows and Actual_number_of_colors columns.

Declaration
public byte[][] Colormap { get; set; }
Property Value
Type Description
System.Byte[][]

Colormap is set to null by jpeg_read_header(Boolean). The application can supply a color map by setting Colormap non-null and setting Actual_number_of_colors to the map size.
Remarks

Ignored if not quantizing.
Implementation restriction: at present, an externally supplied Colormap is only accepted for 3-component output color spaces.

See Also
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Comp_info

Comp_info[i] describes component that appears i'th in SOF

Declaration
public jpeg_component_info[] Comp_info { get; }
Property Value
Type Description
jpeg_component_info[]

The components in SOF.
See Also
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Data_precision

Gets the data precision.

Declaration
public int Data_precision { get; }
Property Value
Type Description
System.Int32

The data precision.
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Dct_method

Gets or sets the algorithm used for the DCT step.

Declaration
public J_DCT_METHOD Dct_method { get; set; }
Property Value
Type Description
J_DCT_METHOD

The algorithm used for the DCT step.
See Also
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Density_unit

Gets the resolution information from JFIF marker.

Declaration
public DensityUnit Density_unit { get; }
Property Value
Type Description
DensityUnit

The information from JFIF marker.
See Also
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Desired_number_of_colors

Maximum number of colors to use in generating a library-supplied color map.

Declaration
public int Desired_number_of_colors { get; set; }
Property Value
Type Description
System.Int32

Default value: 256.
Remarks

Ignored if Quantize_colors is false.
The actual number of colors is returned in a Actual_number_of_colors.

See Also
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Dither_mode

Selects color dithering method.

Declaration
public J_DITHER_MODE Dither_mode { get; set; }
Property Value
Type Description
J_DITHER_MODE

Default value: JDITHER_FS.
Remarks

Ignored if Quantize_colors is false.
At present, ordered dither is implemented only in the single-pass, standard-colormap case. If you ask for ordered dither when Two_pass_quantize is true or when you supply an external color map, you'll get F-S dithering.

See Also
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Do_block_smoothing

Apply interblock smoothing in early stages of decoding progressive JPEG files.

Declaration
public bool Do_block_smoothing { get; set; }
Property Value
Type Description
System.Boolean

If true, interblock smoothing is applied in early stages of decoding progressive JPEG files; if false, not. Early progression stages look "fuzzy" with smoothing, "blocky" without.
Remarks

Default value: true
In any case, block smoothing ceases to be applied after the first few AC coefficients are known to full accuracy, so it is relevant only when using buffered-image mode for progressive images.

See Also
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Do_fancy_upsampling

Enable or disable upsampling of chroma components.

Declaration
public bool Do_fancy_upsampling { get; set; }
Property Value
Type Description
System.Boolean

If true, do careful upsampling of chroma components. If false, a faster but sloppier method is used. The visual impact of the sloppier method is often very small.
Remarks

Default value: true

See Also
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Enable_1pass_quant

Enable future use of 1-pass quantizer.

Declaration
public bool Enable_1pass_quant { get; set; }
Property Value
Type Description
System.Boolean

Default value: false
Remarks

Significant only in buffered-image mode.

See Also
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Enable_2pass_quant

Enable future use of 2-pass quantizer.

Declaration
public bool Enable_2pass_quant { get; set; }
Property Value
Type Description
System.Boolean

Default value: false
Remarks

Significant only in buffered-image mode.

See Also
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Enable_external_quant

Enable future use of external colormap.

Declaration
public bool Enable_external_quant { get; set; }
Property Value
Type Description
System.Boolean

Default value: false
Remarks

Significant only in buffered-image mode.

See Also
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Image_height

Gets the height of image, set by jpeg_read_header(Boolean)

Declaration
public int Image_height { get; }
Property Value
Type Description
System.Int32

The height of image.
See Also
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Image_width

Gets the width of image, set by jpeg_read_header(Boolean)

Declaration
public int Image_width { get; }
Property Value
Type Description
System.Int32

The width of image.
See Also
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Input_iMCU_row

Gets the number of iMCU rows completed.

Declaration
public int Input_iMCU_row { get; }
Property Value
Type Description
System.Int32

The number of iMCU rows completed.
Remarks

Indicates the progress of the decompressor input side.

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Input_scan_number

Gets the number of SOS markers seen so far.

Declaration
public int Input_scan_number { get; }
Property Value
Type Description
System.Int32

The number of SOS markers seen so far.
Remarks

Indicates the progress of the decompressor input side.

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IsDecompressor

Retrieves true because this is a decompressor.

Declaration
public override bool IsDecompressor { get; }
Property Value
Type Description
System.Boolean

true
Overrides
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Jpeg_color_space

Gets or sets the colorspace of JPEG image.

Declaration
public J_COLOR_SPACE Jpeg_color_space { get; set; }
Property Value
Type Description
J_COLOR_SPACE

The colorspace of JPEG image.
See Also
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Marker_list

Gets the list of loaded special markers.

Declaration
public ReadOnlyCollection<jpeg_marker_struct> Marker_list { get; }
Property Value
Type Description
System.Collections.ObjectModel.ReadOnlyCollection<jpeg_marker_struct>

The list of loaded special markers.
Remarks

All the special markers in the file appear in this list, in order of their occurrence in the file (but omitting any markers of types you didn't ask for)

See Also
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Max_v_samp_factor

Gets the largest vertical sample factor.

Declaration
public int Max_v_samp_factor { get; }
Property Value
Type Description
System.Int32

The largest vertical sample factor.
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Num_components

Gets the number of color components in JPEG image.

Declaration
public int Num_components { get; }
Property Value
Type Description
System.Int32

The number of color components.
See Also
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Out_color_components

Gets the number of color components in Out_color_space.

Declaration
public int Out_color_components { get; }
Property Value
Type Description
System.Int32

The number of color components.
Remarks

Computed by jpeg_start_decompress(). You can also use jpeg_calc_output_dimensions() to determine this value in advance of calling jpeg_start_decompress().

See Also
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Out_color_space

Gets or sets the output color space.

Declaration
public J_COLOR_SPACE Out_color_space { get; set; }
Property Value
Type Description
J_COLOR_SPACE

The output color space.
See Also
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Output_components

Gets the number of color components returned.

Declaration
public int Output_components { get; }
Property Value
Type Description
System.Int32

When Quantize_colors, Output_components is 1, indicating a single color map index per pixel. Otherwise it equals to Out_color_components.
Remarks

Computed by jpeg_start_decompress(). You can also use jpeg_calc_output_dimensions() to determine this value in advance of calling jpeg_start_decompress().

See Also
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Output_height

Gets the actual height of output image.

Declaration
public int Output_height { get; }
Property Value
Type Description
System.Int32

The height of output image.
Remarks

Computed by jpeg_start_decompress(). You can also use jpeg_calc_output_dimensions() to determine this value in advance of calling jpeg_start_decompress().

See Also
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Output_iMCU_row

Gets the number of iMCU rows read.

Declaration
public int Output_iMCU_row { get; }
Property Value
Type Description
System.Int32

The number of iMCU rows read.
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Output_scan_number

Gets the nominal scan number being displayed.

Declaration
public int Output_scan_number { get; }
Property Value
Type Description
System.Int32

The nominal scan number being displayed.
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Output_scanline

Gets the number of scanlines returned so far.

Declaration
public int Output_scanline { get; }
Property Value
Type Description
System.Int32

The output_scanline.
Remarks

Usually you can just use this variable as the loop counter, so that the loop test looks like while (cinfo.Output_scanline < cinfo.Output_height)

See Also
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Output_width

Gets the actual width of output image.

Declaration
public int Output_width { get; }
Property Value
Type Description
System.Int32

The width of output image.
Remarks

Computed by jpeg_start_decompress(). You can also use jpeg_calc_output_dimensions() to determine this value in advance of calling jpeg_start_decompress().

See Also
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Quantize_colors

Colors quantization.

Declaration
public bool Quantize_colors { get; set; }
Property Value
Type Description
System.Boolean

If set true, colormapped output will be delivered.
Default value: false, meaning that full-color output will be delivered.
See Also
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Raw_data_out

Enable or disable raw data output.

Declaration
public bool Raw_data_out { get; set; }
Property Value
Type Description
System.Boolean

true if raw data output is enabled; otherwise, false.
Remarks

Default value: false
Set this to true before jpeg_start_decompress() if you need to obtain raw data output.

See Also
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Rec_outbuf_height

Gets the recommended height of scanline buffer.

Declaration
public int Rec_outbuf_height { get; }
Property Value
Type Description
System.Int32

In high-quality modes, Rec_outbuf_height is always 1, but some faster, lower-quality modes set it to larger values (typically 2 to 4).
Remarks

Computed by jpeg_start_decompress(). You can also use jpeg_calc_output_dimensions() to determine this value in advance of calling jpeg_start_decompress().

Rec_outbuf_height is the recommended minimum height (in scanlines) of the buffer passed to jpeg_read_scanlines(Byte[][], Int32). If the buffer is smaller, the library will still work, but time will be wasted due to unnecessary data copying. If you are going to ask for a high-speed processing mode, you may as well go to the trouble of honoring Rec_outbuf_height so as to avoid data copying. (An output buffer larger than Rec_outbuf_height lines is OK, but won't provide any material speed improvement over that height.)

See Also
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Scale_denom

Gets or sets the denominator of the fraction of image scaling.

Declaration
public int Scale_denom { get; set; }
Property Value
Type Description
System.Int32

Scale the image by the fraction Scale_num/Scale_denom. Default is 1/1, or no scaling. Currently, the only supported scaling ratios are 1/1, 1/2, 1/4, and 1/8. (The library design allows for arbitrary scaling ratios but this is not likely to be implemented any time soon.)
Remarks

Smaller scaling ratios permit significantly faster decoding since fewer pixels need to be processed and a simpler J_DCT_METHOD can be used.

See Also
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Scale_num

Gets or sets the numerator of the fraction of image scaling.

Declaration
public int Scale_num { get; set; }
Property Value
Type Description
System.Int32

Scale the image by the fraction Scale_num/Scale_denom. Default is 1/1, or no scaling. Currently, the only supported scaling ratios are 1/1, 1/2, 1/4, and 1/8. (The library design allows for arbitrary scaling ratios but this is not likely to be implemented any time soon.)
Remarks

Smaller scaling ratios permit significantly faster decoding since fewer pixels need to be processed and a simpler J_DCT_METHOD can be used.

See Also
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Src

Gets or sets the source for decompression.

Declaration
public jpeg_source_mgr Src { get; set; }
Property Value
Type Description
jpeg_source_mgr

The source for decompression.
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Two_pass_quantize

Gets or sets a value indicating whether to use two-pass color quantization.

Declaration
public bool Two_pass_quantize { get; set; }
Property Value
Type Description
System.Boolean

If true, an extra pass over the image is made to select a custom color map for the image. This usually looks a lot better than the one-size-fits-all colormap that is used otherwise. Ignored when the application supplies its own color map.

Default value: true
Remarks

Ignored if Quantize_colors is false.

See Also
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Unread_marker

Gets the last read and unprocessed JPEG marker.

Declaration
public int Unread_marker { get; }
Property Value
Type Description
System.Int32

It is either zero or the code of a JPEG marker that has been read from the data source, but has not yet been processed.
See Also
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X_density

Gets the horizontal component of pixel ratio.

Declaration
public short X_density { get; }
Property Value
Type Description
System.Int16

The horizontal component of pixel ratio.
See Also
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Y_density

Gets the vertical component of pixel ratio.

Declaration
public short Y_density { get; }
Property Value
Type Description
System.Int16

The vertical component of pixel ratio.
See Also

Methods

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jpeg_abort_decompress()

Aborts processing of a JPEG decompression operation.

Declaration
public void jpeg_abort_decompress()
See Also
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jpeg_calc_output_dimensions()

Pre-calculate output image dimensions and related values for current decompression parameters.

Declaration
public void jpeg_calc_output_dimensions()
Remarks

This is allowed for possible use by application. Hence it mustn't do anything that can't be done twice. Also note that it may be called before the master module is initialized!

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jpeg_consume_input()

Consume data in advance of what the decompressor requires.

Declaration
public ReadResult jpeg_consume_input()
Returns
Type Description
ReadResult

The result of data consumption.
Remarks

This routine can be called at any time after initializing the JPEG object. It reads some additional data and returns when one of the indicated significant events occurs. If called after the EOI marker is reached, it will immediately return JPEG_REACHED_EOI without attempting to read more data.

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jpeg_copy_critical_parameters(jpeg_compress_struct)

Initializes the compression object with default parameters, then copy from the source object all parameters needed for lossless transcoding.

Declaration
public void jpeg_copy_critical_parameters(jpeg_compress_struct dstinfo)
Parameters
Type Name Description
jpeg_compress_struct dstinfo

Target JPEG compression object.
Remarks

Parameters that can be varied without loss (such as scan script and Huffman optimization) are left in their default states.

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jpeg_finish_decompress()

Finish JPEG decompression.

Declaration
public bool jpeg_finish_decompress()
Returns
Type Description
System.Boolean

Returns false if suspended. The return value need be inspected only if a suspending data source is used.
Remarks

This will normally just verify the file trailer and release temp storage.

See Also
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jpeg_finish_output()

Finish up after an output pass in buffered-image mode.

Declaration
public bool jpeg_finish_output()
Returns
Type Description
System.Boolean

Returns false if suspended. The return value need be inspected only if a suspending data source is used.
See Also
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jpeg_has_multiple_scans()

Is there more than one scan?

Declaration
public bool jpeg_has_multiple_scans()
Returns
Type Description
System.Boolean

true if image has more than one scan; otherwise, false
Remarks

If you are concerned about maximum performance on baseline JPEG files, you should use buffered-image mode only when the incoming file actually has multiple scans. This can be tested by calling this method.

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jpeg_input_complete()

Indicates if we have finished reading the input file.

Declaration
public bool jpeg_input_complete()
Returns
Type Description
System.Boolean

true if we have finished reading the input file.
See Also
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jpeg_read_coefficients()

Read or write the raw DCT coefficient arrays from a JPEG file (useful for lossless transcoding).

Declaration
public jvirt_array<JBLOCK>[] jpeg_read_coefficients()
Returns
Type Description
jvirt_array<JBLOCK>[]

Returns null if suspended. This case need be checked only if a suspending data source is used.
Remarks

jpeg_read_header(Boolean) must be completed before calling this.

The entire image is read into a set of virtual coefficient-block arrays, one per component. The return value is an array of virtual-array descriptors.

An alternative usage is to simply obtain access to the coefficient arrays during a buffered-image mode decompression operation. This is allowed after any jpeg_finish_output() call. The arrays can be accessed until jpeg_finish_decompress() is called. Note that any call to the library may reposition the arrays, so don't rely on Access(Int32, Int32) results to stay valid across library calls.

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jpeg_read_header(Boolean)

Decompression startup: this will read the source datastream header markers, up to the beginning of the compressed data proper.

Declaration
public ReadResult jpeg_read_header(bool require_image)
Parameters
Type Name Description
System.Boolean require_image

Read a description of Return Value.
Returns
Type Description
ReadResult

If you pass require_image=true (normal case), you need not check for a JPEG_HEADER_TABLES_ONLY return code; an abbreviated file will cause an error exit. JPEG_SUSPENDED is only possible if you use a data source module that can give a suspension return.

This method will read as far as the first SOS marker (ie, actual start of compressed data), and will save all tables and parameters in the JPEG object. It will also initialize the decompression parameters to default values, and finally return JPEG_HEADER_OK. On return, the application may adjust the decompression parameters and then call jpeg_start_decompress(). (Or, if the application only wanted to determine the image parameters, the data need not be decompressed. In that case, call jpeg_abort() to release any temporary space.)

If an abbreviated (tables only) datastream is presented, the routine will return JPEG_HEADER_TABLES_ONLY upon reaching EOI. The application may then re-use the JPEG object to read the abbreviated image datastream(s). It is unnecessary (but OK) to call jpeg_abort() in this case. The JPEG_SUSPENDED return code only occurs if the data source module requests suspension of the decompressor. In this case the application should load more source data and then re-call jpeg_read_header to resume processing.

If a non-suspending data source is used and require_image is true, then the return code need not be inspected since only JPEG_HEADER_OK is possible.
Remarks

Need only initialize JPEG object and supply a data source before calling.
On return, the image dimensions and other info have been stored in the JPEG object. The application may wish to consult this information before selecting decompression parameters.
This routine is now just a front end to jpeg_consume_input(), with some extra error checking.

See Also
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jpeg_read_raw_data(Byte[][][], Int32)

Alternate entry point to read raw data.

Declaration
public int jpeg_read_raw_data(byte[][][] data, int max_lines)
Parameters
Type Name Description
System.Byte[][][] data

The raw data.
System.Int32 max_lines

The number of scanlines for reading.
Returns
Type Description
System.Int32

The number of lines actually read.
Remarks

Replaces jpeg_read_scanlines(Byte[][], Int32) when reading raw downsampled data. Processes exactly one iMCU row per call, unless suspended.

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jpeg_read_scanlines(Byte[][], Int32)

Read some scanlines of data from the JPEG decompressor.

Declaration
public int jpeg_read_scanlines(byte[][] scanlines, int max_lines)
Parameters
Type Name Description
System.Byte[][] scanlines

Buffer for filling.
System.Int32 max_lines

Required number of lines.
Returns
Type Description
System.Int32

The return value will be the number of lines actually read. This may be less than the number requested in several cases, including bottom of image, data source suspension, and operating modes that emit multiple scanlines at a time.
Remarks

We warn about excess calls to jpeg_read_scanlines since this likely signals an application programmer error. However, an oversize buffer (max_lines > scanlines remaining) is not an error.

See Also
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jpeg_save_markers(Int32, Int32)

Control saving of COM and APPn markers into Marker_list.

Declaration
public void jpeg_save_markers(int marker_code, int length_limit)
Parameters
Type Name Description
System.Int32 marker_code

The marker type to save (see JPEG_MARKER enumeration).
To arrange to save all the special marker types, you need to call this routine 17 times, for COM and APP0-APP15 markers.
System.Int32 length_limit

If the incoming marker is longer than length_limit data bytes, only length_limit bytes will be saved; this parameter allows you to avoid chewing up memory when you only need to see the first few bytes of a potentially large marker. If you want to save all the data, set length_limit to 0xFFFF; that is enough since marker lengths are only 16 bits. As a special case, setting length_limit to 0 prevents that marker type from being saved at all. (That is the default behavior, in fact.)
See Also
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jpeg_set_marker_processor(Int32, jpeg_decompress_struct.jpeg_marker_parser_method)

Sets processor for special marker.

Declaration
public void jpeg_set_marker_processor(int marker_code, jpeg_decompress_struct.jpeg_marker_parser_method routine)
Parameters
Type Name Description
System.Int32 marker_code

The marker code.
jpeg_decompress_struct.jpeg_marker_parser_method routine

The processor.
Remarks

Allows you to supply your own routine to process COM and/or APPn markers on-the-fly as they are read.

See Also
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jpeg_start_decompress()

Decompression initialization.

Declaration
public bool jpeg_start_decompress()
Returns
Type Description
System.Boolean

Returns false if suspended. The return value need be inspected only if a suspending data source is used.
Remarks

jpeg_read_header(Boolean) must be completed before calling this.

If a multipass operating mode was selected, this will do all but the last pass, and thus may take a great deal of time.
See Also
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jpeg_start_output(Int32)

Initialize for an output pass in buffered-image mode.

Declaration
public bool jpeg_start_output(int scan_number)
Parameters
Type Name Description
System.Int32 scan_number

Indicates which scan of the input file is to be displayed; the scans are numbered starting at 1 for this purpose.
Returns
Type Description
System.Boolean

true if done; false if suspended
See Also
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jpeg_stdio_src(Stream)

Sets input stream.

Declaration
public void jpeg_stdio_src(Stream infile)
Parameters
Type Name Description
System.IO.Stream infile

The input stream.
Remarks

The caller must have already opened the stream, and is responsible for closing it after finishing decompression.

See Also

See Also