convert pixel size to mm

[Tuong]

Hi all!

I create an interface with two objects. I measured the range between them in according to y axis ia equal to 100. I think it means that 100 pixels? Is it right?

How can I convert it to mm (millimeter)? Because I want to take the data with real measurement unit.  

Thank you for your advise!

Best regards,

[shoneill]

You need co calibrate your imaging device.

I presume you're working with a camera?

You take a picture of something with known dimensions, find the size in pixels and voilá.

Shane.

[TiTou]

Hi Shane,

voilà, not voilá !

[shoneill]

Oops,

Thanks for the correction.  Voilà it is then.  That's even easier on my keyboard.  Why did I go for the difficult version?

>ahem<.  This was my blatant attempt to be not so left out with all the french-speaking members here.

I shall try to not make the same mistake again, although totally NEW mistakes may be expected

Shane.

[Tuong]

Thank you for your answer!

I just put 3 images on the front panel, without using camera. I let one image run, one was fixed, and one was background. From that, I measured range between two images (except the background). For example, the background have size of 780x450 pixels, the first image was 450x300 pixels, the last one was 700x250 pixels.

How could I convert the range from pixels to mm with them? I try to find the rationale to convert it.

Thanks for you reply so soon. It's so important for me now.

Best regards, 

[shoneill]

I'm sorry,

I simply don't understand what it is you are trying to do.

The answer as far as I can tell remains the same.  The pixels from which the pictures are composed need to be calibrated to real-world distances.

If your pictures are generated (not taken by a camera) then you are asking how large a pixel is on your monitor, no?

Please expand on your application or post some example code or pictures of it (NO BMPs please)

Trying to help,

Shane.

[Tuong]

Thanks.

I'm also sorry. Maybe my explanation made you confuse.

I attached my pictures with having all of images below. Do you see the back of leading car? I would like to measure the range between the dashboard and the leading car.

My pictures have the resolution about 74 dpi.

I hope to be replied from you! Thanks a lot.

Sincere,

[Tuong]

Sorry, I forgot to attach file.

[TCPlomp]

Hi Tuong

you're 74 DPI gives all the information you need, it is a simple unit conversion:

Distance[mm]=distance[pixel]*resolution[DPI]*conversion[inch/mm]

or:
Dist=100*74/25,4=291 mm.

I'm not really sure what you want to do with this info... but i hope you can fish now.

Ton

[Tuong]

Hi!

I also think like that but not sure. Thanks for your help. It helps me a lot.

Regards,