Class: Axon::PNG::Reader

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

Overview

Read compressed PNG 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 621

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

    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

#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 714

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);
}

#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 650

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

#gets ⇒ String?

Reads the next scanline of data from the image.

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

Returns:

  • (String, nil) 


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# File 'ext/axon/png.c', line 417

static VALUE
p_gets(VALUE self)
{
    struct png_data *reader;
    png_structp png_ptr;
    png_infop info_ptr;
    int width, components, sl_width;
    size_t height;
    VALUE sl;

    Data_Get_Struct(self, struct png_data, reader);
    png_ptr = reader->png_ptr;
    info_ptr = reader->info_ptr;

    height = png_get_image_height(png_ptr, info_ptr);
    if (reader->lineno >= height)
	return Qnil;

    width = png_get_image_width(png_ptr, info_ptr);
    components = get_components(png_ptr, info_ptr);
    sl_width = width * components;

    sl = rb_str_new(0, sl_width);
    png_read_row(png_ptr, (png_bytep)RSTRING_PTR(sl), (png_bytep)NULL);
    reader->lineno += 1;

    if (reader->lineno >= height)
	png_read_end(png_ptr, info_ptr);

    return 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 961

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

#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 1104

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

#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 945

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