print ROI coordinates in 2D image plots using the Marquee tool as input device

Here's a snippet to print the coordinates of a region of interest in a 2D image plot that was selected by the Marquee tool. Paste the code to the procedure window, compile, and use it on your image by drawing a Marquee box with the mouse, then right-click (Windows) or cmd-click (MacOS) to get the Marquee context menu, and choose "Print Image ROI". The snippet should work no matter which axes you use (top or bottom). You should have only one image on the plot, but this behavior can be changed easily, see comments in the code.

Menu "GraphMarquee"
    "Print Image ROI"
End

Function PrintImageROI()
// 1. get the marquee in point units (axis units directly accessible only for 1D graphs!)
// sanity test: let there be exactly one image
    String TopGraphImages = ImageNameList("",";")
    if( ItemsInList(TopGraphImages) != 1 )
        Print "There is either no image or more than one on the graph"
        return -1
    endif
    GetMarquee
// sanity test: was there a marquee at all?
    if (V_flag == 0)
        Print "There is no marquee"
        return -1
    endif
    Variable mpL = V_left, mpR = V_right, mpT = V_top, mpB = V_bottom
//  print "marquee in points (left, top, right, bottom) =", mpL, mpT, mpR, mpB

// 2. get the plot area in point units
    GetWindow kwTopWin, psize
    Variable ppL = V_left, ppR = V_right, ppT = V_top, ppB = V_bottom
//  print "plot area in points (left, top, right, bottom) =", ppL, ppT, ppR, ppB

// 3. get the axis limits
// get limits of axes that image is displayed against
    String theImage = StringFromList(0, TopGraphImages)
    String XAxis = StringByKey( "XAXIS", ImageInfo("", theImage, 0) )
    String YAxis = StringByKey( "YAXIS", ImageInfo("", theImage, 0) )
    String XAxisLimits = StringFromList(2, StringByKey( "SETAXISCMD", axisinfo("", XAxis) ), " " )
    String YAxisLimits = StringFromList(2, StringByKey( "SETAXISCMD", axisinfo("", YAxis) ), " " )
// order left/right correctly, remember whether a swap occurred
    Variable axMin = str2num( StringFromList(0, XAxisLimits, ",") ), axMax = str2num( StringFromList(1, XAxisLimits, ",") )
    Variable paL = min(axMin, axMax), paR = max(axMin, axMax), xSwap = (paL != axMin)
// order top/bottom correctly, remember whether a swap occurred
    axMin = str2num( StringFromList(0, YAxisLimits, ",") ); axMax = str2num( StringFromList(1, YAxisLimits, ",") )
    Variable paT = max(axMin, axMax), paB = min(axMin, axMax), ySwap = (paB != axMin)
//  print "plot area in axis units (left, top, right, bottom) =", paL, paT, paR, paB; print xSwap, ySwap

// 4. express the marquee coordinates in axis units
    Variable maL = paL + (mpL - ppL) * (paR - paL)/(ppR - ppL), maR = paL + (mpR - ppL) * (paR - paL)/(ppR - ppL), swap
    if( xSwap )
        swap = maL; maL = maR; maR = swap
    endif
    Variable maT = paT + (mpT - ppT) * (paB - paT)/(ppB - ppT), maB = paT + (mpB - ppT) * (paB - paT)/(ppB - ppT)
    if( ySwap )
        swap = maT; maT = maB; maB = swap
    endif
    print "marquee in axis units (left, top, right, bottom) =", maL, maT, maR, maB
End
Hi Harneit,

Thanks a lot for writing this, it was just what I was looking for. I do have a slight amendment to make though. Where you get the axis limits from the "SETAXISCMD", if the image axes are set to auto the returned string i.e. XAxisLimits is "" and the returned marquee values are NaN. I have made the following changes to avoid this:

    String XAxisLimits = StringFromList(2, StringByKey( "SETAXISCMD", axisinfo("", XAxis) ), " " )
    String YAxisLimits = StringFromList(2, StringByKey( "SETAXISCMD", axisinfo("", YAxis) ), " " )
   
// order left/right correctly, remember whether a swap occurred
    Variable axMin, axMax
    if ( strlen(XAxisLimits) == 0 )     // i.e. SetAxis/A bottom
        axMin = DimOffset($theImage,0) - ( DimDelta($theImage,0) / 2 )
        axMax = axMin + DimDelta($theImage,0)*DimSize($theImage,0)
    else
        axMin = str2num( StringFromList(0, XAxisLimits, ",") )
        axMax = str2num( StringFromList(1, XAxisLimits, ",") )
    endif
    Variable paL = min(axMin, axMax), paR = max(axMin, axMax), xSwap = (paL != axMin)
   
// order top/bottom correctly, remember whether a swap occurred
    if ( strlen(YAxisLimits) == 0 )     // i.e. SetAxis/A left
        axMin = DimOffset($theImage,1) - ( DimDelta($theImage,1) / 2 )
        axMax = axMin + DimDelta($theImage,1)*DimSize($theImage,1)
    else
        axMin = str2num( StringFromList(0, YAxisLimits, ",") )
        axMax = str2num( StringFromList(1, YAxisLimits, ",") )
    endif
    Variable paT = max(axMin, axMax), paB = min(axMin, axMax), ySwap = (paB != axMin)
   
//  print "plot area in axis units (left, top, right, bottom) =", paL, paT, paR, paB; print xSwap, ySwap


Cheers!

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