how to convert Pixel to cm or inch (i want to know 1 pixel equal = ?? mm or = ?? cm = ?? inch)

Sir, i want to know 1 pixel equal = ?? mm or = ?? cm = ?? inch

my Pixel Weld Area shown after area calculation is 23842 i getted from weld image region.

How i convert Pixel to cm or inch

There is any equation or formula to convert Pixel to cm or inch

Plz Help me.

[Nishan Dangi]

Calculation of units (Px/Inch/cm/mm)

Pixels (px)

A small square variable units , it depends upon resolution. Resolution: Resolution is a quantity of pixels per inch , we called it DPI (dots per inches) some preset of resolution ; For screen quality; resolution (R)= 72 dpi For printing quality , resolution® = 300 dpi That means : 1 inch = 72 px or 300 px

Inch<> px 1 inch = resolution (R) px 1 px = 1/R inch

cm<> px 1 px = 1/R inch = 1/ R * 2.54 cm ( 1 inch = 2.54 cm) = 2.54/R cm Therefore , 1 cm = R/ 2.54 px

 mm<>px 
 1 px =  2.54 /R cm 
         = 2.54/r   * 10  mm                             ( 1 cm = 10 mm)
         = 25.4 /R mm
 Therefore ,
  1 mm = R / 25.4 px

summary 1 inch = R px 1 cm = R/2.54 px 1 mm = R/ 25.4 px

For resolution 72 dpi, 1 inch = 72 px 1 cm = 72/2.54 px =28.3464567 px 1 mm = 72/ 25.4 px = 2.8346457 px

[Image Analyst]

@Nishan Dangi, that has nothing to do with the resolution in his image. He wants to know how big the weld is in his image, not how big it is on his screen -- that's meaningless. If you just viewed the image on a larger screen, that does not mean the weld in the image is bigger. The weld is the same size regardless of screen size or how many DPI your screen or video adapter has.

Answer 1

[Image Analyst]

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_measure_a_distance_or_area_in_real_world_units_instead_of_in_pixels.3F

I've also attached a demo for you.

[Akhilesh Singh]

That means:

1st i have to measure weld length Manually/Free Hand with help of ruler or tape to get the length and calculate the weld area Manually in mm^2 or cm^2

2nd The pixel which i getted with the help of MatLab : my Pixel of Weld Area shown after area calculation is 23842

Then i do spatial calibration factor this way : {(?? mm^2 )/(23842 pixel)}

calibrationFactor = *{(?? mm^2 )/(23842 pixel)}* ;
distanceInCm = distanceInPixels * calibrationFactor;
areaInSquareCm = areaInPixels * calibrationFactor ^ 2;

It's correct or wrong way to find how to convert Pixel to mm

[Image Analyst]

Well, yes, except that if it's in mm you should use mm in the variable names, not cm. But what length in mm or area in mm^2 did you measure?

[PUAH PEI YEE]

hi sir, the area that we calculate from matlab is in pixel unit or in Sq.pixels?

[Walter Roberson]

That is going to depend upon how you did the calculation of the area.

[Image Analyst]

The area from bwarea() or regionprops() is initially in pixels. We really don't distinguish between linear pixels and square pixels - it's understood from the context. So length and area are both in pixels - you just have to know that to get real world distance you must multiply by the calibration factor, and to get real world areas you must multiply the pixels by the square of the calibration factor. Just think about it and it will eventually make sense to you.

Answer 2

[Waqar Buriro]

Hello , But how can i find the real length of dicom image if that is taken from a online data source. i can not use ruler to measure its mm size? Is there any way.

[Image Analyst]

No. If you don't know the true length of anything in the image, then you can't calibrate. That picture of a moon could be of a poster on your wall, or of the actual moon through a telescope, and they'd both need different spatial calibrations to give the correct distances - either in centimeters or kilometers.

[Akhilesh Singh]

Sir, I agree with you.

[Image Analyst]

Not sure why you accepted Wagar's Question as the best Answer, over mine, it doesn't even answer your question at all.

[Amit Das]

I have this image with spots. I have a vector containing the areas of the spots in sq.pixel. My question is, how can I see the areas in sq.mm just by putting the mouse cursor on the whole?

[Image Analyst]

Amit, you need to use the 'XData', and 'YData' inputs to imshow() and then call impixelinfo().

[Devyani Sankhe]

@Image Analyst can you please write a code to evaluate this distance? I am new user at Matlab