I am building a "batch photo cropper" UI.

I have a list of images to crop, and I can use Manipulate to make a nice cropping UI for each one:

 With[{im = im},
   HighlightImage[im, BoundingRegion@{p1, p2}, ImageSize -> 100],
   {p1, Locator},
   {p2, Locator},
   Button["Crop", Export["foo.jpg", ImageTrim[im, {p1, p2}]]]
  {im, ExampleData /@ ExampleData["TestImage"][[1 ;; 4]]}


Now I would like to add a Crop All button, which would crop and save each image.

But I'm not sure how to pass each inner Manipulate's controls to an outer Button.

Here is a baby example of the behavior I'm looking for:

   Manipulate[a, {a, 0, 1}],
   Manipulate[b, {b, 0, 1}]
 Button["print", Print[a, b]]

The problem is that the print button prints ab, not the numeric values from the inner Manipulates. I would like to "bubble" those out, but I'm not sure how.

Is there a simple way to do this? Thanks!


1 Answer 1


You can use the LocalizeVariables option of Manipulate.

   Manipulate[a, {a, 0, 1}, LocalizeVariables -> False]
   , Manipulate[b, {b, 0, 1}, LocalizeVariables -> False]
 , Button["print", Print[{a, b}]]

If you do not want the variable definitions to spill out of the outer Manipulate then wrap in DynamicModule.

Remove[a, b];
 {a, b}
 , Manipulate[

Your "TestImage" example uses a list instead of individual variables. The TrackingFunction on each of the Manipulate controls can be used to update the list without creating variable for each value.

DynamicModule[{c = Range[.2, .8, .2]}
 , Column[{
   Button["Print", Print[c], ImageSize -> Large]
   , Multicolumn[
       , {
        {a, c[[#]], Subscript["c", #]}, 0, 1
        , TrackingFunction -> {None, Automatic, 
          Function[{v, e}, c[[#]] = v; e = v;, HoldRest]}
       ] & /@ Range[Length@c]

enter image description here

Hope this helps.

  • $\begingroup$ This helps, thank you! One last question: how would you tweak your example to use indexed variables like a[[1]] and a[[2]], instead of a and b, so that I could work with a list? $\endgroup$ Apr 19, 2023 at 13:11
  • $\begingroup$ @ConvexMartian See update. $\endgroup$
    – Edmund
    Apr 20, 2023 at 19:14
  • $\begingroup$ WOW, thank you! I didn't know about TrackingFunction. This is great! $\endgroup$ Apr 21, 2023 at 12:59
  • $\begingroup$ Can I ask why the HoldRest is needed in the "updater" function? It still works without it. $\endgroup$ Apr 21, 2023 at 13:25
  • 1
    $\begingroup$ Ah, without HoldRest, the Messages window complains: Set::setraw: Cannot assign to raw object 0.645. Thank you! $\endgroup$ Apr 21, 2023 at 13:43

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