The Pixel Toolbar

The pixel bar contains useful information about the current pixel that
the mouse is located on, together with the zoom factor currently used
to display the image.
The x1 box
displays the current Zoom Factor.
Next to it are the X and
Y coordinates of the current cursor location.
Afterwards comes the current pixel color value as an RGBA float or as 8 bits or as 8 bits hex.
Then comes the current pixel value in HSV (Hue,
Saturation, Value). You can also select it to change it to display:
HSL (Hue, Saturation, Luminance)
CIE XYZ
CIE xyY
CIELab L*a*b
CIELuv L*u*v
YUV Pal
YDbDr Secam/PalN
YIQ NTSC
ITU-601 Digital Pal/NTSC
ITU.702 Digital HDTV
Finally, the current pixel's Rec.709 Luminance (Y) Y = 0.2126 R + 0.7152 G + 0.772 B
is also shown.
You can change it to display:
Lumma Y' = ( R + G + B / 3 )
Lightness L = (116 * Y ^ 1/3 ) / 100
The pixel toolbar can be toggled on and off by using the F2 hotkey.