||The RGB Modification tool is a collection of
three graph windows, each of which operate on one of the
components of the RGB colorspace. This tool lets you
perform global color-correction on the image by boosting
or cutting the values of one or more of the RGB color
components. You can use this to correct for color screens
that are 'too blue', or for color printers that produce
'brownish' output, or whatever.
The graphs work exactly
as explained in "The Intensity
Neat Trick: In addition to color-correction, you can
use the RGB modification tool to add color to images that
didn't have color to begin with. For instance, you can
'pseudo-color' a greyscale image.
An example of pseudo-coloring:
- Adjust the Red graph so that there is a strong red
presence on the right side of the graph, and none on the
left, or in the middle.
- Adjust the Green graph so that there is a strong
green presence in the middle of the graph, and none on
the left or right.
- Adjust the Blue graph so that there is a strong
blue presence on the left side of the graph, and none on
the left, or in the middle.
- The graphs should look roughly like this:
You now have a transformation that will take greyscale images
and display them in pseudo-color, using a 'temperature' color
||These buttons provide general control
over the whole xv color editor window. You can
display the image with or without color modification,
save and recall presets, and undo/redo changes. Also,
convenience controls are given for performing some of the
most common operations on the Intensity graph.
- Displays the image using the current HSV and RGB
Modifications. Also turns the 'Display with HSV/RGB
mods' checkbox on. (See below.) This is only useful
when the 'Auto-apply HSV/RGB mods' checkbox is
Keyboard Equivalent: <Meta> a
- Displays the image without any HSV or RGB Modifications.
Also turns the 'Display with HSV/RGB mods'
- Undoes the last change to the HSV or RGB controls.
may be helpful to think of xv as maintaining a
series of 32 'snapshots' of the HSV and RGB controls. You
are normally looking at the last frame in this series.
The Undo control moves you backwards in the
- Only available after you've hit Undo . Moves you
forward in the 'snapshot' series described above. Note
that if you have hit Undo a few times (i.e.,
you're now looking at some frame in the middle of the
series), and you change an HSV or RGB control, all
subsequent frames in the series are thrown away, and the
current state becomes that last frame in the series.
- Resets all HSV and RGB controls to their default
settings. Doesn't affect the Colormap Editing
tool. Note that these default settings can be changed
using the Set command described below.
Keyboard Equivalents: R , <Meta> r ,
and <Meta> 0
- Pressing any of these buttons recalls a preset (a
complete set of values for the HSV and RGB controls). By
default, the presets are:
- Binary intensity. Every color in the image is
either at full brightness, or black. Gives images
a neat 'neon' sort of look, much like the Saturday
Night Live credits of the late-70's.
- Binary colors. The image will be shown using only
the 8 binary combinations of red, green, and
blue. (e.g. black, blue, green, cyan, red,
magenta, yellow, white)
- Temperature pseudo-color. (For use on greyscale
images) Maps intensity values 0-255 into a
'temperature' color scheme where blue is
'coldest' and red is 'hottest'.
- Map pseudo-color. (For use on greyscale images)
Maps intensity values 0- 255 into something akin
to the standard 'elevation map' color scheme
(blue, green, yellow, brown)
Of course, you can replace these defaults with your
own. See "Modifying
xv Behavior" for more details.
Keyboard Equivalents: <Meta> 1 , <Meta>
2 , <Meta> 3 , and <Meta> 4
- Used in conjunction with the Reset, 1, 2,
3, or 4 buttons to store the current
settings of the HSV and RGB controls into a preset. To do
so, press the Set button, and then press one of
the Reset, 1, 2, 3, or 4
buttons. The current HSV and RGB control settings will be
stored in that preset, as long as xv continues
running. The values will be lost when the program exits.
It is also possible to save these values permanently. See
the CutRes button (below) and "Modifying
xv Behavior" for more details.
- Copies the current settings of the HSV and RGB controls,
as text, into the X server's cut buffer. You can then use
a text editor to paste these values into your '.Xdefaults'
(or '.Xresources') file. This lets you save the
current settings 'permanently'. See "Modifying
xv Behavior" for more details.
- This button closes the xv color editor window.
- Brightens the image by moving all the handles in the Intensity
graph up by a constant amount.
- Darkens the image by moving all the handles in the Intensity
graph down by a constant amount.
- Increases the contrast of the image by moving handles on
the left side of the Intensity graph down, and
handles on the right side up.
- Decreases the contrast of the image by moving handles on
the left side of the Intensity graph up, and
handles on the right side down.
- Normalizes the image so that the darkest pixels in the
image are given an intensity of '0', and the brightest
pixels are given an intensity of '255'. Intermediate
colors are interpolated accordingly. This forces the
image to have the full (maximum) dynamic range.
Keyboard Equivalent: N
- Runs a histogram equalization algorithm on the currently
displayed region of the image. That is, if you're
cropped, it will only run the algorithm on the cropped
section. Note, however, that the only modification it
makes to the image is to generate a bizarre corrective Intensity
curve. As such, if you HistEq a section of the
image, the rest of the image will probably not be what
you'd want. Also note that the histogram curve will 'go
away' if you touch any of the handles in the Intensity
graph window, just like a 'gamma' curve would.
Keyboard Equivalent: H
- The 'Display with HSV/RGB mods' checkbox tells you
whether or you're looking at a modified image (checked)
or the 'raw', unmodified image (unchecked). The Apply
and NoMod buttons change the setting of this
checkbox, and you can also change the checkbox directly
by clicking on it.
- The 'Auto-apply HSV/RGB mods' checkbox controls
whether or not the program regenerates and redisplays the
image after each change to an HSV or RGB control. By
default, this checkbox is turned on, so that you can
easily see the results of your modifications. However, if
you want to make a large number of changes at once, it
might be preferable to turn automatic redisplay off for a
while, to speed things up.
- The 'Auto-apply while dragging' checkbox controls
whether or not the image colors are changed automatically
as you manipulate the various xv color editor
dials and graphs. This button is normally turned on, but
for it to have any effect, you must be in 'Read/Write
Colors' mode. See "Color
Allocation Commands" and the '-rw' mode
described in "Color
Allocation Options" for more information.
- The 'Auto-reset on new image' checkbox controls
whether or not the HSV and RGB controls are Reset
back to their default values whenever a new image is
loaded up. By default, this is also turned on, as when
you're playing with the HSV/RGB controls, you probably
only want to affect the current image, and not all
subsequently loaded images as well.