each pixel is identified by its location and each location of the pixel is defined in terms of its count so this is pixel 1 and 1 this is pixel 1 and 2 and so on and this way this is pixel 2 and 1 and this is pixel and then M where m is the number of rows and M is the number of columns and n times M gives you the total number of pixels which basically gives you the number and you can convert it to megapixels and that's the resolution of your sense so that creates
the following opportunity that creates the opportunity to identify any given itself by its location by its coordinates as such so a digital image contains a built-in reference system that runs positive this way and positive this way with a zero and zero will be here off the screen now in such a system can I determine the distance between two pixels and the answer is yes all I have to do is to use they include e'en or the square roots so I have Excel p-one with coordinates let's say x1 y1 both of these are integer numbers and
vixx LP 2 with coordinates x2 and y2 where again these are integer numbers the location of the two cases the distance between p1 and p2 is simply square root of Delta X square plus Delta Y square this is the Euclidean distance in units of pixel plane or pixel size where the pixel size stands for this or this they're the same length so I can measure the length of a line the distance between two pixels by using this simple equation so interesting enough when you take a picture in that picture you can measure length so if
you measure length and since you know that Epsilon strength is Delta L divided by L this will be in units of meter per meter in per inch miles per mile can it be pixel per pixel and the answer is yes you can actually measure strain in units that pixel per pixel it's perfectly fine fundamentally let's do the following let's consider an image sensor I'm going to redraw this let's consider an image sensor divided into pixels as such and let's say that we take a picture of a rubber band let's say that when we take a
picture of their rubber band and I'm going to define here additional pixels let's say that the picture starts in the first picture we take the first picture and the rubber band is gonna cover this pixel and you're going to be recognizing this pixel and this pixel all the way to this place so all in between so the rubber bands the image of the rubber band starts in this pixel and ends in this fix those are the ends of the rubber band now we take a second picture after item distort I change and in the second
picture the rubber band is going to start here and he's going to end up let's say here and he's gonna cover pixels in between so this is the starting point this is the end point where as in the first picture the rubber band starts in this pixel and ends in this pixel can i compute the initial length of a rubber band yes I use that equation between these the chord and the coordinates of these two pixels that's the initial length in units of pixel can i compute from the second image the this length I use
exactly the same equation and the coordinates of this pixel and the coordinates of this pixel the length of the first line of the image of the rubber band in the first picture is gonna give me the initial length the length of the rubber band measured in the second picture is going to give me the final length I simply go ahead and use epsilon is equal to Delta L divided by L final length minus minus initial length divided by H the length and there's your measurement of strength how much normal strain this rubber band undergoes to
digital pictures of the rubber band in its initial configuration and it's in final configuration allow you to measure strain without any other instruments the digital photography technique digital imaging allows you because of its natural coordinate system built into every single picture to actually perform measurements of strength now this is good and this is fine how can they practically make use of this well first of all we actually have to find a way to determine the coordinates of these pixels so when you take a picture of a rubber band in fact you're not going to be
able to tell where which is the pixel where the rubber bat ends because the pixels are so small that you're not meant they are not meant for your eye to be able to tell them apart and that's the case however what you can do is you can use a program like ms paint or photoshop and zoom in and as you zoom in in every single digital image you're going to be able to see the image becoming more more blocky to the point where you can see individual pixels and by zooming in you're gonna be able
to recognize which are the pixels where the rubber band ends now it'll take a little bit of judgment because it's not going to be as clearly defined as in my drawing here but there is a way to actually determine the pixel location make a judgement which is the pixel where the rubber band ends so zooming in to a digital image using a program like ms paint or photoshop is one way to see better to see the pixels individually because normally you don't see them in a 6 megapixel picture the second part has to do is
how do you get these numbers the coordinates at his fix and the answer is that mspaint and photoshop allow you to by just moving your mouse to move the mouse over the specific pixel and it will tell you on the side or on the bottom of the screen the coordinates of that pixel 253 and 5312 those are the coordinates of the pixel so you can actually use in a digital photography you can use the zoom feature and the cursor readout feature to determine to measure the coordinates of a human pixel so that's how you're going
to be able to process an image by hand so what's left here's what's left we're gonna perform an interesting experiment we're going to take pictures with the 24 megapixel camera of a specimen like so it's made out of foam and it has a grid drawn on it there are 1 2 3 4 5 lines that are horizontal and one two three four five lines that are vertical two of which are the edges of the specimen you are creating by so doing the pattern of 25 points 1 2 3 4 5 and so on 25 intersection
points so let me represent that on the stone you're gonna have this pattern this grid that is drawn on this phone specimen that is going to be put in the testing machine a picture will be taken up this grid before deformation then a stretch will be applied using the testing machine and the second digital picture with a
