The ‘
Frames per second for live preview
’ setting means the frame rate of the live
preview and does not affect the frame rate of the image stream from the camera. The only
thing you need to be aware of with this setting is that it must be at or below the maximum
FPS for your chosen image size and camera stream format or you will get the warning
messages referred to above when you apply the settings. Bear in mind that this is a
maximum possible frame rate – the actual number of frames per second of the live
preview will depend on the actual receive frame rate from the camera and the depends on
other factors such a the exposure setting, the speed and processing power of the host
computer and the current speed of the USB connection to the camera.
The ‘
Format stream from the camera
’ setting is only one of two choices: MJPEG or
YUYV, the latter being a raw uncompressed image stream from the camera and so having
a slower maximum frame rate. The MJPEG option is best for live previews, the YUYV
option is best for optimum image quality in the captured images. The AF51 supports both
of these options. If you use a camera that only supports one or the other then you will not
be able to change to the unsupported option.
The ‘
Format to save the image files to disk as
’ is the format any saved images will be
saved as. The ‘save-as’ options and their meanings are as follows:
Raw YUYV
– This is the YUYV frame direct from the camera. The saved file will have an
ending of the form ‘_yuyv.raw’. This will be a raw array of unsigned integers at 16 bits per
pixel (bpp), i.e. unsigned shorts. There will be 1 integer for every pixel so the array will be
if total size: height x width integers. The integers will be arranged in raster fashion from
top left (pixel [0]) to bottom right (pixel [(height x width) - 1]). Each 16 bit integer will
contain two 8 bit values: the first byte is a luminance value and the second byte is a colour
value (the first colour value from a pair of pixels is Cb1 from the first pixel and Cr1 from the
second pixel). This means that a full colour value will only be available for half the total
number of pixels, each full colour value pair (the Cb1,Cr1 pair) being applied to the two
contiguous pixel positions from which their components were derived. There will be no
header information saved (neither an internal header nor an external header filed).
Because this just dumps the raw data off the camera it requires no colour conversion pre-
process so it is the quickest method to grab an image from the YUYV stream but for the
same reason it has the following restrictions. This save-as format will not be allowed when
the camera stream format is MJPEG. If you select this option when the camera is
strsaming in MJPEG format and try to save an image you will get a pop up error telling
you it cannot be saved. You will not be allowed to do multi-frame averaging, masking,
dark field correction or flat field correction when using this raw YUYV format. The options
to save a raw doubles or FITS version of the file (to be discussed later) will be ignored –
no such files will be saved even if you check the box to save them.
OptArc AF51 Camera Page 74 of 99 User Guide v1.02
