Optimizing Image Quality
Different applications have different requirements in
terms of image quality. By adjusting some settings using the pylon
Viewer you can achieve good results quickly.
Focus
To get a focused image, consider the following:
- The lens must be screwed into the lens mount as far as it will
go.
- The glass surfaces of the lens must be clean.
- The target object must be within the range of focus of the lens.
If your objects are located at different distances from the camera,
you must consider depth of focus. The depth of focus must be sufficiently
deep to allow all objects to appear focused.
- Closing the lens aperture (turning the aperture ring to higher
f-numbers) increases the depth of focus and vice versa.
- Closing the aperture decreases the amount of light reaching the
camera’s sensor and therefore results in a darker image.
Brightness
The following factors determine the brightness of an image:
Illumination
- Basler recommends the use of bright illumination if possible, but
to avoid excessive intensity. This will prevent you from having to
operate the camera using extreme camera settings.
- In images acquired from CCD sensors, excessive brightness
will cause artifacts such as smear (white stripes in the image) and
blooming (local over-saturation that destroys contrast). You can decrease
the proneness to smear and blooming by choosing a diffuse and less
intense illumination.
- If illumination of sufficient brightness is not available, you
can select a lens that is optimized for light utilization.
Lens Aperture
- Opening the lens aperture allows more light to reach the camera’s
sensor and therefore increases the brightness of the image.
- Opening the lens aperture also increases the effects of optical
aberrations. This causes image distortions and the intensity of light
decreases towards the edges of the sensor (vignetting). In addition,
the depth of focus decreases.
Exposure Time
- You can increase the brightness of the image by increasing the
camera’s Exposure Time setting. This
increases the amount of photons collected for pixel readout.
- Increasing the exposure time setting may decrease the camera's
frame rate. If you are acquiring images of moving objects, increasing
the exposure time setting may increase motion blur.
Gain
- Increasing the camera's Gain setting will
also increase image brightness.
- Unless your application requires extreme contrast, you should make
sure that detail remains visible in the brightest portions of the
image.
- Image noise is increased by increasing gain.
Black Level
- You can change the brightness of the image by changing the camera’s
Black Level setting.
- Normally, you should increase the black level setting only as far
as is necessary to make detail visible in the darkest portions of
an image.
Exposure Time
The exposure time setting determines the time interval during which
the sensor is exposed to light.
Choose an exposure time setting that takes account of whether you want
to acquire images of still or moving objects:
- If the object is not moving, you can choose a
high exposure time setting. High exposure time settings may reduce
the camera’s maximum allowed acquisition frame rate and may cause
artifacts to appear in the image.
- If the object is moving, choose a low exposure
time setting to prevent motion blur. As a general rule, choose a short
enough exposure time to make sure that the image of the object does
not move by more than one pixel during exposure.
Gain
Gain amplifies each pixel readout by a certain factor. Accordingly,
signal and noise are both amplified.
- Increasing gain will increase the image contrast.
- Increasing gain will increase the image brightness.
Unless your application requires
extreme contrast, make sure that detail remains visible in the brightest
portions of the image when increasing gain.
Contrast
Strong contrast in an image is obtained when objects of different brightnesses
are represented by strongly different gray values. For most applications,
optimum contrast is achieved when the image displays a wide range of gray
values with fine detail remaining visible even in the darkest and brightest
parts of an image. Some applications, however, may require extreme contrast.
- You can increase the contrast in the image by increasing the camera’s
gain setting. Gain amplifies the pixel readout.
- High black level settings will prevent high contrast. Basler recommends
not to exceed a black level setting of 64 (at greater than 8 bit output).
- In images acquired from CCD sensors, contrast can be destroyed
by local over-saturation (blooming) if the image brightness is too
high. You can decrease the proneness for smear and blooming by choosing
a diffuse and less intense illumination.
- Closing the lens aperture not only decreases image brightness but
also increases contrast towards the edges of an image.
- If you must use insufficient illumination resulting in dark
images, you may notice the blurring influence of noise. If you operate
the camera near the top end of its specified temperature range, the
effects may be particularly noticeable. You can increase contrast
by lowering the operating temperature of the camera.
Note that it is
not possible to improve the signal-to-noise ratio by increasing gain.
Increasing the gain will increase both signal and noise in equal proportions.
White Balance
- If you are using a color camera, the object that you use when adjusting
the white balance should be a uniform gray and should fill the camera’s
entire field of view. Your white balance will be correct when images
of this object show a uniform gray.
- Changing the black level setting will also change the white balance.
Basler therefore recommends that you check the white balance after
setting the black level.
- Make sure the image is neither underexposed nor overexposed when
checking the white balance.