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Distort filters

Blinds

This Plug-in makes blinds. It's like slicing your picture in shreds and pasting the slices to the different sections of the blind.

To enable a transparent background, you have to work in layers or add an Alpha channel to the background, otherwise you'll end up with the background color in the toolbox.

You can create both vertical and horizontal blinds, just check the right button. Displacement refers to the open angle of the blind. A zero degree angle makes the blinds shut close and if you set it to 90, you'll open them as much as possible.

Curtain

This filter will make it look as if you are looking at your image through a curtain (and as it happens, this curtain already has your image printed on it!).

What happens when you apply this filter vertically, is that the image is copied, the copy is rotated 180 deg, thinly slashed and then combined with the original image. The same will happen if you choose Horizontal but from a horizontal perspective. You can also combine it so it will do both
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Emboss

Stamps or carves out a three-dimensional look to your image. Emboss only works for RGB images.

The direction of the stamp (inwards or outwards) is determined by the original brightness value, bright parts will look like they are raised, dark parts will look like they are carved.

Depth determines the embossed carve depth.

The Azimuth slide determines light direction, but so does Elevation. The most exact way to describe Azimuth is as "from which direction the sun rises in the morning". Think of Azimuth as a shining satellite, moving around your image - the light in the image will change as it moves. If we thought of Azimuth as the sun in the morning, you might think of Elevation as the "time of the day". Think of the sun when it reaches zenith. There will be no shadow. It's the same with Elevation, and if your depth is big, the lowest parts will look like black holes (quite good edge detect). When the sun falls or rises, the shadows will get longer or shorter, and the direction of the shadows will also change.

As you may have noticed, Emboss will make your image gray. Bumpmap keeps the color information, but the carving will not appear as deep as with Emboss. The images below have been embossed respectively bumpmapped with the same values, so you can see the difference. Emboss makes a surface look like metal or rock. Bumpmap just puts more depth to your image, like an impression on paper or leather
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Engrave

Turns your image into something which looks a lot like an etching. The slide More Height determines the depth of the engraving.You'll get more realistic etchings with low height values (close to 3). Limit line width is a limit in how many shades of gray you want. You will get more contrast if you don't check this button, and the etching will also get more realistic. On the other hand, you can get quite interesting results with this option.

IWarp

This is Gimp's answer to Kai's Power Goo. It's quite an amazing distort filter. You can grow, move, shrink, swirl or remove parts of an image. You can set the amount of distortion, and how large the deformation zone should be.

To create a distortion, you just drag the mouse in the preview image and you can watch the distortion take place. If you not are satisfied with a distortion, click reset and the image will be back to normal. Like in Power Goo, you can animate the distortions you've just made, and play it like a film.

Parameters

Let's take a look at what Warp can do for you.

• Deform Radius: This parameter sets how big/small the distortion area should be when you move the mouse over the preview. It refers to the radius (in pixels) from the centre of the mouse pointer.
• Deform Amount: Sets the amount of deformation in a scale from 0.00 to 1.00.
• Move: Lets you stretch parts of the picture. You can for example stretch a tiny little butt of a nose, and turn it into something a witch could be proud of.
• Grow: Grows a part of the image.
• Shrink: Shrinks a part of your image.
• Swirl: Lets you twist a part of the image, either clockwise or counter clockwise
• Remove: Will remove a distortion as a whole, or just partly. This is the perfect tool for adjusting a distortion, i.e you don't have to press reset if you failed to do what you wanted to do (If you are making a animation this correction will appear in one of your frames).
• Reset: Simply resets the image to the original state.
• Bilinear: If checked, warping will get more smooth.
• Adaptive Supersampling: (see the blend tool).
  

Animation: By checking the Animate button, you will get a layered image, ready for making GIF animations. You can set the number of frames, and in what order you want to play the frames of the film.

• Normal mode: The first frame is the original image, and the following frames are gradually distorted until the last frame, which displays the fully distorted image you made in the preview window.
• Reverse is the opposite of Normal.
• Ping Pong: Creates a frame sequence like this: original image..... distorted image... original image
• Reverse and Ping Pong: distorted image..... original image.... distorted image.
• With reverse and reverse ping pong, you must remove the background layer after you have applied the filter to make it work properly.
  

Page curl

With this plug-in, you can curl, or lift any corner of your image. To use Page Curl, you must have at least one layer and a background in your image. The top layer to curl and a bottom layer to curl against. The color of the back of the curled page is controlled by the current colors in the toolbox. The foreground color represents highlight, or the middle part of the gradient, and the background color represents shadow, or the first and last part of the gradient. You can also put a Shade under the curl, and set the Opacity of the curled page.

If you just want to curl a small part of the image, make a selection and curl the selection. This allows you to make a small curl, just as if the glue didn't stick properly to that corner of the image..

Polar Coords

The main achievement of this plug-in is to make circular or rectangular shapes of your image or drawable.

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Examples

To create a powerful, but rather unsophisticated text curve, you can apply this plug-in to a text string. You can also make a target circle out of some lines, or you can make rectangles out of straight lines.

• The slide Circle depth in percent controls how round your circle will be. A higher value will make it more circular (Pic 2), a lower value makes it more rectangular (Pic 3).
• The Offset angle controls where your circle/half-circle will start (in degrees) (pict4)
• The button Map from top controls if the bottom part (Pic 5) of the image turns up in the middle or not. Press this button and it ends up in the middle (Pic 6), unchecked will put it in the outer regions (Pic 7).
• Map backwards? controls whether the image will be mirrored or not.
• Polar to rectangular? lets you decide whether the image should be mapped to circular or rectangular. Press this button and it will map to rectangular (Pic 8)
  

Ripple

This plug-in displaces the image or selection in waves or ripples so that it looks like a disturbed water surface. You can displace the image in Sine or Sawtooth wave form. You can also specify the Period and Amplitude of the wave. Wrap, Smear and Black have the same functions as in the Displace plug-in, see chapter 32. If you unchecked antialiasing you will get rough edges. Note that you can ripple both horizontally and vertically.

Shift

This filter creates a random displacement of each pixel row, horizontally or vertically. Shift Amount determines how much a row should be displaced. You can't predict if it will displace left or right / up or down. You just know the amount of displacement.

Twist

The Twist is a plug-in which provides a variety of geometric image distortion functions. The principle of all distortion types provided by the Twist is to map the input image to the output image by translating the original pixels according to a 2D vector field which is determined by the selected distortion function. In order to support the user's creativity, some parameters (up to eight, depending on the function type selected) can be adjusted, resulting in different effects. The output of the Twist plug-in is a geometrically distorted image. The effect of a selected parameter setting can be viewed interactively in a preview image. Each selectable function provides eight predefined effects which can help the unexperienced to get a feeling for the parameter settings. Currently eight different distortion functions are available.

To use it, simply bring it up from the menu. Note that you cannot distort indexed images. If you have such an image, it must be converted to an RGB or grayvalue image.

There are four frames, the 'Preview image' frame, the 'Parameter settings' frame, the 'Functions/Effects' frame and the 'Cutoff function' frame.

Functions Effects

The first frame you'll probably want to use is the Functions/Effects frame. This frame contains two menus, the Functions menu and the Effects menu. You can choose one of several distortion functions by activating the Functions menu. Having chosen a distortion function you must choose a parameter set that, in combination with the chosen distortion function, defines the effect you will obtain.

There are two ways to define a parameter set. The first, and easier way is to select one of eight effects from the Effects menu in the Functions/Effects frame. The parameters defining the effect will be displayed in the Parameter settings frame. The effect on the image can be seen almost immediately in the preview image at the top left corner of the dialog window.

Parameter settings

The second way for choosing a parameter set is to use the sliders in the Parameter settings frame. Note that some of the sliders may be labeled 'unused', indicating that modifying this parameter will not affect the image distortion effect. The labels of the sliders depend on the distortion function.

In order to acquire a certain feeling for the parameters of each distortion function I recommend that you experiment with the sliders after having chosen an effect. If you feel that the preview image is too small to see what actually will happen to the image, do not hesitate to execute the Twist by pressing the [OK] button at the bottom of the dialog. The Twist will remember all parameters you have selected when it is started again providing you with the possibility of fine-tuning an effect.

The last frame, which has not been discussed yet, is the Cutoff function frame. The cutoff function is a mechanism for damping the image distortion function depending on the distance r from the image's center. This means that, when the cutoff function is activated, the image distortion is a product of the selected distortion function and of the cutoff function. The toggle button labeled Use cutoff is used for switching this modifier on and off. The meanings of the two parameters, r and dr, which can be modified by the sliders are visualized by figure 2 below. Note that some of the predefined effects use the cutoff function. So have an eye on this frame when you want to figure out which parameters yield an effect that you like.

Documentation by Peter Uray

Value Propagate

This plug-in works by spreading and increasing certain value ranges in a specified direction. The first two parameters, More White and More Black, have a large impact on scanned photographs (see pictures). You might describe the effect as a swelling of bright (respectively dark) areas where contrast is high, expanding at the cost of the opposite brightness value. When you run the filter several times, those areas will clog together in large square clusters, while middle values will remain relatively unaffected. The result is often quite artistic. The More White effect resembles oil painting, and More Black looks like watercolor. This filter is also very good for drawings. A black and white line drawing made in the computer will look more like a real ink pen drawing if you apply some More White to it, More Black will just thicken the line
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Tips

The next few parameters work best with drawings and computer made images with distinct edges. Scanned photos are either hardly affected, or the result is strange and unpredictable.

Foreground to Peaks draws a fine contour (with the current FG color) around defined objects or shapes in the image, and that includes Propagate cluster formations. If the object border is fuzzy, the FG outline starts where the object color fades out.

Middle Value to Peaks creates (if there isn't one) and propagates the transitional color (blend of object's edge color and background color) and blurs the image. It will blur more for every time you use it, because then the transitional color will be created from the new edge color.

Only Foreground propagates areas which match the exact shade of the foreground color in the toolbox, so soft and fuzzy edges don't propagate well with this option.

Only Background does the same, but for the background color. Sometimes these options causes pixels of the chosen color to spread in an asymmetric way - large lumps or clusters grow. This can occur when you spread soft brush lines, or when you run this filter several times. Don't worry about it - it's just the way this filter operates.

More Opaque/More Transparent only applies for images with an Alpha Channel (a layer or an alpha enabled background). Those options work exactly the same way as More White/Black, but white is replaced with opaque and black with transparent.

Value range can be set differently if you only wish to propagate areas in a certain range, like only very dark areas or only middle values. You can also set the Propagate Rate (amount) and the direction of the spreading. The check buttons Propagate Alpha respectively Value Channel can be used a locking device, if you're afraid to press the wrong button. (Note, this filter does not work for the kind of Alpha Channels you create in the Channels tab folder).

Waves

This plug-in is really nice. It simulates the effect that you get when you throw a stone in a pond (if you have unchecked the reflective button).

The amplitude is the height of your waves. Phase is where you are in your wave (it's like a sinus wave and the phase is where you are in that sinus wave).

Wavelength is how long your (sinus)wave is. The modes Smear and Blacken have the same function as in the displace plug-in, see chapter 32. If you check the Reflective button you will not get the simple "throw stone" effect, instead your wave will create an interference pattern.

Whirl and Pinch

This plug-in will distort your image in a centre circular way. Whirling distorts it much like the little whirlpool that appears when you empty your bath.

Pinch can be compared to applying your image to a soft rubber surface and pressing it in different ways. If the pinch slide bar has a negative value, it will look as if someone had tried to push a round object up toward you from behind the rubber skin. If you use a positive value, it looks like someone drags or sucks in the surface from behind, and away from you.

The slidebar for Whirl controls how many degrees you want to turn your image. The Pinch slide bar controls the type and amount of pinch.

Radius determines how much of your image will be affected. If you set radius to "2", the whole image will be affected. If you set the radius to "1", half the image will be affected, and if it is zero nothing will be affected (just think of it as the radius in a circle. 0 in the center and 1 halfway out...). To create a really realistic whirlpool, combine the two distort methods