Daheng image : Founded on 1991 year , Focus on Visual components 、 Vision system and Internet medicine Related product development 、 High tech enterprises for production and marketing .

Product information :

1. Image capture card

The analog image signal input by the camera passes through A/D transformation , Or the output signal of the digital camera , By computer Bus To the computer Memory or video memory , The computer can process and store the collected images in real time .

2. Digital cameras

1) sensor : The core of the camera ( Camera commonly used photosensitive chip :CCD、CMOS)

  • CCD( Charge coupled devices ) Three structures : Full frame transfer 、 Frame transmission 、 Line transfer

  • CMOS( Complementary metal oxide semiconductor ): Except for the sensitive part , There are also amplifiers and readout circuits , Whole CMOS The sensor is also integrated with an addressing circuit 、 Amplifiers and A/D.

2) Image acquisition mode

Image acquisition mainly refers to : When to start collecting ?、 The length of the exposure ?、 How to end the collection ?

  • The beginning of the acquisition usually has Software acquisition and external hardware signal trigger Collect two kinds of data . Software acquisition is that the computer sends the acquisition command to the camera , It can be single frame acquisition or multi frame continuous acquisition ; External trigger acquisition starts acquisition through external trigger signal , The signal can be triggered by rising or falling edge or level .
  • time of exposure , Software command acquisition is to achieve different length of exposure by programming registers ; The edge trigger mode of external trigger acquisition is also realized by register programming , The level trigger is controlled by the duration of the triggered level .
  • The end of acquisition control is mainly aimed at Software acquisition , Automatically clear acquisition command after single frame acquisition , The continuous acquisition needs the computer to issue the command to clear the set acquisition command .

3) Data output mode

USB、1394a、1394b、Camera Link and GigE

4) How to choose the right digital camera

  • The minimum feature and detection field of view are defined , The resolution of the camera is thus determined
  • According to the speed and passing rate of the target , Determine the frame rate of the camera ( Line frequency )

3. The light source

(1) The properties of the light source itself , Such as the spectral distribution of the light source , The brightness distribution on the illuminated surface , Temperature characteristics and life of light source in use .

(2) The interaction between the light source and the illuminated object . A light source shines on an object , There's a reflex 、 There are three kinds of interaction between absorption and transmission , Objects of different materials , The three effects produce different phenomena , Defective parts and other parts of the same object , The three effects produce different phenomena . For example, in surface inspection , We can roughly divide the defects in the target into two categories :

  • One is geometric defects , Such as : A pit 、 Scratches 、 Crackle 、 skin needling 、 Bulge 、 Bruises 、 Bruises, etc
  • The other is surface strength ( Or density ) defects , Such as : oxidation 、 Rust 、 The stain 、 Stains, etc

The former makes the surface Reflection change , The latter makes Surface reflection and absorption Everything has changed . Only by carefully studying the characteristics of the interaction between the light source and the object , In order to determine the light source and lighting mode . The color of an object is another example of light absorption . Full band white light hits the surface , Some wavelengths of light are absorbed by the surface of the object , Some wavelengths of light are reflected by the surface , Objects show the same color spectrum as reflected light . Take advantage of this , We can use black and white cameras , Choose a light source with a specific wavelength , Highlight the gray difference between the part to be detected and other parts of the object surface , To achieve reliable 、 Stable detection .

(3) The structure of the light source . Light sources can be made into various shapes and structures , Each shape emits different characteristics of light . Such as : Diffuse light , Uniform illumination can be obtained on the target plane ; Direct light , Show edges and surface structures by reflection and shadow generation , But the movement and tilt of the light source or target will obviously affect the brightness and contrast of the image . in addition , The light source can be placed above or below the illuminated object , There can be various angles and heights , Through the combination of different shapes and lighting methods , Using things like creating shadows 、 The method of producing highlight area or no reflection area , Make the region of interest on the target as different as possible from other regions .

Design the light source system , The ultimate goal is : Maximize the contrast of the features of interest , Restrain and reduce the influence of other parts of the target , Restrain the influence of external environment .

Self introduction.

1. Brief introduction of education background and major :

2. Work / Project experience ( a key ):

  • Summarize the main responsible points and achievements in the work
  • To explain it in an organized way , But it has to be related to the position .

3. Self evaluation :

  • advantage : Compressive ability 、 Self study ability 、 Ability to solve problems ( put questions to - analysis - Search for - extract - restructure - Internalize - verify - to update )
  • shortcoming : have grandiose aims but puny abilities 、 Execution needs to be strengthened
  • Be a man and do things : A person ——3 Ways of planting ; To do things : Preview and replay .
  • Thinking about life : Do as you please , The importance of thinking .

skill :

1. Time control

Self introduction is best controlled in 2-3 minute . It's like watching TV commercials , Design your self introduction as an advertisement , It is necessary to arouse the viewers' desire to buy in limited time .

2. Content control

Pay attention to introduce what you are good at. It must be closely related to the position you are applying for , Mainly around professional expertise to introduce . In addition to professional expertise , If it is particularly prominent, we can introduce , But the point is so far .

3. There is a clear professional logic

There are three periods of career : Study period 、 Growing period 、 mature period . Workplace learning and growth , Brief introduction , But don't omit , Because the study period marks the way you do things , Growth represents the way of professional improvement and management improvement . Focus on maturity , Can things be done at maturity , What has been done , Under what circumstances , Both represent the wisdom and career maturity of a person in the workplace . There should be a clear logical relationship between these three periods of career change . Self introduction. - Interview questions now - future - The past includes work patterns 、 advantage 、 Skill , Outstanding achievements 、 Professional knowledge 、 Academic background, etc . But one thing to remember : Where the topic goes , You have to highlight your contribution to the company , Such as increasing turnover 、 Reduce costs 、 Explore new markets, etc .

4. The control of expression

No matter how wonderful the content is , Without beautiful packaging , It still doesn't work . So in the self introduction , You have to pay attention to your performance in all aspects , Especially the sound line . Don't introduce yourself by reciting . You'd better find some friends to practice with in advance , Try to make the voice sound smooth and natural , Be confident . Body language is also an important part , Especially eye contact . It's not just about keeping the audience focused , You can also show confidence . There was a report that , Daily communication , Nonverbal accounts for 70%. therefore , If you want to succeed in the interview , You should remember to pay attention to your body language .

Q&A

One 、C++

1. Talk to you about static|const The understanding of the ?

  • const It means read-only , Only in Statement Use in ;
  • static Generally speaking, there are 2 A role , Regulations Scope and storage . For local variables ,static It is defined as static storage , The initial value of each call is the value of the previous call , The storage space is not released after the call ; For global variables , If the scope is divided by file , This variable is only visible in the current file ; about static Functions are also visible in the current module .

2. How do you understand inheritance 、 Polymorphism and combination ? Please give an example of their application .

  • Inherit : It can use all the functionality of an existing class , And extend these functions without having to rewrite the original class . The process of its inheritance , It's a process from general to special .———— code reuse
  • polymorphic : polymorphism (polymorphisn) Is a technique that allows you to set a parent object equal to one or more of its children , After the assignment , The parent object can then behave differently depending on the properties of the child object currently assigned to it . To put it simply , In a word : Allows assigning a pointer of a subclass type to a pointer of a parent type .————— Interface reuse
  • Combine : Describe the relationship between the whole and the parts , One object is part of another .

3. How do you understand heaps and stacks ? Please state in which cases , The object instance is in the heap or stack ?

  • The stack area (stack)— Release is automatically allocated by the compiler , Stores the parameter values of the function , The value of a local variable, etc . It operates like a stack in a data structure .

  • Heap area (heap) — Release is usually assigned by the programmer , If programmers don't release , At the end of the program, the OS Recycling . Notice that it's not the same as the heap in the data structure , The distribution method is similar to the linked list .

4. How do you understand processes and threads ? How to realize synchronization between threads and communication between processes ?

  • The user space of processes is independent of each other , Generally, they can't visit each other , Interprocess communication is about how to transfer information between two programs .—— Distribution
  • Multiple threads in the same process can share space resources , There is a problem of synchronization between multiple threads .

5. How to understand MFC Message mechanism ? Talk about right DLL and COM The understanding of the .

  • Depending on the source ,1. Mouse and keyboard system internal control messages and other native messages , Is captured by the operating system , Then it is sent to the message queue of the current thread for processing , After thread function translation , And then execute the corresponding function , Or redistribute it to the window .2. adopt SendMessage,SendThreadMessage And so on , Directly into the thread's message queue , Then process ,3 adopt SendMessage Messages sent to the window , Call the window's message handling function directly , Without threads .

  • In multiple inheritance dll Can't satisfy the problem of the same name , and com Yes. ; from The essence Say above ,COM Follow DLL There's no difference , It provides a series of interfaces (Interface) For developers , And only one copy is kept in memory when it is called . The difference is ,COM Our organizational structure is similar to DLL It's different .COM Trying to provide developers with a clear library structure . We know ,DLL It's just a combination of functions , Go further , If we export DLL Is a class , So it's a class structure . This hierarchy is fuzzy .COM Every exported class must inherit an interface class . in other words , We are going to export a class with certain functions ( For example, arithmetic Math), We have to define its interface (InterfaceOfMath).

Two 、Linux

1. describe linux Boot to login interface The boot process

  • Turn it on BIOS Self inspection
  • MBR guide
  • grub Guidance menu
  • Loading kernel kernel
  • start-up init process
  • Read inittab file , perform rc.sysinit,rc Etc script * start-up mingetty, Enter the system login interface
  • describe linux The difference between soft link and hard link .

2.linux shell In single and double quotation marks or without quotation marks difference

3.linux Operation level 0-6

  • 0 For shutdown , Machine off .
  • 1 For single user mode , It's like Win9x The security mode under is similar to .
  • 2 For multi-user mode , But no NFS Support .
  • 3 For the complete multi-user mode , Standard operation level .
  • 4 Generally do not use , In some special cases, you can use it to do something . For example, when the battery of a laptop is exhausted , You can switch to this mode to make some settings .
  • 5 Namely X11, Enter X Window The system .
  • 6 For restart , function init 6 The machine will restart .

4. describe linux Next File deletion Principle

Linux It's through link To control the number of deleted files , Only when a file does not exist any link When , This file will be deleted .

5. describe linux The difference between soft link and hard link

  • Soft links overcome the shortcomings of hard links , There are no file system restrictions , Any user can create symbolic links to directories .
  • Hard link is a pointer , Point to the file index node , The system doesn't reallocate it inode

3、 ... and 、 Theoretical basis and algorithm knowledge of image processing and machine vision

1. Which parts does a machine vision system consist of ? Try to discuss it in detail .

  • Image acquisition : It is to transform the visual image and internal characteristics of the detected object into a series of data that can be processed by the computer . This part mainly includes , lighting 、 Image focusing optical system 、 Image sensors ( Mainly CCD and CMOS) Collect object images .
  • Image processing and recognition : The processing of visual information mainly includes filtering and denoising 、 Image enhancement 、 smooth 、 Edge sharpening 、 Division 、 Image recognition and understanding . After image processing , The quality of the image is improved , It not only improves the visual effect of the image, but also facilitates the computer to analyze the image 、 Process and identify .
  • Output display and control : It mainly outputs the analysis results to the display or control mechanism and other output devices

2. What are the main forms of image gray transformation ? What are their respective characteristics and functions ?

  • Global linear transformation , In the case of underexposure or overexposure , The grayscale of the image may be limited to a very small range . What you see on the monitor is a blur 、 There seems to be no gray level image . Using a linear single valued function , Each pixel within the frame is expanded linearly , Will effectively improve the visual effect of the image .
  • Piecewise linear transformation : Divide the gray range into two or more segments and do linear transformation respectively . The advantage of piecewise linear transformation is that it can be used according to the needs of users , Stretch the grayscale details of feature objects , Relative suppression of gray levels of interest .
  • Nonlinear transformation : It can realize the nonlinear transformation of image gray level , for example , Logarithmic transformation , When you want to expand the low gray area of the image and compress the high gray area , You can use this transformation . It can make the gray distribution of the image even , Match the visual characteristics of people .

3. What are the principles of image feature extraction ?

  • reliability , The characteristic values of the same kind of images are close to each other ;
  • Different sexes : The feature extraction of different types of images should have obvious differences ;
  • independence : Each characteristic quantity should not be related to each other ;
  • Simplicity : It should have less characteristic quantity .

4. This paper discusses the basic concepts of image recognition . What are the common discriminant functions ?

  • It refers to the quantitative description of various object features in the image , Extract the desired object , And quantitative analysis of the extracted target .
  • Image recognition is an important field of artificial intelligence . Use the computer to process the image 、 Analysis and understanding , Technology to identify targets and objects of various patterns . Common discriminant functions are : Linear discriminant function 、 The minimum distance discriminant function 、 Recent domain discriminant functions 、 Nonlinear discriminant function .

5. Overview of moving object detection

6. Overview of visual tracking

Four 、OpenCV

1.CV

Image processing and vision algorithm

2.HighGUI

GUI, Image and video I/O

3.CXCORE

basic structures and algorithms, XML support, drawing functions.

The Truth

One 、 A simple self introduction

About the subject 、 About what's on your resume 、 Projects related to machine vision

Two 、 written examination

1. ordinary C、C++ Read the program

2. Two questions :

  • sendmessage and postmessage difference
  • MFC In the module dialog box and non module dialog box

3. A translation about the application of machine vision

reference :

1. How to introduce yourself in an interview

2. Han Wang machine vision software engineer interview questions

3.C++ encapsulation 、 Inherit 、 polymorphic

4.C++ Complete parsing of heap and stack in

5.C/C++ Stack guidance

6. Ruan Yifeng's Weblog A simple explanation of process and thread

7. Interprocess communication mode , Synchronization between threads

8.Linux The difference and connection between hard link and soft link

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