How to read multiband envi file into matlab?

I am using the following matlab syntex to read envi generated image file;

img_path = 'C:\Data\'

d = uigetdir(pwd, 'Select a folder');

imgfiles = dir(fullfile(d, '*.img'));

for m = 1:length(imgfiles)

img_file = imgfiles(m);

disp(img_file.name);

img = imread(img_file.name);

red = img(:,:,4); % red band

rededge1 = img(:,:,5); % rededge1 band

rededge2 = img(:,:,6); % rededge2 band

rededge3 = img(:,:,7); % rededge3 band

nir = img(:,:,8); % near infrared band

This code is giving following errors

>> ds_indices_caf

img_path =

'C:\Data\'

20240309_SAMPLE_DATA.img

Error using imread>get_full_filename

File "20240309_SAMPLE_DATA.img" does not exist.

Error in imread (line 372)

fullname = get_full_filename(filename);

Error in ds_indices_caf (line 17)

img = imread(img_file.name);

>>

I am attaching the input file as zip file. Please suggest me how to fix this error.

Deva

Answer 1

[Manasa Singam]

The imread function can't read ENVI format files (.img and .hdr). Use the multibandread function and specify the required inputs.

For examplem, for the above data, the command will be:

>> ImgFilename = "20240309_SAMPLE_DATA.img";

>> size = [399 426 7];

>> datatype = "uint16"; % uint16 for 12

>> headerOffset = 0;

>> interleave = "bsq";

>> byteOrder = "ieee-le"; % 0 means little-endian

>> data = multibandread(ImgFilename,size,datatype,headerOffset,interleave,byteOrder);

But i suggest to use hypercube function, which supports to read envi format files. https://in.mathworks.com/matlabcentral/fileexchange/76796-image-processing-toolbox-hyperspectral-imaging-library

hypercube(ImgFilename);

[Devendra]

problem is in next session.

[Devendra]

Now I am using hypercube function as follows

img = hypercube(img_file.name);

red = img(:,:,2); % red band

rededge1 = img(:,:,3); % rededge1 band

rededge2 = img(:,:,4); % rededge2 band

rededge3 = img(:,:,5); % rededge3 band

nir = img(:,:,6); % near infrared band

it still gives following errors.

>> ds_indices_caf

img_path = 'C:\Data\'

20240129_MAWANA_SUBSET.img

hypercube with properties:

DataCube: "[3915x3677x7 uint16]"

Wavelength: [7×1 double]

Metadata: [1×1 struct]

Index in position 3 exceeds array bounds. Index must not exceed 1.

Error in ds_indices_caf (line 25)

red = img(:,:,2); % red band

Please suggest me how to fix it.

Dave

[Manasa Singam]

Here the variable "img" is hypercube object. The data is present in DataCube property.

Access the data using this command: red = img.DataCube(:,:,2);

[Devendra]

Thanks a lot for your kind help. I am getting integer numbers. How to convert them into real number in matlab?

Dave

[Manasa Singam]

if you are refering to single and double class data types by real number, then you can directly convert data type using: single(red) or double(red).

[Devendra]

Actulally I am computing NDVI as follows

NDVI = (nir - red) ./ (nir + red);

Here I am getting either 0 or 1 values not real numbers up to four decimal numbers. Since red and nir both contains integer numbers. I want NDVI values as real numbers. Please suggest me how to do it?

I am thankful to you for providing me support.

Deva

[Manasa Singam]

You can convert to single data type.

data = single(img.DataCube);

Use data numeric array which is in single data type to caculate NDVI.

red = data(:,:,4);

nir = data(:,:,8);

But i suggest you to use ndvi function which is available in the downloaded hyperspectral package itself. It will directly take hypercube object and will give you the ndvi image.

If the HDR file doesn't contain wavelength values in it, make sure it give proper ranges fo red and nir. Red ranges from 610-700nm and NIR ranges from 700-1400nm.