Ask Your Question


Step 0 - A small intro : what can I expect from a Q&A forum?

A Question & Answer forum is basically a forum which is created to help people with their OpenCV implementation problems. This immediately infers that everything posted on this forum should be related and relevant to developing OpenCV applications and problems resulting from doing so.

Keep in mind that this is a forum where we motivate people to go head on with their challenges. Basically the following types of questions are not allowed on this forum:

  1. Questions that handle software that has nothing to do with OpenCV.

  2. Questions about your homework and school projects. Please do not beg for code, instead try some tutorials and tell us what is going wrong. If you have a deadline to catch and the only way is to let people make your projects, then you basically started to late.

  3. Questions that handle general debugging / programming issues. By this we mean problems that should be adressed to the fora specially designed for helping people with these problems out.

  4. Questions about problems with openCV wrappers (EmguCV, JavaCV, OpenCVSharp, ...) or extension libraries (cvBlobsLib, opencvx, ...). Again these problems should be adressed to the proper fora.

Also focus on the fact that the forum is a question and answer area. We do not encourage large discussions inside topics, but still, small remarks can be left using comments. If you want to participate into head on discussions or meet other OpenCV developers, please go to the designated IRC channel ( - #opencv).

Before we start over, a fun fact to know: if you want to assign yourself an avatar, please go to, and register yourself with the same email adress as on this forum. Personalise your account with an image you prefer and it will be visible on this forum.

Step 1 - The forum itself, how to use it?

Before stepping deeper into creating a decent post, we would like to show you the provided functionality on the forum. By knowing how this forum works, we encourage people to participate in its development. Basically the power behind this Q&A forum is that everyone is in fact a moderator. You start out with basic rights, but the more active you become, the more you participate in questions, the more you will be rewarded for it.

This forum uses a reward system, based on karma points, which shows how much other users appreciate your input. For each question you post, for each comment you make, for each solution you provide, people can endorse your efforts. The following steps and illustrations show exactly what is possible.

Karma and badge system

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Karma basically tells you if your contributions to the Q&A forum are useful and helped people to solve their problems. Each vote in favor will generate 10 points, each vote against will subtract 1 of your points. There is a limit of 200 points that can be accumulated for a single question or answer per day.

If one of your questions gets accepted you will gain 15 points.

The table below explains reputation point requirements for each type of moderation task.

- 5 karma points = upvote rights
- 10 karma points = rights to add comments
- 20 karma points = accept own answer to own questions
- 25 karma points = open and close own questions
- 50 karma points = downvote rights & retag questions of other users
- 75 karma points = edit community wiki questions
- 200 karma points = edit any answer & delete any comment

Besides the karma points, the forum assigns badges to people who perform certain moderation tasks. This goes from answering 100 questions to editing enough questions and even adapting or creating tags for questions. This shows to the community which tasks you assign yourself in moderating the Q&A forum.

Voting up/down answers


This functionality is used to express your gratitude to people that help solving your or others problems. Upvoting is done when the question or answer is interesting or satisfying in accordance to the problem. Downvoting is basically used as a warning towards the author of the topic. It is a way of telling them that they should take a second look at their post and try to adapt it, in order to get a good question.

Voting up comments

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For comments, only upvoting is allowed. Since this area is used to have remarks on questions or to make people aware of mistakes, no downvoting is allowed here. It is mainly used to express gratitude versus a good remark or extra insight into the problem.

Accepting answers


Once the problem is solved, the author of the question is allowed to select an answer that helped him the most. This ensures that the question doesn't stay open. If a solution isn't selected after more than 10 days, forum moderators can select an answer instead of the topic owner.

Closing topics or deleting topics

Once you have been around some time and gathered enough karma, it is possible to close down or delete questions. This can be done by pushing the close or delete button in the message options (see figure below).



However, remember to have the courtesy to tell people why you close down their topic by applying the following rules. 1. Give a reason of closure, by selecting the most correct option from the dropdown menu. 2. Add a comment before closing, stating clearly why you have closed the topic down.


Only delete topics or comments if they are completely inapproriate. Examples can be advertising, rude behaviour or pornographic material. For inappropriate behaviour, you could also use the flag offensive button.

Step 2 - Using the information that is already available

Whenever you are in need of help, you should first do some steps to check whether this problem hasn't been solved before. This can be done in multiple ways.

Using the Q&A search button

In the top right corner of the forum, there is a search option. Searching can either be done by topic title or by topic labels. Therefore always try some hits with the search toolbar (as seen in the figure below). It will point you to people having the same issues and many times it will directly lead you to a solution without the need of creating an own topic.


Be aware that topic aren't always marked as answered. However, this does not mean the solution could not be right there. Put some effort in effectively reading through the hits.

If you have a good remark to add to the topic, please do so. Also, if you would find a solution for an unanswered question, put some effort in solving it. You will help the author and the community with your addition.

Using the good old google search engine

People seem to have forgotton that the world wide web actually has powerful search engines that could help you find the solution to your problem. Especially installation problems are solved quite fast this way, without the need of creating a complete new topic.


In order to get a correct hit, try to use some label words specific to your problem accompanied of the words OpenCV, the version, your operating system and the program language used.

Using fora specific for OpenCV

There are many places that contain a lot of solutions to OpenCV problems. Keep always in mind that you are probably not the only one having a certain issue. One of the many used resources, even as answers to problems formulated here, is stackoverflow. The image shows that OpenCV is a common discussed topic there.

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Step 3 - How to formulate a good question? Some important things to keep in mind.

When you finally decide that your question has literally no solution, then your next step is to create a question. Again several steps are included in order to create a good question and to raise the success in getting a decent answer.

First of all open the question interface by pressing the ASK YOUR QUESTION button. A menu will open, enabling you to format your question as preferred.

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When entering the details of your question, please keep the following things in mind.

  • Try to use a good title. The title is used by others to search for their problem. Try to be as descriptive as possible. A title like 'OMFG errors' will not get much response and will definitely get deleted. A title like 'Error in retrieving data from the Hough Transform' will do the opposite and draw people that are interested.
  • Try to focus to your question. Be precise about what your problem is and try to pinpoint the exact problems you want to solve.
  • Please provide the code (if possible) that you are running. It helps people looking into earlier mistakes that could lead to the actual error. However, if you add code, please use the code makeup button.
  • When your question add errors, please add the complete error. It is seriously frustrating to not know what is the complete build output. Add as much debug information as you can collect to make the helping easier.
  • Pay some attention to your language. This is an English forum, therefore make some effort in constructing good sentences. It helps making it more clearly and points out your problem more quickly.
  • Always end with a clear question. Make it bold, make it attractive. This ensures that people know exactly what you are looking for. Even if you elaborated in the beginning, repeat the question at the end of your post.
  • Try to state your operating system (32 bit or 64 bit), the OpenCV version, the options that you used while building. Mention also which programming language you are using. All this information can help forum assistants to quickly search for a specific solution, rather than searching for a general one.

A fairly decent post can be seen below:

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Step 4 - Following up on your question.

When you posted a question, please try to have a frequent follow-up. If you can help by answering peoples questions, your solution can be found fairly faster. Though keep these things in mind at all time:

  • Discussions and remarks go into the comment section.
  • If you have an update, edit your original post and add the extra comments. You can use a horizontal line or a bold text to seperate your remarks from the original post.


Guide created by @StevenPuttemans

Guide checked for spelling errors and buildup by @Guanta