The READ_BMP function reads a Microsoft Windows Version 3 device independent bitmap file (.BMP) and returns the image.
READ_BMP does not handle 1-bit-deep images or compressed images, and is not fast for 4-bit images. The algorithm works best on images where the number of bytes in each scan-line is evenly divisible by 4.
This routine is written in the IDL language. Its source code can be found in the file
read_bmp.pro in the
lib subdirectory of the IDL distribution.
Result = READ_BMP( Filename, [, R, G, B] [, Ihdr] [, /RGB] )
Returns a byte array containing the image. Dimensions are taken from the BITMAPINFOHEADER of the file. In the case of 4-bit or 8-bit images, the dimensions of the resulting array are (
For 24-bit images, the dimensions are (
biHeight). Color interleaving is blue, green, red; i.e., Result[0,i,j] = blue, Result[1,i,j] = green, etc.
A scalar string specifying the full path name of the bitmap file to read.
Named variables that will contain the color tables from the file. There 16 elements each for 4 bit images, 256 elements each for 8 bit images. Color tables are not defined or used for 24 bit images.
A named variable that will contain a structure holding the BITMAPINFOHEADER from the file. Tag names are as defined in the MS Windows Programmer's Reference Manual, Chapter 7.
If this keyword is set, color interleaving of 16- and 24-bit images will be R, G, B, i.e., Result[0,i,j] = red, Result[1,i,j] = green, Result[2,i,j] = blue.
To open, read, and display the BMP file named
foo.bmp in the current directory and store the color vectors in the variables R, G, and B, enter:
; Read and display an image: TV, READ_BMP('foo.bmp', R, G, B) ; Load its colors: TVLCT, R, G, B
Many applications that use 24-bit BMP files outside IDL expect BMP files to be stored as BGR. For example, enter the following commands.
; Make a red square image: a = BYTARR(3, 200, 200) a[0, *, *] = 255 ;View the image: TV, a, /TRUE WRITE_BMP, 'foo.bmp', a
If you open the
.bmp file in certain bitmap editors, you may find that the square is blue.
image = READ_BMP('foo.bmp') ; IDL reads the image back in and interprets it as red: TV, image, /TRUE ; Flip the order of the indices by adding the RGB keyword: image = READ_BMP('foo.bmp', /RGB) ; Displays the image in blue: TV, image, /TRUE
Introduced: Pre 4.0