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.