WRITE_PNG
Syntax | Arguments | Keywords | Examples | Version History | See Also
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.
Note
IDL supports version 1.2.7 of the PNG Library.
Syntax
WRITE_PNG, Filename, Image[, R, G, B] [, /ORDER] [, /VERBOSE] [, TRANSPARENT=array]
Arguments
Filename
A scalar string containing the full pathname of the PNG file to write.
Image
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.
Note
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.
R, G, B
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.
Keywords
ORDER
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.
VERBOSE
Produces additional diagnostic output during the write.
TRANSPARENT
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.
Examples
The following lines create an image in an IDL graphics window, read it from the window and write it as a .png file in the temporary directory, then read the .png file and display it in the same graphics window:
Version History
![; Save device settings and tell IDL to use a color table DEVICE, GET_DECOMPOSED=old_decomposed DEVICE, DECOMPOSED=0 LOADCT, 14 ; Create an image and display it IMAGE1 = DIST(300) WINDOW, 1, XSIZE=300, YSIZE=300 TV, IMAGE1 ; Write a PNG file to the temporary directory ; Note the use of the TRUE keyword to TVRD filename = FILEPATH('test.png', /TMP) WRITE_PNG, filename, TVRD(/TRUE) PRINT, 'File written to ', filename ; Read in the file IMAGE2 = READ_PNG(filename) ; Display the IMAGE1 and IMAGE2 side by side ; Note the use of the TRUE keyword to TV WINDOW, 1, XSIZE=600, YSIZE=300, $ TITLE='Original (left) and Image read from file (right)' TV, IMAGE1, 0 TV, IMAGE2, 1, /TRUE ; Restore device settings. DEVICE, DECOMPOSED=old_decomposed](javascript:doIDL("; Save device settings and tell IDL to use a color table\nDEVICE, GET_DECOMPOSED=old_decomposed\nDEVICE, DECOMPOSED=0\nLOADCT, 14\n\n; Create an image and display it\nIMAGE1 = DIST(300)\nWINDOW, 1, XSIZE=300, YSIZE=300\nTV, IMAGE1\n\n; Write a PNG file to the temporary directory\n; Note the use of the TRUE keyword to TVRD\nfilename = FILEPATH('test.png', /TMP)\nWRITE_PNG, filename, TVRD(/TRUE)\nPRINT, 'File written to ', filename\n\n; Read in the file\nIMAGE2 = READ_PNG(filename)\n\n; Display the IMAGE1 and IMAGE2 side by side\n; Note the use of the TRUE keyword to TV\nWINDOW, 1, XSIZE=600, YSIZE=300, $\n TITLE='Original (left) and Image read from file (right)'\nTV, IMAGE1, 0\nTV, IMAGE2, 1, /TRUE\n\n; Restore device settings.\nDEVICE, DECOMPOSED=old_decomposed")){kind=link}