How to Choose the Best 4K Camera for Your Application

I need 4K resolution USB camera, what would you recommend me?

This is a common question that I am asked by customers, unfortunately the answer is not simple.

First, a quick review on the criteria to be a 4K camera. The term “4K” comes from TV terminology and is derived from full HD resolution.

Full HD is 1920 x 1080 = 2,073,600 total pixels
4K is 3840 x 2160 = 8,294,400 total pixels.

This assumes that the minimum camera resolution must be 8.3 Mpix. It is not guaranteed that the camera reaches 4K resolution, however, it is a basic recognition. For example, a camera with an IMX546 sensor has a resolution of 2856 x 2848 pixels. While the height of the sensor richly meets the conditions of 4K, the width does not. Even so, for our comparison I will use this camera because for certain types of projects (e.g. square object observation), it is more efficient than a 10.7 Mpix camera with a resolution 3856 x 2764 pixels.

Of course, 4K resolution isn’t the only parameter to consider when you are choosing a camera. Shutter type, frame rate and sensor size are also incredibly important and dictated by your application. And, of course, you must factor price into your decision.

Basic comparison

Sensor Mpixel Shutter Size Width Height Framerate Pricing
MT9J003 10.7 Rolling Shutter / Global Reset 1/2.35 3856 2764  

7.3

 

$
IMX267 8.9 Global 1 4112 2176 31.9 $$
IMX255 8.9 Global 1 4112 2176 42.4 $$$
IMX226 12.4 Rolling Shutter / Global Reset 1/1.7

 

4064 3044 30.7 $
IMX546 8.1 Global 2/3 2856 2848 46.7 $$$
IMX545 12.4 Global 1/1.1 4128 3008 30.6 $$$$

 

Shutter
Rolling shutter and global shutter are common shutter types in CMOS cameras. A rolling shutter sensor has simpler design and can offer smaller pixel size. It means that you can use lower cost lenses, but you must have in mind that you have limited usage with moving objects. A workaround for moving objects is a rolling shutter with global reset functionality which helps eliminating the image distortion.

Frames Per Second
The newest sensors offer a higher frame rate than the USB interface can handle. Check with the manufacturer; not everyone is able to get the listed framerate because of technical limitations caused by the camera.

Sensor Size
Very important information. Other qualitative information should also be considered, not only of the camera but also of the lens used.

Price
Global shutter image sensors are more expensive than rolling shutter ones. For this reason, the prices of global shutter cameras are higher than the rolling shutter cameras. It is also no secret that the image sensor is the most expensive component, so it is understandable that the customer very often bases the decision on the sensor requirements.

Advanced comparison

Sensor Pixel size EMVA report Dynamic range SNR Preprocessing features
MT9J003 1.67 link 56.0 37.2 *
IMX267 3.45 link 71.0 40.2 **
IMX255 3.45 link 71.1 40.2 ***
IMX226 1.85 link 69.2 40.3 **
IMX546 2.74 link 70.2 40.6 ****
IMX545 2.74 link 70.1 40.3 ****

 

There are many other advanced features you can also consider based on your project, external conditions, complexity of the scene and so on. These include:

Pixel Size
Sensor size from the basic comparison is in direct correlation with the size of the pixel because the size of the pixel multiplied by the width and height gives you the size of the sensor itself.

EMVA Report
EMVA 1288 is great document comparing individual sensors and cameras. In case you want the best possible image quality and functionality of the whole system, comparison is an important component in deciding which image sensor will be in your chosen camera. EMVA 1288 is the standard for measurement and presentation of specifications for machine vision sensors and cameras. This standard determines properties like signal-to-noise ratio, dark current, quantum efficiency, etc.

Dynamic Range
Dynamic range is one of the basic features and part of EMVA 1288 report as well. It is expressed in decibels (dB). Dynamic range is the ratio between the maximum output signal level and the noise floor at minimum signal amplification. Simply, dynamic range indicates the ability of a camera to reproduce the brightest and darkest portions of an image.

SNR
Signal-to-noise ratio (SNR) is a linear ratio between recorded signal and total root mean squared noise. SNR describes the data found in an image. It establishes an indication as to the signal quality found in the image indicating with what amount of precision machine vision algorithms will be able to detect objects in an image.

 

Preprocessing Features

Do you build high-end product? Is the speed important for you?
You need to rely on the camera/image sensor features. Every update of an image sensor comes with more and more built-in features. For example:

  • Dual trigger, where you set two different levels of exposure and gain and each can be triggered separately.
  • Self-trigger – you set 2 AOI, the first one triggers image and second detects difference in the AOI.
  • Short exposure modes – you can set as fast as 2us between shutters.

Machine vision components continue to be improved upon and new features are added regularly. So, when you are selecting a camera for your application, first determine what features are required to meet your application needs. Filter to only the cameras that can meet those needs and use their additional features to determine what more you can do.

Machine Vision: 5 Simple Steps to Choose the Right Camera

The machine vision and industrial camera market is offering thousands of models with different resolutionssizes, speeds, colors, interfaces, prices, etc. So, how do you choose? Let’s go through 5 simple steps which will ensure easy selection of the right camera for your application. 

1.  Defined task: color or monochrome camera  

2.  Amount of information: minimum of pixels per object details 

3.  Sensor resolution: formula for calculating the image sensor 

4.  Shutter technology: moving or static object 

5.  Interfaces and camera selector: lets pick the right model 

STEP 1 – Defined task  

It is always necessary to start with the size of the scanned object (X, Y), or you can determine the smallest possible value (d) that you want to distinguish with the camera.

For easier explanation, you can choose the option of solving the measurement task. However, the basic functionality can be used for any other applications.

In the task, the distance (D) between the centers of both holes is determined with the measurement accuracy (d). Using these values, we then determine the parameter for selecting the right image sensor and camera.

Example:
Distance (D) between 2 points with measuring accuracy (d) of 0.05 mm. Object size X = 48 mm (monochrome sensor, because color is not relevant here)

Note: Monochrome or color?
Color sensors use a Bayer color filter, which allows only one basic color to reach each pixel. The missing colors are determined using interpolation of the neighboring pixels. Monochrome sensors are twice as light sensitive as color sensors and lead to a sharper image by acquiring more details within the same number of pixels. For this reason, monochrome sensors are recommended if no color information is needed.

STEP 2 – Amount of information

Each type of application needs a different size of information to solve. This is differentiated by the minimum number of pixels. Lets again use monochrome options.

Minimum of pixels per object details

  • Object detail measuring / detection       3
  • Barcode line width                                           2
  • Datamatrix code module width                4
  • OCR character height                                    16

Example:
The measuring needs 3 pixels for the necessary accuracy (object detail size d). As necessary accuracy (d) which is 0.05 mm in this example, is imaged on 3 pixels.

Note:
Each characteristic or application type presupposes a minimum number of pixels. It avoids the loss of information through sampling blurs.

STEP 3 – Sensor resolution

We already defined the object size as well as resolution accuracy. As a next step, we are going to define resolution of the camera. It is simple formula to calculate the image sensor.

S = (N x O) / d = (min. number of pixels per object detail x object size) / object detail size

Object size (O) can be describe horizontally as well as vertically. Some of sensors are square and this problem is eliminated 😊

Example:
S = (3 x 48 mm) / 0.05 mm = 2880 pixels

We looked at the available image sensors and the closest is a model with resolution 3092 x 2080 => 6.4Mpixels image sensor.

Note:
Pay attention to the format of the sensor.

For a correct calculation, it is necessary to check the resolution, not only in the horizontal but also in the vertical axis.

 

STEP 4 – Shutter technology

Global shutter versus rolling shutter.

These technologies are standard in machine vision and you are able to find hundreds of cameras with both.

Rolling shutter: exposes the motive line-by-line. This procedure results in a time delay for each acquired line. Thus, moving objects are displayed blurrily in the resulting motive through the generated “object time offset” (compare to the image).

Pros:

    • More light sensitive
    • Less expensive
    • Smaller pixel size provides higher resolution with the same image format.

Cons:

    • Image distortion occurs on moving objects

Global shutter: used to get distortion-free images by exposing all pixels at the same time.

Pros:

    • Great for fast processes
    • Sharp images with no blur on moving objects.

Cons:

    • More expensive
    • Larger image format

Note:
The newest rolling shutter sensors have a feature called global reset mode, which starts the exposure of all rows simultaneously and the reset of each row is released simultaneously, also. However, the readout of the lines is equal to the readout of the rolling shutter: line by line.

This means the bottom lines of the sensor will be exposed to light longer! For this reason, this mode will only make sense, if there is no extraneous light and the flash duration is shorter or equal to the exposure time.

STEP 5 – Interfaces and camera selector

Final step is here:

You must consider the possible speed (bandwidth) as well as cable length of camera technology.

USB2
Small, handy and cost-effective, USB 2.0 industrial cameras have become integral parts in the area of medicine and microscopy. You can get a wide range of different variants, including with or without housings, as board-level or single-board, or with or without digital I/Os.

USB3/GigE Vision
Without standards every manufacturer does their own thing and many advantages customers learned to love with the GigE Vision standard would be lost. Like GigE Vision, USB3 Vision also defines:

    • a transport layer, which controls the detection of a device (Device Detection)
    • the configuration (Register Access)
    • the data streaming (Streaming Data)
    • the handling of events (Event Handling)
    • established interface to GenICam. GenICam abstracts the access to the camera features for the user. The features are standardized (name and behavior) by the standard feature naming convention (SFNC). Additionally, it is possible to create specific features in addition to the SFNC to differentiate from other vendors (quality of implementation). In contrast to GigE Vision, this time the mechanics (e.g. lockable cable connectors) are part of the standard which leads to a more robust interface.

I believe that these five points will help you choose the most suitable camera. Are you still unclear? Do not hesitate to contact us or contact me directly: I will be happy to consult your project, needs or any questions.