SOLVED Processing pairs of images

[Ian]

I'm trying to write a script which compares pairs of MRI images in a 3rd party image processing app. However, I need to pass it some command-line parameters to generate the output images.

I've got a directory full of files of this format:

T1_00001.jpg and T2_00001.jpg, where the 2nd half number sequence increases by 1 and there are always pairs and always start at 00001.

I'm trying to create a script that reads all of the T1_..... files in the directory, counts them and then repeatedly runs a command line script to generate the images using a series of wildcard numbers.

I start off by counting all those T1 files like this:

Get-ChildItem -filter 'T1_*' -path 'C:\MRIs' | Measure-Object | Select -ExpandProperty Count

That works great and counts all of the files beginning with "T1_" as expected, allowing me to generate the sequence of numbers I need to use.

However, I struggle at the next step (which should be simple!). I need to run a command of this format:

convert T1_00001.jpg T2_00001.jpg -compose minus -composite Result_00001.jpg

I'm trying to figure out a powershell way of running that command the correct number of times, substituting the numeric part with a 5 digit number generated from the count I collected above. This is where I'm currently stuck, so any help with this would be very much appreciated.

 

[Ian]

Here's where I'm at so far, I think I'm almost there as it outputs the correct text - however it just writes it, rather than executing it as expected:

$convertFile = "C:\Program Files\ImageMagick-7.0.7-Q16\convert.exe"
$path = "C:\MRIs";
Set-Location -Path $path;
$fileNumber = Get-ChildItem -filter 'T1_*' -path $path | Measure-Object | Select -ExpandProperty Count;

1..$fileNumber | % { 'invoke-expression -command "convert T1_{0:00000}.jpg T2_{0:00000}.jpg -compose minus -composite Result_{0:00000}.jpg"' -f $_ }

Any ideas as to why it isn't executing the commands? I'm sure I'm doing something silly here!

 

[Ian]

All sorted now . I had some good advice about taking a different route, they suggested a method in which the files are paired and then the suffix is split off. A much more robust way of doing it:

$convertFile = "C:\Program Files\ImageMagick-7.0.7-Q16\convert.exe"
$path = "C:\MRIs";
Set-Location -Path $path;

#Find Tx_something.jpg-files
Get-ChildItem -Filter "T?_*.jpg" |

#Group on ID after _ in filename
Group-Object { $_.BaseName.Split("_")[1] } |
ForEach-Object {
    #Find file in group starting with T1
    $input1 = $_.Group -match '^T1'
    $input2 = $_.Group -match '^T2'
    $output = "$($_.Name).jpg"

    convert $($input1.Name) $($input2.Name) -compose minus -composite $output
}