in reply to Re^3: Use of uninitialized value $pic
in thread Use of uninitialized value $pic

Hello Yes, it wasn't a good night for troubleshooting code. I have incorporated your suggestions and fixed the code.
I used a hash because I have a couple of switches and args that determine which camera is being used and where the files should go.

Moving onto my next problem. I want to call a subroutine ImageNotDark. I want to pass an Image::Magick object ($pic).
By design, the object is not changed inside the subroutine. My problem is that I am not passing the image object correctly. 
# Convert to Image::Maggick image
my $pic = Image::Magick->new(magick=>'jpg');  #   create new image obj
+ect
$pic->BlobToImage($img);  #convert the grabbed blob image to Image::Ma
+gick object

## test point A

#pass the $pic object to the subroutine and measure image darkness.
my $test = ImageNotDark ($pic);  #

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The code snippet at the start of the subroutine is as follows: 
sub ImageNotDark  {
# Argument is one reference to an image object.
# ImageNotDark compares the image with a blank black canvas.  If the c
+omparison is
# above the defined threshold, the image is bright enough to send (not
+ dark).
# the return value is true if the images is bright enough.

    my $iutImage = Image::Magick->new;  #the image tested for darkness
    $iutImage->Read(@_);  # get the image under test (iut)

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So the debugger shows that $iutImage is not initialised. At test point A, I temporarily added code to save the $pic image to a file.
I was able to confirm that $pic holds a valid image. So I am reasonably certain the problem is the way I call the subroutine and attempt to pass the image. Any tips would be much appreciated.

Replies are listed 'Best First'.
Re^5: Use of uninitialized value $pic
by haukex (Archbishop) on Apr 25, 2017 at 06:28 UTC
    Moving onto my next problem.

    As this question is unrelated to the rest of the thread, it'd have been better to post it in a new thread.

    You don't need to construct a new Image::Magick over the argument passed to the subroutine. The normal way to handle arguments is (see perlsub):

    sub ImageNotDark {
  my ($iutImage,$arg2,$arg3,...) = @_;
  # --OR--
  my $iutImage = shift;
  my $arg2 = shift;
  ...

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    Or, if your intention were to work with a copy of the image in the subroutine, you could simply do my $imgCopy = $_[0]->Clone(); inside the subroutine.

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[d/l]
[select]
      Hello
      That is diamond advice.
      My Google search results had not found the perlsub doc and I found conflicting or/and confusing advice around handling objects passed to subs.
      I am sure this will be helpful to others. I will raise this as a separate question and include your answer for the benefit of others who hit the same problem.
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Re^5: Use of uninitialized value $pic
by zentara (Cardinal) on Apr 25, 2017 at 13:51 UTC
    Hi, just a thought. Shouldn't 
     $iutImage->Read(@_);  # get the image under test (iut)

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    be 
    my $x = $iutImage->ReadImage($_[0]);
warn "$x" if "$x";

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    Also, you can try passing \$pic to pass the object by reference.
    I'm not really a human, but I play one on earth. ..... an animated JAPH
[reply]
[d/l]
[select]
      Hi
      I don't know. What does this do: 
      warn "$x" if "$x";

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      Google tells me it's a warning. Undef??

      dazz
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[d/l]

        It's a very ugly hack for error checking. See "Handling Exceptions" in the documentation of Image::Magick. Sane error handling would use die or the XS equivalent of die inside the Image::Magick code, but now it's too late for an incompatible change.

        Alexander

        --
        Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
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