next up previous contents
Next: 5.3 Filter Up: 5. Image processing menus Previous: 5.1 Capture   Contents


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 up previous contents
Next: 5.3 Filter Up: 5. Image processing menus Previous: 5.1 Capture   Contents
John Cupitt 2003-07-21