Operator Reference
cfa_to_rgb (Operator)
cfa_to_rgb — Convert a single-channel color filter array image into an RGB image.
Signature
cfa_to_rgb(CFAImage : RGBImage : CFAType, Interpolation : )
Description
cfa_to_rgb converts a single-channel color filter array
image CFAImage into an RGB image RGBImage. Color
filter array images are typically generated by single-chip CCD
cameras. The conversion from color filter array image to RGB image
is typically done on the camera itself or is performed by the device
driver of the frame grabber that is used to grab the image. In some
cases, however, the device driver simply passes the color filter
array image through unchanged. In this case, the corresponding
HALCON frame grabber interface typically converts the image into an
RGB image. Hence, the operator cfa_to_rgb is normally used
if the images are not being grabbed using the HALCON frame grabber
interface (grab_image or grab_image_async), but are
grabbed using function calls from the frame grabber SDK, and are
passed to HALCON using gen_image1 or
gen_image1_extern.
In single-chip CCD cameras, a color filter array in front of the
sensor provides (subsampled) color information. The most frequently
used filter is the so-called Bayer filter. The color filter array
has the following layout in this case:
Each gray value of the input image CFAImage corresponds to
the brightness of the pixel behind the corresponding color filter.
Hence, in the above layout, the pixel (0,0) corresponds to a green
color value, while the pixel (0,1) corresponds to a blue color
value. The layout of the Bayer filter is completely determined by
the first two elements of the first row of the image, and can be
chosen with the parameter CFAType. In particular, this
enables the correct conversion of color filter array images that
have been cropped out of a larger image (e.g., using
crop_part or crop_rectangle1).
The algorithm that is used to interpolate the RGB values is
determined by the parameter Interpolation. For
Interpolation = 'bilinear', a bilinear
interpolation is performed. While this algorithm is very fast, it
typically leads to “zipper-like” artifacts and color artifacts at
strong edges. For Interpolation =
'bilinear_dir', a modified version of the bilinear
interpolation is performed that may lead to fewer zipper-like
artifacts, especially at horizontal or vertical edges in the image.
The results may still exhibit color artifacts at strong edges,
however. The runtime of this algorithm is only slightly longer than
that of bilinear interpolation. For Interpolation =
'bilinear_enhanced', an enhanced version of the bilinear
interpolation is performed that produces fewer zipper-like artifacts
and color artifacts than the other two bilinear algorithms in most
cases. The runtime of this algorithm is significantly longer than
that of the other two algorithms.
If 'mmx_enable' is set to 'true' (and the SIMD
instruction set is available), the internal calculations for byte
images are performed using SIMD technology for
Interpolation = 'bilinear' and
Interpolation = 'bilinear_dir'.
For Interpolation = 'bilinear' and
Interpolation = 'bilinear_dir', cfa_to_rgb
can be executed on OpenCL devices. The width of the input image should be
a multiple of four for byte images, or two for uint2 images, as the
operation will be much slower otherwise.
Execution Information
- Supports OpenCL compute devices.
- Multithreading type: reentrant (runs in parallel with non-exclusive operators).
- Multithreading scope: global (may be called from any thread).
- Automatically parallelized on tuple level.
- Automatically parallelized on domain level.
Parameters
CFAImage (input_object) singlechannelimage(-array) → object (byte* / uint2*) *allowed for compute devices
Input image.
RGBImage (output_object) multichannel-image(-array) → object (byte / uint2)
Output image.
CFAType (input_control) string → (string)
Color filter array type.
Default: 'bayer_gb'
List of values: 'bayer_bg', 'bayer_gb', 'bayer_gr', 'bayer_rg'
Interpolation (input_control) string → (string)
Interpolation type.
Default: 'bilinear'
List of values: 'bilinear', 'bilinear_dir', 'bilinear_enhanced'
Result
cfa_to_rgb returns 2 (
H_MSG_TRUE)
if all parameters are correct. If
the input is empty the behavior can be set via
set_system(::'no_object_result', <Result>:). If necessary,
an exception is raised.
Possible Predecessors
gen_image1_extern,
gen_image1,
grab_image
Possible Successors
See also
Module
Foundation