There are no images open - Fiji/ImageJ macro language - macros

Question

I wrote a macro in Fiji to perform a set of operations on all the images in a particular folder. But I ran into trouble and can't get over one problem. I get an error message that says 'There are no images open' when I run the macro. What does it mean? (The images in input folder are of .tif type)
Here's the macro:
input = "C:"+File.separator+"Winter Quarter slides"+File.separator+"CTIA"+File.separator+"Project"+File.separator+"Original Image data"+File.separator+"Input Images"+File.separator;
output = "C:"+File.separator+"Winter Quarter slides"+File.separator+"CTIA"+File.separator+"Project"+File.separator+"Original Image data"+File.separator+"Output Images"+File.separator;
setBatchMode(true);
list=getFileList(input);
for(i=0; i<list.length; i++)
action(input,output,list[i]);
setBatchMode(false);
function action(input,output,filename) {
open(input+filename);
run("16-bit");
run("Gaussian Blur...", "sigma=3");
setAutoThreshold("Otsu");
//run("Threshold...");
setAutoThreshold("Otsu");
setOption("BlackBackground", false);
run("Convert to Mask");
run("Close");
run("Watershed");
saveAs("Tiff", output+filename);
close();
}
close();
Can someone please help me out with it asap?
Thanks!

Answer 1

Another thing that would cause this error would be non-image files in the input directory. You loop through all the content in the folder and treat it like an image. If there is for example a text file, the result of open(input+filename) will not be an open image.

Answer 2

When several windows are open, the macro commands need definition of which window to work on.
In my micros i use ; selectWindow("imagename"); before the command. This should hopfully solve the problem.

Answer 3

I've not used the macro language but I have seen that error when developing in Java. Some Plugins require that an image is showing.
If the image isn't showing after open(input+filename); then you need to run a show function to display the image.
You do
run("Close");
run("Watershed");
saveAs("Tiff", output+filename);
So you close the image and then try to do things to the image which would produce that error.