|
An image in Howler is always associated with a swap image
(often used for a scratch pad) and an alpha channel. The alpha
channel is an 8 bit image that can contain a selection or mask
that can be used like a template or artistic friskette.
|
|
The Swap image.
It's like the back side of your paper!
The swap image can be useful in many ways. You can use it to
store a spare copy of an image, or to store a checkpoint for your
work. You can rub one side through to the other, or you can use it
with some filters to displace, merge, composite, or generally
modify your main image.
To swap images, just press the j key. “j” is for
“jump.”
Pressing the J (capital j) key will copy the current image to
the swap image.
|
The current swap status is displayed in the main title bar. It
appears as either (Main) or (Swap) just before the zoom indicator.
|
|
There are menu items under the Image menu for managing your
image, including functions for copying the image to and from the
alpha channel.
Swap images swaps between the Main and Swap images
Copy to
swap copies the current image to the swap image
Copy swap image
to alpha copies the swap image to the Alpha channel, turning it
into a selection mask.
Copy alpha to swap image copies the
image in the alpha channel to the swap image.
These functions are helpful when you need to work on a
selection that is comprised of a bitmap image instead of a
primitive shape, such as a rectangle or ellipse. Another option is
to paint directly on the image using “Paint on alpha”
under the selection menu.
|
*When you copy the swap image to the
alpha channel, it is converted to grayscale.
|
|
 Under
the Image menu, you will see the option to Store an image.
Generally since Howler is a dedicated painting application, you
work on one image at a time, however should you wish, you can
store an image or a number of images to access at a later time.
|
 Storing
an image puts it into it's own window that can be minimized for
later use. To restore it later, all you have to do is click on the
thumbnail.
|
|
Storing an image has many other options in addition to just
restoring a previous copy. You could also use several combine
modes to combine your images in interesting ways. You could just
restore the alpha channel (selection) that was associated with the
stored image. You can convert the stored image into a brush, or
copy it to the swap image, or you can use one of several different
color channels from the stored image.
|
By clicking on the Functions button, you get a menu of options.
Replace image replaces the current image with the one that was
stored. If your image has changed size since the stored image was
stored, it will be cropped into the new size.
The combine menu lets you combine the stored image with the
current image in a number of different ways.
Replace alpha replaces the current alpha with the one that was
stored with the image.
Use image as alpha converts the stored image to a grayscale
image and uses it as the alpha channel.
Replace existing image replaces the current image with the
stored image, obliterating whatever you are working on. If needed,
the image will be resized.
RGB Channels copies any of the Red green or blue channels of
the stored image into the main image. Say you only wanted to work
with one channel, you could store your image, clear your main
image and get just the one channel you wanted to work on. When you
are done, you can add in the other two channels.
HSV Channels converts the stored image to HSV space and copies
any of the Hue, saturation, or Value channel into the main image
as a grayscale image.
YUV Channels converts the stored image to YUV space and copies
any of the YUV channels into the main image as a grayscale image.
|
|
Working with Red, Green, and Blue channels independently,
using a stored image.
 As
an example, this image was cleaned up extensively by modifying
only the blue channel, which contained most of the film grain in
the image. 
The process was to store the original image and clear the image
to black. The blue channel was then added back, and a median
filter was applied to it several times to reduce the grain. Then
the red and green channels were added back to the image.
|
|
There are several transformation options available from the
Image menu. (It's worth noting that all of them also work on
entire animations)
Flipping an imagae creates a
mirror image.
In the examples, the image is flipped on the
horizontal axis, and on the vertical axis.
Rotating an image tilts the
image, like turning a photograph sideways by 90 degrees.
|
Original
image
|
Flip
x
|
|
Rotate
Clockwise
|
Flip
y
|
|
Re-sampling
Re-sampling, or scaling an image changes the size of the image
by stretching it to fit a new size, reducing or adding new pixels
as needed. The algorithm used to re-sample the image determines
its final quality. While an image with more pixels is generally of
higher quality, often large images need to be reduced in size for
various reasons, such as memory requirements.
|
The list on the left of the panel lets you select from a number
of preset sizes. These are image formats often used in the
field of video production. It is possible to edit this list.
See the section on preferences for more information.
If you do not want to use one of the preset sizes, you can
enter your own image size in pixels into the text boxes on the
right.
The Constrain check box forces your new size to match the same
aspect ratio as the original image.
The drop-down control
lets you select the type of interpolation used to re-sample the
image. Since images are composed of a series of pixels, it is
necessary to interpolate them to get a smoother result.
The interpolation types are nearest neighbor, bi-linear,
bi-linear+, and bi-cubic+.
The "+" in bi-linear+ and
bi-cubic+ means that the image is also super-sampled, or multiple
samples are taken of every pixel when they are scaled, for a
better result. Bi-cubic often produces the best result, and is the
default setting. If working on a very large megapixel image, it
may be required to use of the other methods, as Bi-cubic is
sensitive to overruns on very long lines of pixels.
The flip button
controls the orientation of the image by flipping the width and
height.
The Other units button
allows you to enter units other than pixels, such as inches or
metric units.
|
|
Resizing
 You
can change the image size without scaling the image. This results
either in the image being cropped, or in new areas being revealed.
|
The area at the top shows you the size of your original image,
and the middle section lets you set the new size, in pixels.
The Anchor lets you specify where in the new image that the old
image should be placed.
|
|
 Say
you wanted to make some room to add some text to the top of a
picture. You could add 100 pixels to the height of the image, and
change the anchor so the image would keep to the bottom.
The new area will be filled with the secondary color
|
|
Crop to Selection
 You
can crop an image to keep only the part that interests you.
This is like chopping off parts of a photograph with scissors.
To do so, 'select' the area you want to keep with an alpha
channel tool, like the Rectangle to alpha tool on the tool panel.
Use it to create a marquis (marching ants) around the area.
Select 'Crop to selection' from the Image menu, and your image
will be cropped.
Result of cropping.
See the section on the Alpha
channel for more information on selections.
|
The Crop tool
 You
can also use the crop tool to interactively select the area you
want to crop, including removing rotation and skew from the image
before cropping.
The
corners of the crop tool allow you to scale the area to be
cropped.
The
circular control on the crop tool allows the tool to rotate to
correct for rotation in your image.
The
parallelogram control on the crop tool allows you to correct for
shear (for example, an inexpensive digital camera may capture a
moving image slowly enough that motion is captured as a top-down
shearing effect.
|
|
Make an image seamless
Sometimes you want to make an image
or texture seamless. This can be useful for game textures or image
maps for a 3d object. It can also be useful for creating terrain
images for the Puppy Ray ray-tracer. No matter what the use, it
can be very easy to accomplish with the “Make seamless”
command under the image menu.
|
 Here,
the Seamless filter is used to create a “tileable”
noise pattern (generated with the plasma noise filter.)
The filter trims part of the left
and bottom of the image, and blends them with the top and right
part of the image. The trim amount can be set for both horizontal
and vertical directions separately.
An option button allows you to
apply the filter either to the current image, or the current
brush. The seamless feature on the Image menu is, in fact, the
same one found on the brush menu, but with this option checked,
depending on if it was started from the Image menu or the Brush
menu.
The “Keep original size”
checkbox, if checked, causes the image to be enlarged to fit the
original size of the image, to account for the amount that has
been trimmed off to blend the edges.
|
|
The next few features act like filters
to change the appearance of the image . The difference between the
features on the image menu, and the ones under the Filter menu is
that here, the alpha channel is ignored, and the way the feature
handles animation is somewhat different.
|
|
Grayscale
  
|
The Grayscale menu item converts a color image into a greyscale
image. Two modes are Average, and Video weighted,
while a third allows exposing
the grayscale image as if through a colored lens to create unique
effects.
In the first case, the red, green, and blue channels are
mathematically averaged with the formula (R+G+B)/3
With Video weighting averaging, the channels are averaged in a
way that is more consistent with human vision and video systems.
The formula is 0.299 * red + 0.587 * green + 0.114 * blue.
|
|
Exposing a grayscale image through a lens
Below, the same color image is
converted to 2 different grayscale images, each with a very
different look and feel.
 Here,
a grayscale image is created by “exposing” the color
image through a blue lens, greatly deepening the blue sky in the
image.
|
 Here,
a grayscale image is created by “exposing” the color
image through a yellow lens, greatly brightening the blue sky in
the image.
|
|
Inverting an image
|
Inverting an image creates a negative image, like you may or
may not remember from the old days of film cameras.
|
|
Expanding dynamic
range
 
Expanding dynamic range is a quick way to automatically adjust
the contrast of an image.
|
Dynamic range refers to the ratio of the highest (lightest) ,to
the lowest (darkest) intensity or value in an image.
In a 24 bit image, with 8 bit per channel, the highest value
for any channel is 255, and the lowest value is 0. If the value
for a pixel in all three channels is 0, then the color is black.
If all the value for all channels is 255, then the color is white.
However, not all imaging devices capture perfect blacks or
whites, and may give you an image that looks muddy. Expanding the
dynamic range can often make these images look nice.
|
A histogram shows the effects of expanding dynamic range.
The closer the range of values is to the edges of the histogram,
the more contrast your image will have.
|
|
Very similar to the idea of Layer Mixing, is Swap Mixing. In
fact, they are part of the same sub-system, but swap mixing has
its own uses if you only want to work with your main and swap
image.
|
See the section on Layer Mixing to
learn more.
|
|
 Swap
mixing options can be accessed by right clicking the icon on the
top, right corner of the tool panel, under the previews tab. (They
are also available on the Layer mixing panel.
*Swap mixing is very similar to layer mixing
|
Swap mixing activates swap mixing. Your main image will be
mixed with the swap image visibly in real-time as you work. The
images remain separate, but you can see the results of them being
combined on screen.
Swap images (buffers) swaps the main
and swap images. It’s the same as pressing the ‘j’
key.
Merge with swap causes the two images to be merged
using the current mixing mode. See below for an explanation of the
mixing modes
Open layers panel opens the layers panel should you need it.
Set current layers mode lets you change the current layer's
mode, or in this case, the mode for the swap mixing. If you where
working with layers, you could change the current layers mode.
Set tracing paper opacity lets you change the opacity of the
tracing paper mixing mode.
Show alpha causes the image thumbnail to represent the alpha
channel.
Note Layers are not saved with a file, so you will
have to merge your layers before saving your image.
|
|
 With
this sub-menu, you can set the current mode for swap mixing.
|
Default mode is Multiply mode.
Additive Adds the RGB values of the main and swap
images
Subtractive subtracts the main image from the swap
image.
Multiply mode multiplies the pixels of the swap and
main images (and divides them by 255.) The result is similar to
painting with ink on ink. The result is always darker.
Divide
is the complement of multiply. Use it as you see fit.
Screen
is similar to additive but keeps an image from ‘blowing out’
or becoming overly bright. It’s often useful for effects
like stars and fire.
Around gray combines two colors around
their middle brightness level.
Tracing paper lets the swap
image show through, a lot like tracing paper.
|
|
One way that the swap image is useful;
you can use the swap image to displace your main image. See the
section on Displacement filters for more information
  
|
|
Clearing
an image from the Image menu clears it to the secondary color.
If
you want to fill your image to a specific value, or if you want to
fill using any of the Fill tools, then you can use the Fill item
under the Image menu. It fills the image, or your current
selection using the current fill mode. This mode can be a plain
color, a gradient, a pattern from a custom brush, or a number of
other effect. See the section on Fill tools for more
information.
Paint
fill is a special tool that fills the image or selection with
a paint like effect. The values in the alpha channel have an
impact on the result of the paint fill.
Adjustable
paint fill goes a step further and lets you adjust the effects
orientation with a rubber band control.
The effect is also heavily effected by your current opacity.
