I have an image of a chart showing Young’s modulus of iron plotted against temperature. There are several sets of data from different studies shown on the chart as curves and I would like to be able to overlay onto this a line that is a reasonable fit amongst these curves.
I tried to do this by generating a chart in Calc and setting the background to 100% transparent. I hoped that when I exported this to a .png file the transparency would remain so that I could overlay this chart on the image and the image would still be visible beneath the chart, but the exported .png chart has an opaque white background.
Any suggestions as to how I can use Calc to plot a line on an existing image of a chart would be welcomed.