How to know how many pixels are a millimeter in my image?

I got some dimensions in pixels from the image below (for example TotalArea=520000 pixels). I need to convert my dimensions from pixel to millimeters. I'm a newbie in matlab and I don't know where to start with this. I've already made the calibration with the Camera Calibrator provided by Matlab and I've obtained two folders:

• CameraParameters
• EstimationError

The image is the following:

Answer 1

[Matt J]

You need to know the length in millimeters of a particular object or feature in the image to make that conversion.

[mirko]

I know the lenght of the chip's side (36 mm)

[Matt J]

Well, the image gives that length to you in pixels as well, so you can calculate the mm per pixel.

[mirko]

That's right but how can I convert my Area from pixel to millimeters with Matlab so I can compare the measure in mm computed by Matlab and the real measure that I got in real life ?

[Matt J]

Once you have the pixel/per millimeter conversion factor, any measurement in pixels can be converted to millimeters, can't it?

Area=Area*mm_per_pixel^2

[DGM]

Might want to be a bit careful with calibrating off the substrate edges, given their indistinctness due to the shadows. It might be better to calibrate off the grid array if it can consistently provide better contrast. Just a thought.

[Image Analyst]

@DGM right. I mentioned shadows and background flattening to him in his other question but he just said I was criticizing his question and he didn't want any more help from me. Too bad. With my 45 years experience designing imaging systems and image analysis software I could have been helpful.

[mirko]

I can't get a better image than this due to limited instrumentation. In the last hours I partially solved my problem. I got from Matlab a length of 34 mm for the external side of the CPU when the real length is 36 mm. I can accept this error. The problem is when I try to get the pins' diameter: Matlab give me a value of 16 mm but it is impossible because the real diameter is 0.9 mm. If you can help me, I can send the code I'm trying