class FreeImage::Scanline

  1. lib/free-image/scanline.rb
Superclass: Object

Summary ↑

Scanlines provide low level access to image data. The only lower-level access is working with the actual raw bytes, which you can do via the FreeeImage::Bitmap#bytes method, but its not recommended.

A scanline represents one row of image data, starting from the bottom. You can get a scanline via the Freeimage::Pixels#scanline method.

To understand how scanlines work, you have to first understand that image data is stored differently depending on the image type and the bits per pixel. Thus, when you call reeImage::Scanline#[] with an index, you will get back a different object depending on the image type and bit depth.

In a :bitmap image, possible bit depths are 1-, 4-, 8-, 16-, 24-, 32-, 48-, 64-, 96- and 128-bit.

  • 1-bit DIBs are stored using each bit as an index into the color table. The most significant bit is the leftmost pixel. This is not currently supported.

  • 4-bit DIBs are stored with each 4 bits representing an index into the color table. The most significant nibble is the leftmost pixel. This is not currently supported.

  • 8-bit DIBs are the easiest to store because each byte is an index into the color table. This is not currently supported.

  • 24-bit DIBs have every 3 bytes representing a color, using the same ordering as the RGBTRIPLE structure. Colors are represented using FreeImage::RGBTriple.

  • 32-bit DIB have every 4 bytes representing a color associated to a alpha value (used to indicate transparency). Colors are represented using FreeImage::RGBTriple.

Non standard image types such as short, long, float or double do not have a color table. Pixels are stored in a similar way as 8-bit DIB.

Complex image types are stored in a similar way as 24- or 32bit DIB. Colors are represented using FreeImage::Complex.

16-bit RGB image types are stored in a similar way as 24-bit DIBs. Colors are represented using FreeImage::RGB16 or FreeImage::RFBA16.

Float RGB image types are stored in a similar way 32bit DIBs. Colors are represented using FreeImage::RGBF or FreeImage::RFBAF.

Methods

Public Class

  1. new

Public Instance

  1. []
  2. bytesize
  3. each
  4. pixelsize

Included modules

  1. Enumerable

Public Class methods

new (bitmap, index, ptr)

Creates a new scanline instance

Parameters ↑

bitmap

An instance of FreeImage::Bitmap

index

The index of the scanline, must be between 0 and the image pixel heigh minus one.

ptr

A pointer to the raw pixel data.

Generally you do not want to call this method directly. Instead, use FreeImage::Pixels#scanline.

[show source] 
# File lib/free-image/scanline.rb, line 59
def initialize(bitmap, index, ptr)
  @bitmap = bitmap
  @index = index
  @ptr = ptr
end

Public Instance methods

[] (index)

Returns the appropriate color object for the image type and bit depth. See notes for the FreeImage::Scanline class.

Parameters ↑

index

The index of the scanline, must be between 0 and the image pixel width minus one.

Returns the appropriate object for manipulating the data.

[show source] 
# File lib/free-image/scanline.rb, line 74
def [](index)
  unless (0...pixelsize).include?(index)
    raise(RangeError, "Index must be between 0 and #{pixelsize - 1}")
  end
  bytes_per_pixel = @bitmap.bits_per_pixel/8

  # Now get the address of the pixel
  address = @ptr.address + (index * bytes_per_pixel)

  # Now get a pointer to the pixel
  ptr = FFI::Pointer.new(bytes_per_pixel, address)

  # Now return a nice object to work with
  color_type.new(ptr)
end
bytesize ()

The width of the image in bytes. Same as FreeImage::Information#pitch.

[show source] 
# File lib/free-image/scanline.rb, line 98
def bytesize
  @bitmap.pitch
end
each ()

Iterate over each pixel, returning the appropriate object to manipulate the underlying data.

[show source] 
# File lib/free-image/scanline.rb, line 105
def each
  pixelsize.times do |i|
    yield (self[i])
  end
end
pixelsize ()

The width of the image in pixels. Same as FreeImage::Information#width.

[show source] 
# File lib/free-image/scanline.rb, line 92
def pixelsize
  @bitmap.width
end