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<h1>The Image Window</h1>
<p>Note: unless explicitly stated otherwise, the term <i>click</i>
means "click with the Left mouse button."</p>
<p>Start the program up by typing ' <tt>xv</tt> '. After a short
delay, a window will appear with the default image (the <i>xv</i>
logo, credits and revision date) displayed in it. If you change
the size of the window (using whatever method your window manager
provides), the image will be automatically stretched to fit the
window.</p>
<p><img src="images/fig-002.gif" width="494" height="300"><br>
</p>
<h2><a name="displaying-pixel-values">Displaying Pixel Values</a></h2>
<p>Clicking (and optionally dragging) the Middle mouse button
inside this window will display pixel information in the
following format:</p>
<p><tt>196, 137 = 191,121,209 #bf79d1 (287 42 81 HSV) [ 0, 0]</tt></p>
<p>The first pair of numbers (196,137) are the <i>x</i> and <i>y</i>
positions of the cursor, in image <a name="pixel-coordinates">coordinates</a>.
These numbers remain the same regardless of any image resizing,
or cropping; a 320x200 image remains a 320x200 image, regardless
of what size it is displayed on the screen.</p>
<p>The first triplet of numbers (191,121,209) are the RGB values
of the selected pixel. The components will have integer values in
the range 0-255. The values displayed are prior to any HSV/RGB
modification, but after any colormap changes. See "<a
href="color-editor-1.html">The Color Editor</a>" for
details.</p>
<p>The next item is a six-digit value expressing the RGB values
of the selected pixel in hex, in the #rrggbb format. This is the
same format used to specify colors to other X programs, which may
be useful.</p>
<p>The second triplet of numbers (287 42 81) are the HSV values
of the selected pixel. The first component will have integer
values in the range 0-359, and the second and third components
will have integer values in the range 0-100. The values displayed
are prior to any HSV/RGB modification, but after any colormap
changes. See "<a href="color-editor-1.html">The Color Editor</a>"
for details. Also, see "<a href="rgb-hsv-colorspaces.html">RGB
& HSV Colorspaces</a>" for more information about what
these numbers mean.</p>
<p>Finally, the last pair of numbers is the <a
name="pixel-distance">distance</a> (dx, dy) between the current
mouse position and where the mouse was originally clicked. </p>
<p>Note: If you actually want to measure some pixels, it will
probably help to zoom in on a the relevant portion of the image,
to the point that you can see the individual pixels. See "<a
href="image-window.html#zooming">Zooming</a>" below.</p>
<p>Note: This also sets the 'current color' value used by various
painting tools. (See "<a href="image-window.html#editing">Image
Editing</a>" .)</p>
<p>This string is automatically copied to your X server's cut
buffer whenever you measure pixel values. This lets you easily
feed this information to another program, useful if you're doing
manual feature extraction, or something. Try it: measure a
pixel's value, and then go click your Middle mouse button in an <i>xterm</i>
window.</p>
<h2><a name="selection-rectangle">Selection Rectangle</a></h2>
<p>Bring up the <i>xv controls</i> window by pressing the <b>?</b>
key or clicking the Right mouse button inside the image window.</p>
<p>Clicking and dragging the Left button of the mouse inside the
image window will allow you to draw a selection rectangle on the
image. If you're unhappy with the one you've drawn, simply click
the Left button and draw another. If you'd like the rectangle to
go away altogether, click the Left button and release it without
moving the mouse.</p>
<p>Double-clicking the Left button inside the image window will
create a selection rectangle the size of the currently displayed
area of the image, or remove the previous selection as
appropriate.</p>
<p>Once a selection rectangle has been drawn, it can be <a
name="selection-resize">fine-tuned </a>by clicking and dragging
any of the handles that appear on its edge. If you press the <<b>Shift</b>>
key while dragging a handle, the selection rectangle is kept
square. If you press the <<b>Ctrl</b>> key while dragging a
handle, the selection rectangle maintains the same aspect ratio
it originally had.</p>
<p>You can <a name="selection-move">move</a> the selection
rectangle by Left-clicking inside it and dragging it around.
Pressing the <<b>Shift</b>> key while doing so will
constrain the motion to the horizontal and vertical axes.</p>
<p>You can determine how large the selection rectangle is (in
image coordinates) by bringing up the <i>xv info</i> window. Do
this selecting <b>Image Info</b> from the <b>Windows</b> menu <i>xv
controls</i> window or by pressing the <b>i</b> key inside any
open <i>xv</i> window.</p>
<p>The <i>xv info</i> window will display, among other things,
the current size and position of the selection rectangle in terms
of image coordinates. For example, if it says:</p>
<blockquote>
<p><tt>114x77 rectangle starting at 119,58</tt></p>
</blockquote>
<p>it means that the current selection rectangle is 114 image
pixels wide, 77 image pixels high, and that its top-left corner
is located 119 image pixels in from the left edge of the image,
and 58 image pixels in from the top edge. These values will be
updated as you drag the cropping rectangle around.</p>
<p>If you want to set the size or position of the selection
rectangle <a name="selection-fine-tune">precisely</a>, you can
use the arrow keys on your keyboard. First, make the <i>xv info</i>
window visible as described above. Second, use the mouse to draw
a rough approximation of the selection rectangle that you want.
You can now use the arrow keys to move the selection rectangle
around the image. Once you've gotten the top and left sides of
the selection rectangle precisely where you want them, you can
move the bottom-right corner of the selection rectangle by
holding the <b><Shift></b> key down while using the arrow
keys. Pressing the up arrow will make the rectangle shorter, and
pressing the down arrow will make the rectangle taller. </p>
<h2><a name="cropping">Cropping</a></h2>
<p>Once you have a selection rectangle that you can live with,
you can proceed with the actual cropping operation. Click the <b>Crop</b>
button in the <i>xv controls</i> window, or press the <b>c</b>
key in any open <i>xv</i> window. The image window will shrink to
show only portions of the image that were inside the cropping
rectangle.</p>
<p>Note: if you are running a window manager such as <i>mwm</i>,
which decorates windows with a title bar, resizing regions, and
such, it is quite possible that the aspect ratio of the cropped
image will get screwed up. This is because certain window
managers enforce a minimum window size. If you try to crop to a
rectangle that is too small, the window manager will create the
smallest window it can, and the image will be stretched to fit
this window. If this happens, you can press the <b>Aspect</b>
button in the <i>xv controls</i> window, or press the <b>a</b>
key in any open <i>xv</i> window. This will expand the image so
that it will once again have the correct aspect ratio. (Also, see
the ' <tt>-nodecor</tt> ' option, in "<a
href="modifying-behavior-3.html#miscellaneous-options">Miscellaneous
Options</a>".)</p>
<p>You can crop a cropped image by repeating the same steps
(drawing a new selection rectangle and issuing the <b>Crop</b>
command), ad infinitum.</p>
<p>You can return to the original, uncropped image by using the <b>UnCrop</b>
command. Simply click the <b>UnCrop</b> button or press the <b>u</b>
key in any open <i>xv</i> window. Note that using the <b>UnCrop</b>
command will turn off image smoothing (the <b>Smooth</b>
command), due to the potentially long time it can take to
generate a large, smoothed image.</p>
<p>Note that if you try to make the selection rectangle too small
in either width or height (under 5 screen pixels), it'll just
turn itself off. If you want to crop a very small portion of an
image, you'll probably have to do it in two passes. First, crop
to a smallish rectangle, expand that image, then crop again.</p>
<p>You can also <a name="cropping-fine">fine-crop</a> the image
by pressing the <b><Ctrl></b> key and one of the arrow
keys. This will crop off one pixel from the edge of the image,
based on the arrow key pressed. The <b>Up</b> key moves the
bottom edge up one pixel, the <b>Down</b> key moves the top edge
down one pixel, and so on.</p>
<h2><a name="zooming">Zooming</a></h2>
<p>You can <a name="zoom-in"><b>Zoom In</b></a> by a factor of
two (or four, or eight, etc.) on any rectangular region of the
image by holding down the <<b>Ctrl</b>> key on your
keyboard and clicking the Left mouse button in the image window.
A rectangle will appear, centered around the cursor position,
showing you what portion of the image will be expanded. Move the
rectangle as you see fit, release the mouse button, and the
region inside the rectangle will be redrawn at twice its previous
size. The image window should remain the same size. You can
repeat this operation to zoom in by a factor of four, or eight,
or whatever, as many times as you wish.</p>
<p>While zoomed-in, you can <a name="panning"><b>Pan</b></a> the
image around by holding down the <<b>Ctrl</b>> key,
clicking the Middle mouse button in the image window, and
dragging it around. A rectangle will appear around the mouse,
indicating where the currently-displayed portion of the image
will be moved to.</p>
<p>You can <a name="zoom-out"><b>Zoom Out</b></a> by a factor of
two (if possible) by holding down the <b><Ctrl></b> key and
clicking the Right mouse button inside the image window. You can
not zoom out beyond the point where the entire image fills the
window. </p>
<h2><a name="multi-page-documents">Multi-Page Documents</a></h2>
<p><i>xv</i> now has the ability to display multi-page image
files, though currently this is only implemented for PostScript
files (using the <i>ghostscript</i> interpreter). If you are
viewing a multi-page document, a "page <i>n</i> of <i>m"</i>
string will be added to the <i>xv image</i> window's title bar.</p>
<p>You can walk through the document by pressing the <b><PageUp></b>
and <b><PageDown></b> keys on your keyboard (they may be
labeled <<strong>Prev</strong>> and <<strong>Next</strong>>'
instead) while the keyboard focus is on the <i>xv image</i>
window. Pressing <b><Shift-Up></b> and <b><Shift-Down></b>
may also work.</p>
<p>You can also jump directly to any given page by typing '<b>p</b>'
into the <i>xv image </i>window. This will pop up a dialog window
which will ask you what page you'd like to go to.</p>
<h2><a name="editing">Image Editing</a></h2>
<p><i>xv</i> now features a number of rudimentary image-editing
tools. While it isn't about to compete with Adobe's <i>PhotoShop</i>
anytime soon, you may still find what it does to be of some use.
You now have the ability to do pixel-editing, freehand
'scribbling', line drawing, and pixel-level 'smudging'. Also, <i>xv</i>
now supports cut, paste, copy, and clear of rectangular
selections, as described in "<a
href="control-window-4.html#cut-paste-commands">Image Cut and
Paste Commands</a>" . Also, <i>xv</i> now has a 'text
annotation' tool, described in "<a
href="control-window-5.html#text-annotation">Text Annotation</a>"
.</p>
<p>The major weakness: the various drawing tools listed above <i>can</i>
<i>only draw in colors that already exist in the image</i>. At
this time, these tools (and <i>xv</i>) are primarily focused on
the 'image editing' job, rather than on the 'arbitrary paint
program' job. Needless to say, there's still a way to paint in
whatever color you'd like. It's just a matter of getting the
desired color(s) into the picture. The best way is probably to
use the <b>Pad</b> command (see "<a
href="control-window-4.html#pad-command">The Pad Command</a>").</p>
<h3><a name="pixel-editing-line-drawing">Pixel Editing and Line
Drawing</a></h3>
<p>All of the following drawing commands use the concept of the
'current color'. The current color is set by using the Middle
mouse button in the image window to 'pick up' the desired color.</p>
<p>You can edit individual pixels by doing a shift-middle-click
with the mouse. (Hold a <<b>Shift</b>> key, and
Middle-click somewhere in the image window.) The selected pixel
will change to the desired color. It will probably help to zoom
in on the relevant section of the image first. Anyway, if you
drag the mouse around, you will be able to draw arbitrary
'scribbles' all over the image. This probably isn't desirable, so
be careful!</p>
<p>You can also draw straight lines by holding down the <<b>Ctrl</b>>
key along with the shift-middle combination.</p>
<h3><a name="pixel-smudging">Pixel Smudging</a></h3>
<p>You can 'smudge' specific areas of the image by doing a
shift-right-click with the mouse, in the image window. The
clicked-on pixel will be replaced with the average color of the 9
pixels in the 3x3 square centered on said pixel. This can be used
to manual edit out 'salt and pepper' noise. It can also be used
to soften edges. As with the pixel editing tool, you can drag the
'smudger' around.</p>
<p>Note: This only works in '24-bit' mode. If you are viewing an
8-bit image, it will be automatically converted up to a 24-bit
version of itself.</p>
<p>Note: While this tool is similar to the <b>Blur</b> and <b>DeSpeckle</b>
algorithms, those algorithms operate on <i>every</i> pixel in a
rectangular region, whereas this tool operates only on those
pixels that you click or drag on.</p>
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