I’d like a convenient way to measure the size of an image on a computer screen. My specific intentions are to measure the distance between two points I made on a photo copied electrophoresis gel pattern, where I added the dots via paint. While a physical ruler would be ok, I’ll be doing quite a few measurements, so something more accurate / easier would be better.
The optimal program would be one where I would only need to click between on two points and obtain an immediate measure (in metric) of the distance between the points. I’ve tried the crude method of copying an image on a ruler from google, but when I transfer the image to paint, the size is enlarged dramatically; this makes it hard to measure a metric length, and the resolution of the image gets screwed up badly.
So does anyone know of any free programs that can help me measure distances on a computer screen?
Photoshop, Graphic Converter (free) and any free picture editor CAN do it- I am surprised M.S. Paint can’t. (They almost all have some sort of distance tool which will tell you (difference in X, in Y, and total) which you can use to multiply by your ppi (or ppcm) to get a distance in a measurement). But why? Science has long used Rf, or retardation factor, as the measurement of distance in chromatography.
There are all kinds of problems with the images being autoscaled to your screen or being somehow otherwise manipulated. Going from gel to photocopy (to scan?) to file to measure something is just making it far too complicated and introducing far too much area.
Disheavel has a point. The image might measure differently on your computer and mine because of different screen resolutions, photocoping and other factors. But as long as no ones life hangs in the balance…
Many years ago, I used a program called Screen Calipers which were very handy for doing simple measurements in pixels, which I think would be the only consistent measurement between, say, your computer and mine. You may also want to check out Imal, it was made for scientific image analysis of this nature.
The standard image-measurement tool for the job, for the record, would be ImageJ. It’s kind of clunky but it has lots of tools to measure and analyze gels or micrographs or any biology related image.
Otherwise, if you’ve got a fancy digital imaging station to take pictures of your gels, it probably comes with a proprietary image analysis program that might be easier to use. IME, some of these work pretty well, others are horrifying. That six-figure microscope your department shares probably also comes with some useful software.