Some options:

Ruler, pencil, calculator and scale it.

Put the image into a 2D CAD programme, Adjust size to 1:1 or a convenient size. Set the graph datum at the CAD drawing datum and lay down a series of points at suitable positions on the graph. Interrogate points for values.

You can do the same in Excel using lines, it is a bit more fiddly but it works well.

Dave

John

Many years ago I used a program called NIH Image to do exactly what you are proposing. Worked well although the control side was primitive by todays standards. Certainly had to read the manual. As I recall it the output was in CSV format which I ported over to CricketGraph to replicate the graph and Excel to do some analysis.

NIH Image was a free to download program developed by the American National Institute of Mental Health for this and many other imaging analysis duties. Ran under the Classic Macintosh OS. Now long obsolete, although it seems still to be available for download, it has been replaced by ImageJ which runs on Java.

ImageJ in a much more sophisticated program but I presume has the same capabilities buried inside it.

ImageJ is also a free download.

Allegedly there are ways of running NIH Image on a PC or modern MacOS but locating the port or emulators may be a problem.

Clive

PS Quote from https://imagej.nih.gov/ij/docs/intro.html about what ImageJ can do.

"It can display, edit, analyze, process, save and print 8-bit, 16-bit and 32-bit images. It can read many image formats including TIFF, GIF, JPEG, BMP, DICOM, FITS and "raw". It supports "stacks", a series of images that share a single window. It is multithreaded, so time-consuming operations such as image file reading can be performed in parallel with other operations.

It can calculate area and pixel value statistics of user-defined selections. It can measure distances and angles. It can create density histograms and line profile plots. It supports standard image processing functions such as contrast manipulation, sharpening, smoothing, edge detection and median filtering.

It does geometric transformations such as scaling, rotation and flips. Image can be zoomed up to 32:1 and down to 1:32. All analysis and processing functions are available at any magnification factor. The program supports any number of windows (images) simultaneously, limited only by available memory.

Spatial calibration is available to provide real world dimensional measurements in units such as millimeters. Density or gray scale calibration is also available."

Edited By Clive Foster on 05/05/2021 11:45:21

That could almost have been bespoke for your job !!

… duly noted for future reference.

MichaelG.