Converting Image Dimensions from Pixels to Nanometers

Hi all, I am trying to process an image and I am having problems with the dimensions. I know how to get the dimensions of my image, however they are in pixels and I want to convert to nanometers; I don't want to resize the image, just do a conversion. Any tips?

[Matt J]

Is it a 2D image of a 3D scene? If so, object sizes in nanometers will depend on how far the object is from the camera.

[Image Analyst]

@Matt J I'm guessing since the units are nanometers, this is a microscope image so the scene should be fairly flat and all at the same magnification. Or it could be nanoCT but in that case the spatial calibration factor should be constant and stored with the image. It might be stored with the microscope image also (in the header/metadata) or it might have a micron bar burned into the image. Waiting for @Bethany to clarify.

[Bethany]

it is a microscope image yes, taken at 120x magnification. Not sure if that matters, but hopefully that clarifies

[Image Analyst]

It matters. If it were, say a regular camera and a snapshot of your backyard for example, then the magnification would depend on how far each thing was from your camera. So I'm assuming you say my helpful demo below (scroll down this page) and you tried it. Did that answer your question? If not, attach your picture so we can figure out what is going on. And, are you sure that the spatial resolution is not stored in the header of the image?

[Steven Lord]

Do you have something of a known size in the image to compare other objects in the image against? If not, how do you know (using as an example a picture of a train car) whether the picture is a picture of a full-size train car or a picture of a model railroad car? If it's a picture of a model railroad car, how do you distinguish the different scales?

I know your image is not one of a railroad car, but the same types of questions probably apply to your microscope image.

[Bethany]

Maybe I need to clarify more; the objects in my image are supposed to be say around 80nm, however with the psf of the system that may not be recorded accurately. Since I know my magnification, and using the properties of my camera which say the pixel size is 6.5 microns, i was able to calculate the effective pixel size in my image to be 54 nm. When I import my image in matlab, it is 1920 x 1920 pixels, and I just want to convert those dimensions to nanometers for easier calculations later. Sorry if that doesn't make much sense what it is I want the code to do.

[Image Analyst]

You should take a picture of an object of known length, such as a scale or beads of known diameter. Then use my program.

Answer 1

[Image Analyst]

Multiply by a scaling factor determined by measuring the distance of a known object in your image. See my attached demo.