Class: Axon::JPEG::Reader

Inherits:
Object
  • Object
show all
Defined in:
ext/axon/jpeg.c,
ext/axon/jpeg.c

Overview

Read compressed JPEG images from an IO.

Instance Method Summary collapse

Constructor Details

#new(io_in[, markers]) ⇒ Object

Creates a new JPEG Reader. io_in must be an IO-like object that responds to read(size).

markers should be an array of valid JPEG header marker symbols. Valid symbols are :APP0 through :APP15 and :COM.

If performance is important, you can avoid reading any header markers by supplying an empty array, [].

When markers are not specified, we read all known JPEG markers.

io = File.open("image.jpg", "r")
reader = Axon::JPEG::Reader.new(io)

io = File.open("image.jpg", "r")
reader = Axon::JPEG::Reader.new(io, [:APP4, :APP5])



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# File 'ext/axon/jpeg.c', line 601

static VALUE
initialize(int argc, VALUE *argv, VALUE self)
{
    struct readerdata *reader;
    j_decompress_ptr cinfo;
    VALUE io, markers;

    Data_Get_Struct(self, struct readerdata, reader);
    raise_if_locked(reader);
    cinfo = &reader->cinfo;

    rb_scan_args(argc, argv, "11", &io, &markers);

    reader->source_io = io;
    reader->mgr.bytes_in_buffer = 0;

    read_header(reader, markers);

    return self;
}

Instance Method Details

#[](marker) ⇒ Array

Read raw data from the given JPEG header marker. Note that the marker must have been specified by initialize.

The return from this method is an array, since there may be multiple instances of a single marker in a JPEG header.

Returns:

  • (Array) 


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# File 'ext/axon/jpeg.c', line 1015

static VALUE
aref(VALUE self, VALUE marker_sym)
{
    struct jpeg_decompress_struct * cinfo;
    jpeg_saved_marker_ptr marker;
    VALUE ary = rb_ary_new();
    int marker_i = sym_to_marker_code(marker_sym);

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);

    for (marker = cinfo->marker_list; marker != NULL; marker = marker->next)
	if (marker->marker == marker_i)
	    rb_ary_push(ary, rb_str_new(marker->data, marker->data_length));

    return ary;
}

#color_model ⇒ Object

Returns a symbol representing the color model into which the JPEG will be transformed as it is read.

Possible color models are: :GRAYSCALE, :RGB, :YCbCr, :CMYK, and :YCCK. This method will return nil if the color model is not recognized.



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# File 'ext/axon/jpeg.c', line 693

static VALUE
color_model(VALUE self)
{
    ID id;
    struct jpeg_decompress_struct * cinfo;

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);

    id = j_color_space_to_id(cinfo->out_color_space);
    return ID2SYM(id);
}

#color_model=(symbol) ⇒ Object

Explicitly sets the color model to which the JPEG will be transformed as it is read.

Legal transformations are: :YCbCr to :GRAYSCALE, :YCbCr to :RGB, :GRAYSCALE to :RGB, and :YCCK to :CMYK



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# File 'ext/axon/jpeg.c', line 716

static VALUE
set_color_model(VALUE self, VALUE cs)
{
    struct readerdata *reader;

    Data_Get_Struct(self, struct readerdata, reader);
    raise_if_locked(reader);

    reader->cinfo.out_color_space = id_to_j_color_space(SYM2ID(cs));
    return cs;
}

#components ⇒ Numeric

Retrieve the number of components as stored in the JPEG image.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg.c', line 629

static VALUE
components(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return INT2FIX(cinfo->num_components);
}

#dct_method ⇒ Object

Returns a symbol representing the algorithm used for the DCT (discrete cosine transform) step in JPEG encoding.

Possible DCT algorithms are: :ISLOW, :IFAST, and :IFLOAT.



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# File 'ext/axon/jpeg.c', line 822

static VALUE
dct_method(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    ID id;

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);

    id = j_dct_method_to_id(cinfo->dct_method);

    if (NIL_P(id))
	return Qnil;
    else
	return ID2SYM(id);
}

#dct_method=(symbol) ⇒ Object

Sets the algorithm used for the DCT step in JPEG encoding.

Possible DCT algorithms are: :ISLOW, :IFAST, and :IFLOAT.



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# File 'ext/axon/jpeg.c', line 847

static VALUE
set_dct_method(VALUE self, VALUE dct_method)
{
    struct readerdata *reader;
    J_DCT_METHOD val;

    Data_Get_Struct(self, struct readerdata, reader);
    raise_if_locked(reader);

    val = id_to_j_dct_method(SYM2ID(dct_method));
    if (val == (J_DCT_METHOD)NULL) {
	return Qnil;
    } else {
	reader->cinfo.dct_method = val;
	return dct_method;
    }
}

#exif ⇒ String

Get the raw Exif data from the JPEG. This requires that the APP1 segment has been selected by initialize (this is the default behavior).

Returns:

  • (String) 


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# File 'ext/axon/jpeg.c', line 985

static VALUE
exif(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    jpeg_saved_marker_ptr marker;
    int len;

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);

    for (marker = cinfo->marker_list; marker != NULL; marker = marker->next) {
	if (marker_is_exif(marker)) {
	    len = marker->data_length - EXIF_OVERHEAD_LEN;
	    return rb_str_new(marker->data + EXIF_OVERHEAD_LEN, len);
	}
    }

    return Qnil;
}

#gets ⇒ String?

Reads the next scanline of data from the image. Once the first scanline has been read you can no longer change read options for this reader.

If the end of the image has been reached, this will return nil.

Returns:

  • (String, nil) 


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# File 'ext/axon/jpeg.c', line 875

static VALUE
j_gets(VALUE self)
{
    struct readerdata *reader;
    struct jpeg_decompress_struct *cinfo;
    VALUE sl;
    int sl_width, ret;
    JSAMPROW ijg_buffer;

    Data_Get_Struct(self, struct readerdata, reader);
    cinfo = &reader->cinfo;

    if (!reader->header_read)
      read_header(reader, Qnil);

    if (!reader->decompress_started) {
	reader->decompress_started = 1;
	jpeg_start_decompress(cinfo);
    }

    sl_width = cinfo->output_width * cinfo->output_components;
    sl = rb_str_new(0, sl_width);
    ijg_buffer = (JSAMPROW)RSTRING_PTR(sl);

    ret = jpeg_read_scanlines(cinfo, &ijg_buffer, 1);
    return ret == 0 ? Qnil : sl;
}

#height ⇒ Numeric

Retrieve the height of the image as it will be written out. This can be affected by scale_num and scale_denom if they are set.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg.c', line 927

static VALUE
height(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return INT2FIX(cinfo->output_height);
}

#icc_profile ⇒ String

Read the raw icc_profile from the JPEG. This requires that the APP2 segment has been selected by initialize (this is the default behaviour).

Returns:

  • (String) 


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# File 'ext/axon/jpeg.c', line 943

static VALUE
icc_profile(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    JOCTET *icc_embed_buffer;
    unsigned int icc_embed_len;
    VALUE str;

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    read_icc_profile(cinfo, &icc_embed_buffer, &icc_embed_len);

    if (icc_embed_len <= 0) {
	return Qnil;
    } else {
	str = rb_str_new(icc_embed_buffer, icc_embed_len);
	free(icc_embed_buffer);
	return str;
    }
}

#in_color_model ⇒ Object

Returns a symbol representing the color model in which the JPEG is stored.

This does not have to be set explicitly and can be relied upon when the file conforms to JFIF or Adobe conventions. Otherwise it is guessed.

Possible color models are: :GRAYSCALE, :RGB, :YCbCr, :CMYK, and :YCCK. This method will return nil if the color model is not recognized.



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# File 'ext/axon/jpeg.c', line 650

static VALUE
in_color_model(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    ID id;

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    id = j_color_space_to_id(cinfo->jpeg_color_space);

    return ID2SYM(id);
}

#in_color_model=(symbol) ⇒ Object

Explicitly sets the color model the JPEG will be read in. This will override the guessed color model.



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# File 'ext/axon/jpeg.c', line 670

static VALUE
set_in_color_model(VALUE self, VALUE cs)
{
    struct readerdata *reader;

    Data_Get_Struct(self, struct readerdata, reader);
    raise_if_locked(reader);
    reader->cinfo.jpeg_color_space = id_to_j_color_space(SYM2ID(cs));

    return cs;
}

#lineno ⇒ Numeric

Returns the number of the next line to be read from the image, starting at 0.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg.c', line 1070

static VALUE
lineno(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return INT2FIX(cinfo->output_scanline);
}

#saw_adobe_marker ⇒ Boolean

Indicates whether an Adobe marker was found in the header.

Returns:

  • (Boolean) 


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# File 'ext/axon/jpeg.c', line 1054

static VALUE
saw_adobe_marker(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return cinfo->saw_Adobe_marker ? Qtrue : Qfalse;
}

#saw_jfif_marker ⇒ Boolean

Indicates whether a JFIF marker was found in the header.

Returns:

  • (Boolean) 


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# File 'ext/axon/jpeg.c', line 1039

static VALUE
saw_jfif_marker(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return cinfo->saw_JFIF_marker ? Qtrue : Qfalse;
}

#scale_denom ⇒ Numeric

Retrieve the denominator of the fraction by which the JPEG will be scaled as it is read. This is 1, 2, 4, or 8 for libjpeg version 6b. In version 8b this is always the source DCT size, which is 8 for baseline JPEG.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg.c', line 779

static VALUE
scale_denom(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return INT2FIX(cinfo->scale_denom);
}

#scale_denom=(number) ⇒ Object

Set the denominator of the fraction by which the JPEG will be scaled as it is read. This can be set to 1, 2, 4, or 8 for libjpeg version 6b. In version 8b this must always be the source DCT size, which is 8 for baseline JPEG.

Prior to version 1.2, libjpeg-turbo will not scale down images on decompression, and this option will do nothing.



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# File 'ext/axon/jpeg.c', line 799

static VALUE
set_scale_denom(VALUE self, VALUE scale_denom)
{
    struct readerdata *reader;

    Data_Get_Struct(self, struct readerdata, reader);
    raise_if_locked(reader);

    reader->cinfo.scale_denom = NUM2INT(scale_denom);
    jpeg_calc_output_dimensions(&reader->cinfo);
    return scale_denom;
}

#scale_num ⇒ Numeric

Retrieve the numerator of the fraction by which the JPEG will be scaled as it is read. This is always 1 for libjpeg version 6b. In version 8b this can be 1 to 16.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg.c', line 737

static VALUE
scale_num(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return INT2FIX(cinfo->scale_num);
}

#scale_num=(number) ⇒ Object

Set the numerator of the fraction by which the JPEG will be scaled as it is read. This must always be 1 for libjpeg version 6b. In version 8b this can be set to 1 through 16.

Prior to version 1.2, libjpeg-turbo will not scale down images on decompression, and this option will do nothing.



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# File 'ext/axon/jpeg.c', line 757

static VALUE
set_scale_num(VALUE self, VALUE scale_num)
{
    struct readerdata *reader;

    Data_Get_Struct(self, struct readerdata, reader);
    raise_if_locked(reader);

    reader->cinfo.scale_num = NUM2INT(scale_num);
    jpeg_calc_output_dimensions(&reader->cinfo);
    return scale_num;
}

#width ⇒ Numeric

Retrieve the width of the image as it will be written out. This can be affected by scale_num and scale_denom if they are set.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg.c', line 911

static VALUE
width(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);
    return INT2FIX(cinfo->output_width);
}