For loop for many images

Hi All,

I have thousands of images each image has size (228*196), Each 7 images have same date. I need your help to create a code to do calculation which is (7th image - 2nd image)/(7th image + 2nd image).. I want to do that for each date.

Thank you

Reyadh

[Walter Roberson]

How can you determine the date based on the file name? How can you determine which is the 2nd or 7th image based on the file name?

[per isakson]

See question: https://uk.mathworks.com/matlabcentral/answers/333634-how-to-create-for-loop-in-matlab

[reyadh Albarakat]

Hi Walter Roberson,

yes there is a date and the band number here is the example:

((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b01_clip.tif_mosaico_ream.tif)) ((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b02_clip.tif_mosaico_ream.tif)) ((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b03_clip.tif_mosaico_ream.tif)) ((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b04_clip.tif_mosaico_ream.tif)) ((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b05_clip.tif_mosaico_ream.tif)) ((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b06_clip.tif_mosaico_ream.tif)) ((MOD09A1. A2000057.h21v05.006.2015136062042.hdf_sur_refl_ b07_clip.tif_mosaico_ream.tif))

Answer 1

[Walter Roberson]

dinfo = dir('*_b02_clip.tif_mosaico_ream.tif');
nfile = length(dinfo);
filenames = {dinfo.name};
for K = 1 : nfile
  b2_file = filenames{K};
  b7_file = b2_file; b7_file(end-27) = '7';
  b2_data = double( imread(b2_file) );
  b7_data = double( imread(b7_file) );
  result = (b7_data - b2_data) ./ (b7_data + b2_data);
  %now what?
end

[reyadh Albarakat]

Thank you Walter for reply

I got this error

((Error using imread))

is this loop for all date?. As I said each date has 7 bands, this date which A2000057 (year:2000 day:57) and next 8 days has new 7 bands like this

((MOD09A1. A2000065.h21v05.006.2015136062016.hdf_sur_refl_ b01_clip.tif_mosaico_ream.tif))

So this continue from 2000057 (year:2000 day:57) to A2016217 (year:2016 day:217).

Is it clear now?

[Walter Roberson]

It looks like my (end-27) should be (end-26)

However, if the file name includes literal '(' or ')' or '*' characters then the count will need to be adjusted at the very least, and I am not certain imread() would be able to read files with those in the name. Possibly it could on OS-X or Linux.

[reyadh Albarakat]

Hi Walter, By the way I got b2_data matrix (228*196) Why you used (end-27)? this numbers don't represent the date. the numbers that represents the data for images is A2000057 (year:2000 day:57) and A2000065 (year:2000 day:65) till A2016217 (year:2016 day:217)

[Walter Roberson]

I am not specifically advancing by date. You asked that the 7th image for each date be manipulated against the 2nd image for each date. I handle that by searching for all of the 2nd images (the b02 files), and for each one encountered, replace the 'b02' with 'b07'.

To generalize a little:

dinfo = dir('*_b02_clip.tif_mosaico_ream.tif');
nfile = length(dinfo);
filenames = {dinfo.name};
for K = 1 : nfile
  b2_file = filenames{K};
  band_pos = strfind(b2_file, '_b02');
  b7_file = b2_file; b7_file(band_pos + 3) = '7';
  b2_data = double( imread(b2_file) );
  b7_data = double( imread(b7_file) );
  result = (b7_data - b2_data) ./ (b7_data + b2_data);
  %now what?
end

[reyadh Albarakat]

Hi Walter,

Now it works BUT with only one data NOT for all dates.

Please Walter could you complete your help to make it a loop for all dates

I appreciate your efforts

Thank you

Reyadh

[Walter Roberson]

It already loops over all dates, provided that the band 2 files all end in b02_clip.tif_mosaico_ream.tif

If not then you could perhaps use

dinfo = dir('*_b02_*.tif');

If the b02 part is not consistent then you need to be clearer as to how you can recognize the band number.