Method Image.JPEG.decode_header()

Method decode_header

object decode(string data)
object decode(string data, mapping options)
mapping _decode(string data)
mapping _decode(string data, mapping options)
mapping decode_header(string data)

Description

Decodes a JPEG image. The simple decode function simply gives the image object, the other functions gives a mapping of information (see below).

The options argument may be a mapping containing zero or more decoding options:

"block_smoothing" : bool	Do interblock smoothing. Default is on (1).
"fancy_upsampling" : bool	Do fancy upsampling of chroma components. Default is on (1).
"method" : int	DCT method to use. Any of IFAST, ISLOW, FLOAT, DEFAULT or FASTEST. DEFAULT and FASTEST is from the jpeg library, probably ISLOW and IFAST respective.
"scale_num" : int(1..)	Rescale the image when read from JPEG data. My (Mirar) version (6a) of jpeglib can only handle 1/1, 1/2, 1/4 and 1/8.
"scale_denom" : int(1..)

_decode and decode_header gives a mapping as result, with this content:

"comment" : string	Comment marker of JPEG file, if present.
"xsize" : int	Size of image
"ysize" : int
"xdpi" : float	Image dpi, if known.
"ydpi" : float
"type" : string	File type information as MIME type. Always "image/jpeg".
"num_compontents" : int	Number of channels in JPEG image.
"color_space" : string	Color space of JPEG image. Any of "GRAYSCALE", "RGB", "YUV", "CMYK", "YCCK" or "UNKNOWN".
"density_unit" : int(0..2)	The unit used for x_density and y_density. 0 No unit 1 dpi 2 dpcm
"x_density" : int	Density of image.
"y_density" : int
"adobe_marker" : bool	If the file has an Adobe marker.
"quant_tables" : mapping(int:array(array(int)))	JPEG quant tables.
"quality" : int(0..100)	JPEG quality guess.
"marker" : mapping(int(8bit):string(8bit)|array(string(8bit)))	Mapping from application and comment markers to their values.