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5.2 Colour
This menu groups operations on colour calibrated (that is, colorimetric)
images. nip has 10 main types of colorimetric image, see Table 5.1.
All these types are D65 (that is, daylight) absolute colorimetric.
When it displays an image, nip uses the Type field in the image
header as a hint on how to transform the numbers in the image into RGB for
the display. The current Type is displayed at the end of the caption
line below an image thumbnail.
You can also use the Print menu to transform from device space to ICC
profile connection space. You need to be aware of D50 and D65 differences
though.
Table 5.1:
nip colourspaces
Name |
Format |
Notes |
Mono |
One band 8 bit |
Not really calibrated at all |
XYZ |
Three band float |
The base CIE colourspace |
Yxy |
Three band float |
Sometimes useful for colour meters |
Lab |
Three band float |
The 1976 version of the CIE perceptual colourspace |
LCh |
Three band float |
Lab, but with polar coordinates |
UCS |
Three band float |
Highly uniform space from the CMC(l:c) standard |
RGB |
Three band 8 bit |
Screen device space for your current display |
sRGB |
Three band 8 bit |
Screen device space for the sRGB standard |
LabQ |
Four band 8 bit |
Like Lab, but represented as 10:11:11 bits |
LabS |
Three band 16 bit |
Like Lab, but represented as 15:16:16 bits |
|
- Mono_to etc.
- These menu items transform between the colour spaces known by VIPS.
They do the transform you'd expect from the name, and also set the
image Type field.
- Colour_recombination
- This menu item multiplies each pixel in an image through a matrix.
Apply to an image, then open up the widget and adjust the matrix.
It's useful for colour adjustment, and for changing the number of
bands in an image.
- Colour_temperature
- Use these items to switch between D50 and D65 illuminants. Handy with
the items in the Print menu. Uses the Bradford approximation.
- dE_
- Calculate various colour difference metrics. Select two objects and
click on one of the items.
- Tint_mono_image
- Use this to apply a single tint to a black and white image. Apply to
an image, then open up the row and pick the colour you want.
- Adjust_cast
- Use this to adjust the white point of an image in LAB space. Apply
to an image, then open up the row and drag the sliders.
- Adjust_hue_saturation_brightness
- Use this to adjust an image in LCh space. Apply to an image, open up
the row and drag the sliders.
- Similar_colour
- Use this to make a mask image (one containing only 0 and 255), with
255 for pixels which are within a certain distance of a specified
colour. Apply to an image, then open up the row. A region will appear
on the original image which you can drag to indicate the target
colour. Alternatively, edit the target colour directly. You can also
adjust a threshold.
Next: 5.3 Filter
Up: 5. Image processing menus
Previous: 5.1 Capture
  Contents
John Cupitt
2003-07-21