Class: Axon::JPEGReader

Inherits:
Object
  • Object
show all
Includes:
Image, Enumerable
Defined in:
ext/axon/jpeg_reader.c

Instance Method Summary collapse

Methods included from Image

#crop, #fit, #scale_bilinear, #scale_nearest_neighbor, #to_jpeg, #to_png, #write_jpeg, #write_png

Constructor Details

#new(io[, markers, rewind_after_scanlines]) ⇒ Object

Create a new JPEG Reader. string_or_io may be an object that responds to read or a string.

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 all header markers by supplying an empty array, [].

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



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# File 'ext/axon/jpeg_reader.c', line 185

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

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

    rb_scan_args(argc, argv, "12", &io, &markers, &rewind_after_scanlines);

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

    if(NIL_P(markers)) {
	jpeg_save_markers(cinfo, JPEG_COM, 0xFFFF);

	for (i = 0; i < 16; i++)
	    jpeg_save_markers(cinfo, JPEG_APP0 + i, 0xFFFF);
    }

    reader->rewind_after_scanlines = RTEST(rewind_after_scanlines);
    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 Reader#save_markers prior to the call to Reader#read_header.

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_reader.c', line 680

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 space into which the JPEG will be transformed as it is read.

By default this color space is based on Reader#color_space.

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



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# File 'ext/axon/jpeg_reader.c', line 286

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 space 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_reader.c', line 308

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;
}

#num_components ⇒ Numeric

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

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg_reader.c', line 221

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_reader.c', line 428

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.



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# File 'ext/axon/jpeg_reader.c', line 450

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;
    }
}

#each_scanline(&block) ⇒ Object

Iterate over each decoded scanline in the JPEG image. During this operation the reader is locked, and you can’t change any decoding parameters or re initialize the reader.

Should a major exception occur (anything other than a StandardError), then the reader will be left in a locked state.



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# File 'ext/axon/jpeg_reader.c', line 542

static VALUE
each(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;
    struct readerdata *reader;

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

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

    reader->locked = 1;
    jpeg_start_decompress(&reader->cinfo);

    rb_ensure(each2, (VALUE)reader, each2_ensure, (VALUE)reader);

    return self;
}

#exif ⇒ String

Read the Exif data from the JPEG. This requires that the APP1 segment has been selected by save_markers (this is the default behaviour).

Returns:

  • (String) 


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

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;
}

#height ⇒ Numeric

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

Note that this value is not automatically calculated unless you call Reader#calc_output_dimensions or after Reader#each_scanline has been called.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg_reader.c', line 592

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

Returns:

  • (String) 


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# File 'ext/axon/jpeg_reader.c', line 609

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



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# File 'ext/axon/jpeg_reader.c', line 243

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);
}

#color_space=(symbol) ⇒ Object

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



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# File 'ext/axon/jpeg_reader.c', line 262

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;
}

#saw_adobe_marker ⇒ Boolean

Indicate that an Adobe marker was found in the header.

Returns:

  • (Boolean) 


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# File 'ext/axon/jpeg_reader.c', line 719

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

Indicate that a JFIF marker was found in the header.

Returns:

  • (Boolean) 


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# File 'ext/axon/jpeg_reader.c', line 703

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_reader.c', line 366

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.



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# File 'ext/axon/jpeg_reader.c', line 384

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 = FIX2INT(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_reader.c', line 328

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.



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# File 'ext/axon/jpeg_reader.c', line 345

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 = FIX2INT(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 is primarily affected by scale_num and scale_denom if they are set.

Note that this value is not automatically calculated unless you call Reader#calc_output_dimensions or after Reader#each_scanline has been called.

Returns:

  • (Numeric) 


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# File 'ext/axon/jpeg_reader.c', line 572

static VALUE
width(VALUE self)
{
    struct jpeg_decompress_struct * cinfo;

    Data_Get_Struct(self, struct jpeg_decompress_struct, cinfo);

    return INT2FIX(cinfo->output_width);
}