def apply(self):
        # Initialization
        fname_src = self.input_filename  # source image (moving)
        list_warp = self.list_warp  # list of warping fields
        fname_out = self.output_filename  # output
        fname_dest = self.fname_dest  # destination image (fix)
        verbose = self.verbose
        remove_temp_files = self.remove_temp_files
        crop_reference = self.crop  # if = 1, put 0 everywhere around warping field, if = 2, real crop

        interp = sct.get_interpolation('isct_antsApplyTransforms', self.interp)

        # Parse list of warping fields
        sct.printv('\nParse list of warping fields...', verbose)
        use_inverse = []
        fname_warp_list_invert = []
        # list_warp = list_warp.replace(' ', '')  # remove spaces
        # list_warp = list_warp.split(",")  # parse with comma
        for idx_warp, path_warp in enumerate(self.list_warp):
            # Check if this transformation should be inverted
            if path_warp in self.list_warpinv:
                use_inverse.append('-i')
                # list_warp[idx_warp] = path_warp[1:]  # remove '-'
                fname_warp_list_invert += [[
                    use_inverse[idx_warp], list_warp[idx_warp]
                ]]
            else:
                use_inverse.append('')
                fname_warp_list_invert += [[path_warp]]
            path_warp = list_warp[idx_warp]
            if path_warp.endswith((".nii", ".nii.gz")) \
             and Image(list_warp[idx_warp]).header.get_intent()[0] != 'vector':
                raise ValueError("Displacement field in {} is invalid: should be encoded" \
                 " in a 5D file with vector intent code" \
                 " (see https://nifti.nimh.nih.gov/pub/dist/src/niftilib/nifti1.h" \
                 .format(path_warp))
        # need to check if last warping field is an affine transfo
        isLastAffine = False
        path_fname, file_fname, ext_fname = sct.extract_fname(
            fname_warp_list_invert[-1][-1])
        if ext_fname in ['.txt', '.mat']:
            isLastAffine = True

        # check if destination file is 3d
        if not sct.check_if_3d(fname_dest):
            sct.printv('ERROR: Destination data must be 3d')

        # N.B. Here we take the inverse of the warp list, because sct_WarpImageMultiTransform concatenates in the reverse order
        fname_warp_list_invert.reverse()
        fname_warp_list_invert = functools.reduce(lambda x, y: x + y,
                                                  fname_warp_list_invert)

        # Extract path, file and extension
        path_src, file_src, ext_src = sct.extract_fname(fname_src)
        path_dest, file_dest, ext_dest = sct.extract_fname(fname_dest)

        # Get output folder and file name
        if fname_out == '':
            path_out = ''  # output in user's current directory
            file_out = file_src + '_reg'
            ext_out = ext_src
            fname_out = os.path.join(path_out, file_out + ext_out)

        # Get dimensions of data
        sct.printv('\nGet dimensions of data...', verbose)
        img_src = Image(fname_src)
        nx, ny, nz, nt, px, py, pz, pt = img_src.dim
        # nx, ny, nz, nt, px, py, pz, pt = sct.get_dimension(fname_src)
        sct.printv(
            '  ' + str(nx) + ' x ' + str(ny) + ' x ' + str(nz) + ' x ' +
            str(nt), verbose)

        # if 3d
        if nt == 1:
            # Apply transformation
            sct.printv('\nApply transformation...', verbose)
            if nz in [0, 1]:
                dim = '2'
            else:
                dim = '3'
            sct.run([
                'isct_antsApplyTransforms', '-d', dim, '-i', fname_src, '-o',
                fname_out, '-t'
            ] + fname_warp_list_invert + ['-r', fname_dest] + interp,
                    verbose=verbose,
                    is_sct_binary=True)

        # if 4d, loop across the T dimension
        else:
            dim = '4'
            path_tmp = sct.tmp_create(basename="apply_transfo",
                                      verbose=verbose)

            # convert to nifti into temp folder
            sct.printv(
                '\nCopying input data to tmp folder and convert to nii...',
                verbose)
            img_src.save(os.path.join(path_tmp, "data.nii"))
            sct.copy(fname_dest, os.path.join(path_tmp, file_dest + ext_dest))
            fname_warp_list_tmp = []
            for fname_warp in list_warp:
                path_warp, file_warp, ext_warp = sct.extract_fname(fname_warp)
                sct.copy(fname_warp,
                         os.path.join(path_tmp, file_warp + ext_warp))
                fname_warp_list_tmp.append(file_warp + ext_warp)
            fname_warp_list_invert_tmp = fname_warp_list_tmp[::-1]

            curdir = os.getcwd()
            os.chdir(path_tmp)

            # split along T dimension
            sct.printv('\nSplit along T dimension...', verbose)

            im_dat = Image('data.nii')
            im_header = im_dat.hdr
            data_split_list = sct_image.split_data(im_dat, 3)
            for im in data_split_list:
                im.save()

            # apply transfo
            sct.printv('\nApply transformation to each 3D volume...', verbose)
            for it in range(nt):
                file_data_split = 'data_T' + str(it).zfill(4) + '.nii'
                file_data_split_reg = 'data_reg_T' + str(it).zfill(4) + '.nii'

                status, output = sct.run([
                    'isct_antsApplyTransforms',
                    '-d',
                    '3',
                    '-i',
                    file_data_split,
                    '-o',
                    file_data_split_reg,
                    '-t',
                ] + fname_warp_list_invert_tmp + [
                    '-r',
                    file_dest + ext_dest,
                ] + interp,
                                         verbose,
                                         is_sct_binary=True)

            # Merge files back
            sct.printv('\nMerge file back...', verbose)
            import glob
            path_out, name_out, ext_out = sct.extract_fname(fname_out)
            # im_list = [Image(file_name) for file_name in glob.glob('data_reg_T*.nii')]
            # concat_data use to take a list of image in input, now takes a list of file names to open the files one by one (see issue #715)
            fname_list = glob.glob('data_reg_T*.nii')
            fname_list.sort()
            im_out = sct_image.concat_data(fname_list, 3, im_header['pixdim'])
            im_out.save(name_out + ext_out)

            os.chdir(curdir)
            sct.generate_output_file(
                os.path.join(path_tmp, name_out + ext_out), fname_out)
            # Delete temporary folder if specified
            if int(remove_temp_files):
                sct.printv('\nRemove temporary files...', verbose)
                sct.rmtree(path_tmp, verbose=verbose)

        # Copy affine matrix from destination space to make sure qform/sform are the same
        sct.printv(
            "Copy affine matrix from destination space to make sure qform/sform are the same.",
            verbose)
        im_src_reg = Image(fname_out)
        im_src_reg.copy_qform_from_ref(Image(fname_dest))
        im_src_reg.save(
            verbose=0
        )  # set verbose=0 to avoid warning message about rewriting file

        # 2. crop the resulting image using dimensions from the warping field
        warping_field = fname_warp_list_invert[-1]
        # if last warping field is an affine transfo, we need to compute the space of the concatenate warping field:
        if isLastAffine:
            sct.printv(
                'WARNING: the resulting image could have wrong apparent results. You should use an affine transformation as last transformation...',
                verbose, 'warning')
        else:
            if crop_reference in [1, 2]:
                # Extract only the first ndim of the warping field
                img_warp = Image(warping_field)
                if dim == '2':
                    img_warp_ndim = Image(img_src.data[:, :], hdr=img_warp.hdr)
                elif dim in ['3', '4']:
                    img_warp_ndim = Image(img_src.data[:, :, :],
                                          hdr=img_warp.hdr)
                # Set zero to everything outside the warping field
                cropper = ImageCropper(Image(fname_out))
                cropper.get_bbox_from_ref(img_warp_ndim)
                if crop_reference == 1:
                    img_out = cropper.crop(background=0)
                elif crop_reference == 2:
                    img_out = cropper.crop()
                img_out.save(fname_out)

        sct.display_viewer_syntax([fname_dest, fname_out], verbose=verbose)