PHOTO_READ Function

Reference Guide > P Routines > PHOTO_READ Function

PHOTO_READ Function

Reads image files or a series of image files and returns an image associative array or a list array containing the image associative arrays.

note	The PHOTO routines are only available on 64-bit PV-WAVE.

Usage

image = PHOTO_READ(filename)

Input Parameters

filename — A string or string array containing the pathname and filename of an image file. System variables/logicals and special characters recognized by the operating system shell can be used in the path.

note	If filename is a string array, the Series keyword must be set. For more information on creating a string array containing the names of all files matching a specified file description, please see the FINDFILE Function.

Keywords

All_Subimages — If set, all subimages in the file are read and the Img_Count keyword is ignored. The first subimage in the file is read first, unless the Sub_Img keyword is also specified.

note	Multiple images read with PHOTO_READ must all be of the same height, width, and class. If a file contains images of different heights, widths, and/or classes, use the Sub_Img option to read sub-images one at a time.

File_Type — A string specifying the default file type. Valid values are:

BMP	JPG	PNG	TIF
DICM	MIFF	SUN	XWD
GIF	PCD	TGA	XPM
JPEG	PCX	TIFF	XBM

See the Discussion section for further details about these image types.

Intleave — A scalar string indicating the desired type of interleaving of 3D image arrays. (Default: pixel)

Valid strings and the corresponding interleaving methods are:

'image' or 'plane' — The RGB pixel array arrangement is (x, y, 3) for 3 image-interleaved channels of x-by-y pixels.

'row' or 'line' — The RGB pixel array arrangement is (x, 3, y) for 3 row-interleaved channels of x-by-y pixels.

'pixel' or 'none' — The RGB pixel array arrangement is (3, x, y) for 3 pixel-interleaved channels of x-by-y pixels.

Img_Count — An integer specifying the number of images to read from an array of images.

note	The Img_Count keyword is ignored if the All_Subimages keyword is set.

Invalid — (Output) Returns a PV-WAVE variable indicating success or failure when reading a set of images with the Series keyword.

Possible values are:

–1 — All images successfully read.

INT array — One or more images could not be read. The INT array contains the indices of the unread images in the returned LIST of images.

Quiet — Suppresses successive levels of error messages, depending on the value set. This keyword accepts the same integer values used with the system variable !Quiet.

ROI — Array, specifying the region of interest, in pixels, to extract from an image file. ROI = [x_pos, y_pos, num_x, num_y]

Series — If set, PHOTO_READ returns a list array containing the image associative arrays matching the string array input for filename. Images in the string array must be of the same width, height, and class.

Sub_Img — The index number (integer) of the first image to read from an array of images. (Default: 0, the first image)

note	If Sub_Img is used to request a subimage that is not in the image file, the status key of the returned image associative array is set to a negative number.

Verbose — If nonzero, any available information about the file is printed to the screen.

Returned Value

image — An image associative array or a list of image associative arrays. The status field contains a value indicating the success or failure of the function.

< 0 — Indicates an error reading the file or a bad file type.

0 — Indicates a successful read.

Discussion

Refer to the PHOTO_CREATE Function for detailed information on the structure of the image associative array.

note	When you read a DICOM file with PHOTO_READ, PV-WAVE converts the hexadecimal DICOM tags to a human-readable format and stores them in a string array in the ’comments’ key with the format (####,####) Value.

File Name Formats for PHOTO lists the file formats that you can read and write using PHOTO_READ and PHOTO_WRITE functions, respectively.

Table 13-4: File Name Formats for PHOTO
File type	Read/Write	Notes
BMP	RW	The BMP format currently supported for writing is version 4.
DICM	RW	Uses Sub_Img option to read sub-images one at a time. Files read with the .dcm extension will have the File_Type set to 'DICM'.
GIF	RW
JPEG* JPG	RW	If your image associative array does not contain a colormap, the 2D image pixel array is preserved and a greyscale color map is added.
MIFF	RW
PCD	R
PCX	RW
PNG	RW
SUN	RW
TGA	RW
TIFF TIF	RW
XWD	RW	Not supported on Windows.
XPM	R	Not supported on Windows. Converted to 24-bit direct color on read/write. (NOTE: In order to read an XPM file, the DISPLAY environment variable must be set.)
XBM	R	Reduces the image to monochrome (black and white) on write.
* PV-WAVE is based in part on the work of the Independent JPEG Group.

Most image files have an encoded ID number to identify the file format. When PHOTO_READ reads an image file, it determines the type of file according to the rules of precedence used by the function PHOTO_QUERY_FILE.

note	File type TGA does not have an encoded ID number. To read this type of file you must specify the File_type keyword or filename must have a .tga suffix.

If at least the first requested subimage in the image file is available, but the number of requested images exceeds the highest subimage number in the file, a warning message is displayed and the number of images in the file is returned in the img_count key of the returned image associative array.

When you read a DICOM file with PHOTO_READ, PV-WAVE converts the DICOM tags to a human-readable format and stores them in a string array in the ’comments’ key with the format (####,####) Value. PV-WAVE converts this string array back, updating the default DICOM tags to match the current status of the image, when you write the image with the PHOTO_WRITE Function.

Example 1

; Reads the file teluride24.jpg and returns an

; image associative array.

 teluride = PHOTO_READ(!Dir + '/demo/gallery3/data/teluride24.jpg')

Example 2

; Reads the sorted series of files IM-0042-*.tif in the

; data directory. Returns a list array containing the

; image associative arrays.

CD, !Dir + '/demo/gallery3/data/', Current=curr_dir

filenames = FINDFILE('IM-0042*.tif')

filenames = SORTDIM(filenames,0)

image = PHOTO_READ(filenames, /Series)

CD, curr_dir

Example 3

; Reads and displays the series of files IM-0042-*.tif in the

; data directory. Returns a list array containing the image

; associative arrays and displays the reversed results

; with a 0.5 second frame-to-frame delay.

CD, !Dir + '/demo/gallery3/data/', Current=curr_dir

filenames = FINDFILE('IM-0042*.tif')

filenames = REVERSE(SORTDIM(filenames,0), 1)

image = PHOTO_READ(filenames, /Series)

CD, curr_dir

PHOTO_DISPLAY, image, /Series, Delay=0.5

Example 4

; This example demonstrates the use of the Invalid keyword to

; identify and locate images which were not successfully read.

CD, !Dir + '/demo/gallery3/data/', Current=curr_dir

filenames = FINDFILE('IM-0042*.tif')

filenames = REVERSE(SORTDIM(filenames,0), 1)

image = PHOTO_READ(filenames, /Series, Invalid=outvar)

; All the images were read successfully so Invalid returns a -1.

INFO, outvar

; PV-WAVE prints:

; OUTVAR INT = -1

; Put two unreadable files in the list of filenames at positions 4

; and 7.

filenames(4) = "doesntExist.tif"

filenames(7) = "doesntExistEither.tif"

image = PHOTO_READ(filenames, /Series, Invalid=outvar, Quiet=3)

INFO, outvar & PM, outvar

; PV-WAVE prints

; OUTVAR INT = Array(2)

;      4

;      7

INFO, /Full, image(outvar)

; PV-WAVE prints

; <Expression> LIST = List(2)

;      AS. ARR = Associative Array(2)

;           status LONG = -9

;           comments STRING = 'Unable to read file: doesntExist.tif'

;      AS. ARR = Associative Array(2)

;           status LONG = -9

;          comments STRING = 'Unable to read file: doesntExistEither.tif'

Example 5

; Reads the file dna.miff and returns an

; image associative array with a ROI extracted.

dna = PHOTO_READ(!Dir + '/demo/gallery3/data/dna.miff', ROI=[600,400,100,100])