|IDL Reference Guide: Procedures and Functions|
The WRITE_PNG procedure writes a 2-D or 3-D IDL variable into a Portable Network Graphics (PNG) file. The data in the file is stored using lossless compression with either 8 or 16 data bits per channel, based on the input IDL variable type. 3-D IDL variables must have the number of channels as their leading dimension (pixel interleaved). For BYTE format 2-D IDL variables, an optional palette may be stored in the image file along with a list of pixel values which are to be considered transparent by a reading program.
IDL supports version 1.2.7 of the PNG Library.
WRITE_PNG, Filename, Image[, R, G, B] [, /ORDER] [, /VERBOSE] [, TRANSPARENT=array]
A scalar string containing the full pathname of the PNG file to write.
The array to write into the new PNG file. If Image is one of the integer data types, it is converted to type unsigned integer (UINT) and written out at 16 data bits per channel. All other data types are converted to bytes and written out at 8-bits per channel.
If Image is two-dimensional (single-channel) and R, G, and B are provided, all input data types (including integer) are converted to bytes and written out as 8-bit data.
For single-channel images, R, G, and B should contain the red, green, and blue color vectors, respectively. For multi-channel images, these arguments are ignored.
Set this keyword to indicate that the rows of the image should be written from bottom to top. The rows are written from top to bottom by default. ORDER provides compatibility with PNG files written using versions of IDL prior to IDL 5.4, which wrote PNG files from bottom to top.
Produces additional diagnostic output during the write.
Set this keyword to an array of pixel index values which are to be treated as "transparent" for the purposes of image display. This keyword is valid only if Image is a single-channel (color indexed) image and the R, G, B palette is provided.
Create an RGBA (16-bits/channel) and a Color Indexed (8-bits/channel) image with a palette.
rgbdata = UINDGEN(4,320,240) cidata = BYTSCL(DIST(256)) red = INDGEN(256) green = INDGEN(256) blue = INDGEN(256) WRITE_PNG,'rgb_image.png',rgbdata WRITE_PNG,'ci_image.png',cidata,red,green,blue ; Query and Read the data: names = ['rgb_image.png','ci_image.png','unknown.png'] FOR i=0,N_ELEMENTS(names)-1 DO BEGIN ok = QUERY_PNG(names[i],s) IF (ok) THEN BEGIN HELP,s,/STRUCTURE IF (s.HAS_PALETTE) THEN BEGIN img = READ_PNG(names[i],rpal,gpal,bpal) HELP,img,rpal,gpal,bpal ENDIF ELSE BEGIN img = READ_PNG(names[i]) HELP,img ENDELSE ENDIF ELSE BEGIN PRINT,names[i],' is not a PNG file' ENDELSE ENDFOR
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