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Measuring size of objects in an image with OpenCV
The project provides a script to read an image and based on the dimensions of a reference object find the dimensions of other objects in a scene. The reference object must be the leftmost object in the scene. In sample images given, a box of dimension 2cm x 2cm is taken as a reference object. For any other reference object provide actual width of the object. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
Sign up. Measure size of an object height and width using a reference object. Python Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again.
Latest commit. Latest commit 6dcfe03 Mar 11, Measure size of objects in an image using OpenCV The project provides a script to read an image and based on the dimensions of a reference object find the dimensions of other objects in a scene.
It only takes a minute to sign up. How to calculate the real size of an object from two photos in different types of perspective, knowing the dimensions of one of the objects in these pictures?
When I was in college, we did such calculations but it was a long time ago and I have no records. From what I remember,We need the coordinates of a known object from both photographs and the coordinates of the object searched from both photographs. And the realdimensions of the known object. There are quite a few methods to determine this. The most common that you probably noticed would be in crime scene photos when an object of known size such as a pencil or even better a ruler is placed next to the object of interests.
From this it is very easy to estimage the size of the object of interest. As long as you know the focal length and the object distance, both of which some lenses return to the camera you can calculate the real size of an item in the image.
The focal length will give you the lens field of view in terms of degrees. Measuring size of objects in an image with OpenCV. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How to calculate the real size of an object from two photos in different types of perspective, knowing the dimensions of one of the objects?
Ask Question. Asked 2 years, 2 months ago. Active 2 years, 2 months ago. Viewed 12k times. Is anyone able to give a formula how to calculate it? Mateusz Marzetz Mateusz Marzetz 31 1 1 gold badge 1 1 silver badge 2 2 bronze badges. Active Oldest Votes. Measuring size of objects in an image with OpenCV Parallax I'd try looking at these to start off You also might find these of use: visualsize techcrunch on visualsize.
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Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Photo of the Week. Imperfectly Beautiful: Razor Wire by rackandboneman.This is a convenient online ruler that could be calibrated to actual sizemeasurements in cm, mm and inch, the upper half is the millimeter ruler and centimeter ruler, the lower half is an inch ruler. In order to accurately measure the length of your item, we strongly recommend that you calibrate this online ruler first, set the correct pixels per inch to your own device, after adjustment, you will have the most precise ruler online.
Save the pixels per inch PPI according your own device, then you can use this ruler next time. Pixels per inch :show ruler adjuster. Dragging ruler adjuster left or right to fit the size of your reference object, remember to save the setting for the next time you use it, after save the setting, refresh your brower to check the result.
On the most popular browsers you can press the F5 key or click on the refresh button. We hope to provide a more user-friendly experience, are you willing to offer a native language version for your country? We are looking for volunteer to improve the content in your native language, if you are interested to help this, please visit this translation page. Below are some other language version.
One day, i took my laptop computer to work in the coffee shop, just had a project on hand, and i had to tell the customer the actual size of a product. Just like usual, i didn't carry a ruler with me, so i connected to the internet and tried to find an online virtual ruler to measure my product. Unfortunately, after i tried the virtual online rulers on the Internet, i found a problem that these existing online rules are not very accurate.
If i just want to know what the approximate length is, that's fine, but what i need is a more precise length so that i can apply it to my daily work. So later, we developed an online ruler by ourselves. It not only improves the accuracy of the measurement, but also has a scale of inches and centimeters so that it can be used in our work. If you are like us, you need a precise online ruler to measure the product size, i believe this online virtual ruler can also meet your needs.
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This ruler measure in two different units of length, inches on one side English ruler and centimeters on the other side metric ruler. A metric ruler is use to measure centimeter cm and millimeter mmthe centimeter is a unit of length in the International System of Units; An English ruler provides incremental measurements in inches, with each inch further divided into smaller fractions.
Read an English ruler using fractions of an inch. The distance between any two large numbered lines is 1 inch. Observe the much simpler metric rulers. The distance between any two large numbered lines is 1 cm, a metric ruler features two types of lines.
The largest mark centimeters, or cm. The smallest lines mark millimeters, or mm.
I've already found, in general, it's called photogrammetry and seems active research field. How would you find the height of objects given an image? Due to your assumption The reference and target are on the approximately same plane. Antonio Criminisi. In: Pattern Recognition. Lecture Notes in Computer Science. Springer Berlin Heidelberg,pp. The unit of measures of p are pixels, so for example if p is a point at row r and column c it will be expressed as [r,c,1].
Given an image of a planar surface estimate the image-to-world homography matrix H. Assume that the 9 elements of H are dimensionless.
Back-project each image point into the world plane via 1 to obtain the two world points P1 and P2. You do the matrix-vector multiplication and then you divide the resulting vector for its third component in order to get an homogeneous vector.
Assume for the moment that the nine elements of H are dimensionless, that means that the unit of measure of X1Y1X2Y2 is pixel. Now, since P1 and P2 are on the reference object it means that you know the distance between them in meters, let's call that distance, expressed in meters, M. Multiply each element of H by s and call G the new matrix you get. Now the elements of G are expressed in meter per pixel.
Now, in the image select two points p3 and p4 belonging to the target object. Back-project p3 and p4 via G in order to get P3 and P4. Again divide each vectors by its third element. D is now expressed in meters. The appendix of the above mentioned paper explains how to compute H or for example you can use OpenCV cv::findHomography : basically you need at least four correspondences between points in the real world and points in your image.
Metric measurements on a plane from a single image. TR Distinguished Dissertation Series. Springer-Verlag London Ltd. ISBN: Input image, in this case your reference object is the A4 sheet and the target object is the slide rule:. Input image with measures, the red crosses are used to estimate the homography:. The rectified image:. Then multiply the pixel dimensions of the object you want to measure with that factor. This only works if both objects are within the same plane parallel to your sensor.
For anything else you require distance information. You can either measure them or make some asumptions depending on how accurate you have to be.This is a transparent on-line protractor, also helps you measure angles in a picture, you can easily measure the angle of any object around you, taking a picture and uploading it, then dragging the midpoint of the protractor to the vertex of the angle.
Every time I want to measure the angle, I always can't find the protractor. Fortunately, here is an online protractor that is convenient and practical.
Now, we can use laptops, computers, tablets or smart phones to measure the angle of anything, around us anytime, anywhere. If you want to measure something that is small, just place it on the screen and measure it directly; If you want to measure something bigger, you can take a picture and upload it, then move the center point of the protractor to measure its angle. You can take picture of any object that you would like to measure, for example, a car, road, house, stairs or a mountain, the protractor is transparent, after you uploaded the image, it will be display in the background.
In the control panel, if the background color is close to the protractor, and it's not easy to distinguish, you can change a protractor color to see it clearly. Also you can move it, shrink or enlarge the size of protractor, according to your needs.
Disclaimer: Use of the protractor within this website is free. Whilst every effort has been made to ensure the accuracy of the protractor published within this website, you choose to use them and rely on any results at your own risk. We will not under any circumstances accept responsibility or liability for any losses that may arise from a decision that you may make as aresult of using this protractor.
Similarly, we will not be requesting a share of any profits you may make as a result of using the protractor. Online Protractor. Background image :. Reverse Image Search Custom Wristbands.Documentation Help Center.
The Distance tool allows you to measure distance with a click-and-drag approach. When you move the pointer over the image, the pointer changes to cross hairs. Position the cross hairs at the beginning of the region you want to measure, hold down the mouse button, drag the cross hairs to the end of the region, and release the button.
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The Distance tool displays the Euclidean distance between the two endpoints of the line in a label superimposed over the line.
The tool specifies the distance in data units determined by the XData and YData properties, which is pixels, by default.
An alternative to using the Distance tool in Image Viewer is to open a figure window using imshow and then call imdistline. The Distance tool appears as a horizontal line displayed over the image. You can reposition the line or grab either of its endpoints to resize the tool.
To save the endpoint locations and distance information, right-click the Distance tool and choose the Export to Workspace option from the context menu. The Distance tool opens the Export to Workspace dialog box. You can use this dialog box to specify the names of the variables used to store this information. After you click OKthe Distance tool creates the variables in the workspace, as in the following example.
Using the Distance tool context menu, you can customize many aspects of the Distance tool appearance and behavior.How to Measure object size in Adobe Illustrator
Position the pointer over the line and right-click to access these context menu options. Toggling the distance tool label on and off using the Show Distance Label option. Changing the color used to display the Distance tool line using the Set color option. Constraining movement of the tool to either horizontal or vertical using the Constrain drag option. Deleting the distance tool object using the Delete option.
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Select a Web Site Choose a web site to get translated content where available and see local events and offers. Select web site.Calculate Distance or Size of an Object in a photo image This is rather specialized, but people do ask how to determine or measure the distance or size of an object or subject in a photo image.
It is simple math, but it will require knowing accurate focal length and sensor sizes of your camera, which are all important to calculations, but which can be difficult to obtain for automatic cameras, especially cell phones.
And if using an option requiring focus distance, you really ought to first verify the accuracy of what focus distance is reported by your lens at that actual distance and zoom value. A camera is really not a precision measuring instrument.
A warning seems justified: Acquiring the necessary accurate input data likely may be difficult. It will tell you all I could repeat in email.
If your results don't seem reasonable, distrust and verify all of your inputs including sensor size, focal length, aspect ratio, and scene distance dimension. Only specify the real focal length of your actual cameras lens. The real focal length of the normal lens of a phone camera is in the general neighborhood of about 4 mm.
The reported Focus Distance in the image Exif is Often NOT very accurate try verifying it at your same zoom focal length and focus distance. For evidence to make this point, see this chart about measured distances vs what some high end lenses reported for focus distance. That article is about balanced flash problems trying to use the lens distance to control TTL direct flash exposure, but that lens chart applies here too for the same reason.
If using the reported distance, it needs to be measured and verified at the same zoom and focus distance you will be using. The lens distance possibly might be about correct sometimes, but that sure seems Not the way to bet. Zoom lenses and internal focusing lenses are the worst about reporting accurate focus distance. There are plenty of issues when trying to determine the sensor size of compact or phone cameras.
Also with mixed formats both video and still photo images from the same camera. For the various calculators here, these Issues of determining camera sensor size are summarized on one place. Please see that if any issues with sensor size. It can compute your accurate sensor size, and it may be the only manufacturers specification you can ever find for compacts and phones.
Equivalent focal length is the focal length used on another cameraspecifically a hypothetical 35 mm film camera which is of known size and is the standard reference of comparisonwhich will produce equivalent Field of View size on THAT 35 mm film camera.
The Field of View is what is equivalent on the two cameras. Some web sites repeating phone specifications show an Equivalent focal length number instead of the real actual focal length the phone actually uses.
But that Equivalent focal length is Not even about your camera, it is simply a comparison to another lens that is instead used on another hypothetical 35 mm film camera for it to then see the same Field of View that your camera sees. A normal cell phone focal length is typically somewhere around 4 mm, and is NOT any 26 or 28 mm number you might see online somewhere.
Beginners apparently hear the Equivalent term and often get the very wrong idea that their lens somehow magically changes to be the Equivalent focal length, but that is impossible, it cannot magically change.