The histogram
=============

Below the frame buffer viewer, the histogram plots the
distribution of pixel values in the current frame --
or, when a region is selected in the frame buffer, in
just that region. It updates live with the preview, so
you can read what the camera sees numerically: what
colour an object is, how much it varies, and how it
separates from the background.

The histogram is one of five views the pane can show;
the selector at the left of its title bar switches
between them. *Board Info* lists what the connected
camera is -- board, sensor, firmware and bootloader
versions, memory sizes, and capabilities -- which is
the information to quote in a support request.
*Memory* graphs the camera's memory use while the
script runs. *Statistics* counts the packets, errors,
and channel events on the link to the camera, for
diagnosing a connection that misbehaves. *Channels*
shows the readouts and controls the product's script
publishes, covered on :doc:`its own page <channels>`.
The IDE's :doc:`pane views <../ide/pane-views>` page
describes each in more detail.

.. figure:: ../ide/figures/histogram.png
   :class: framed
   :alt: The histogram pane in RGB for a thermal image, with one filled plot per channel and the mean, median, mode, standard deviation, minimum, maximum, and quartile statistics under each

   The histogram in RGB: one plot per channel with its
   statistics underneath.

The selector in the pane's title bar chooses the colour
space the statistics are computed in: RGB, Grayscale,
LAB, or YUV. Each channel gets its own plot, with the
channel's statistics underneath: mean, median, mode,
standard deviation, minimum, maximum, and the lower and
upper quartiles. Select a region in the frame buffer to
read the values of one object instead of the whole
scene.

The focus number
----------------

The frame buffer's title line ends with a focus metric
-- a sharpness score computed from the image.
Its absolute value means nothing; its *direction* means
everything. While adjusting a lens, watch the number:
it rises as the image gets sharper and peaks at best
focus. Point the camera at a detailed target at the
working distance, turn the lens slowly, and stop at the
maximum.