Mask

A mask is a black and white image associated with a base image of the same size in pixels. You can think of it as a semi-transparent overlay that exactly covers the base image. Areas where the mask is white are selected while areas where the mask is black are not -- areas where the mask is gray are partially selected. Masks are used to restrict the operation of transformations and tools to the selected areas of the base image, for example to lighten or darken just part of an image.

Masks are created via Amount Controls. The amount control associates a mask with an image and determines how the mask is used.

Mask Dialog

While any black and white image of the correct size can be used as a mask, the normal way to create a mask is with the mask dialog which incorporates specialized masking tools.

To create a mask dialog, click on the square at the right end of an Amount Control and select New Mask... or select a mask from the list of images below in the menu.

If you close the mask dialog, you can re-open it by clicking on the square in the Amount Control and selecting Re-open Mask Dialog Box from the menu. To clear the mask, select Reset. To invert the mask (make white areas black and black areas white, select Reverse).

Mask dialog box:

The mask dialog box can be resized by dragging its edges or corners. Depending on the mask tool you are using, this can make it easier to adjust some of the curves or sliders.

As long as the mask dialog box is the current window, the current mask is displayed as a colored overlay on the input image for the transformation or tool. You can change the color and transparency of this overlay from the mask dialog. Clicking on the transformation or tool dialog box temporarily removes the overlay so you can see the input image underneath. Clicking back on the mask dialog box restores the overlay so you can see what parts of the image are masked.

Masks may be created in a single operation or as a sequence of operations. Each new operation creates a new mask which is combined with the current mask according to the mask mode (see below). Depending on the mode you select, you can add to an existing mask, trim it back, or mask just the areas masked in both the current and the new mask. If you create a mask in more than one operation, you can undo or redo operations.

Undo/Redo

The undo tool bar lets you undo or redo mask operations, one at a time.

If the undo or redo button is grayed, it means there are no operations left to undo or redo. If you undo too many operations by accident, you can click the redo button until you get back to where you wanted to be. However, once perform a new mask operation, you can no longer redo past that point.

You can use the keyboard shortcuts Ctrl-Z for undo and Ctrl-Y for redo.

Note: When using Undo with any mask tool that has an Apply button, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

Set Mask

The set mask tool bar provides shortcuts for some simple masking operations.

 -- Makes the mask all white.

 -- Makes the mask all black.

 -- Makes the mask all mid-level gray.

 -- Inverts the current mask.

 -- Makes the left half of the mask white and the right half black.

 -- Makes the right half of the mask white and the left half black.

 -- Makes the top half of the mask white and the bottom half black.

 -- Makes the bottom half of the mask white and the top half black.

All the above buttons except Invert replace the current mask entirely, but they do not clear the list of mask operations. This means that if you Undo any of these operations you get back the previous masks. This can be useful if you want to temporarily reset the mask and then restore it, but it means that when you edit the mask or save it as part of a script, all the previous operations will be repeated even though their end result is ultimately discarded. To clear out the mask operation list, use the Reset command from the Mask Settings Menu instead -- this sets the mask to all black, you can then alter it if necessary using the Set Mask buttons above.

Mask Mode

The mask mode tool bar controls how the current mask will be modified by the next mask operation you perform.

 -- Adds the new mask to the current mask. Use this mode to create or extend the currently masked region.

 -- Subtracts the new mask from the current mask. Use this mode to trim a masked region.

 -- Clears the parts of the current mask that do not overlap the new mask. Use this mode when you want to create a mask based on two conditions being met simultaneously, for example, to create a mask consisting of all pixels in a certain region with colors in a certain range.

 -- Inverts the current mask where new mask data is present. Use this mode to reverse part of a mask.

Mask Overlay Color

Masks are displayed as an overlay on the base image when the mask dialog is the active window. Set the color of the mask overlay to red, blue, green, or white by clicking the button of the corresponding color on the tool bar at the top of the screen. This setting is global so changing it affects all other masks as well.

Mask Transparency

The mask transparency tool bar at the top of the screen determines if and how the mask overlay is displayed. This setting is global so changing it affects all other masks as well.

 -- Mask is totally transparent – base image is fully visible. This setting is best when you are adjusting transformation parameters and want to see the result image without the mask overlay.

 -- Mask is 75% transparent – base image is mostly visible

 -- Mask is 50% transparent – base image is somewhat visible. The semi-transparent settings are useful for visualizing the relationship between the mask and the base image.

 -- Mask is totally opaque – base image is obscured where the mask is white. This setting is best when you want to see what parts of the base image are masked.

 -- Only mask is displayed – base image is hidden. This setting gives you a detailed view of the mask which can reveal subtle variations you might miss when the mask is viewed over the base image.

Mask Tools

The main mask tool bar is where you choose the masking tool you want to use next.

 -- Freehand Tool.

Click on the base image and, holding the mouse button down, outline of the region you want to mask. When you release the mouse button, the endpoint of the outline is automatically connected to its starting point and the interior of the outlined region becomes the new mask. This new mask is then combined with the current mask according to the current mask mode.

 -- Rectangle Tool.

Click on one corner of a rectangle in the input image and, holding the mouse button down, move the cursor to the diagonally opposite corner. When you release the mouse button, the rectangle you have selected is outlined. You can click and drag the sides, corners, or interior of the rectangle to reposition it if necessary. To create a square region, hold down the Shift key while dragging the sides or corners of the rectangle.

When you click Apply, the selected rectangle is combined with the current mask according to the current mask mode.

Note: When using Undo with the Rectangle mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Oval Tool.

Click on one corner of a rectangle in the input image and, holding the mouse button down, move the cursor to the diagonally opposite corner. When you release the mouse button, an oval filling the rectangle you have selected is outlined. You can click and drag the sides, corners, or interior of the rectangle to reposition it if necessary. To create a circular region, hold down the Shift key while dragging the sides or corners of the rectangle.

When you click Apply, the selected oval is combined with the current mask according to the current mask mode.

Note: When using Undo with the Oval mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Polygon Tool.

Click on one corner of a rectangle in the input image and, holding the mouse button down, move the cursor to the diagonally opposite corner. When you release the mouse button, the rectangle you have selected is outlined. A second rectangle is also displayed just outside the mask rectangle – this outer rectangle is used to enlarge or shrink the entire polygon.

Once you have created the initial rectangle, you can modify it by adding or removing vertices. To add a new vertex, shift-click (while holding down either Shift key, position the cursor and click once with the left mouse button) near the side of the polygon connecting the two vertices you want to insert between. To remove a vertex, control-click (while holding down the Ctrl key, click once with the left mouse button) on it. There must always be at least three vertices to define a polygon. To reposition a vertex, simply click and drag it; to reposition the entire polygon, click and drag the handle displayed at the center of the polygon. To resize the entire polygon, click and drag on one of the sides or vertices of the rectangle that surrounds the polygon.

When you click Apply, the selected polygon is combined with the current mask according to the current mask mode.

When you click Save..., you are prompted to select a pathname; when you click Save, the current polygon settings are saved in the file you select.

When you click Load..., you are prompted to select a pathname; when you click Open, the current polygon settings are replaced by those from the file you select. This lets you restore a saved polygonal shape for use as a mask.

Note: When using Undo with the Polygon mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Spline Tool.

A spline is a smooth curve that passes through a specified set of control points.

Click on one corner of a region in the input image and, holding the mouse button down, move the cursor to the diagonally opposite corner. When you release the mouse button, the region you have selected is outlined. A rectangle is also displayed just outside the masked region – this outer rectangle is used to enlarge or shrink the entire region. Once you have created the initial region, you can modify it by adding or removing control points. To add a new control point, shift-click (while holding down either Shift key, position the cursor and click once with the left mouse button) near the line segment connecting the two control points you want to insert between. To remove a control point, control-click (while holding down the Ctrl key, click once with the left mouse button) on it. There must always be at least four control points to define a region. To reposition a control point, simply click and drag it; to reposition the entire region, click and drag the handle displayed at the center of the region. To resize the entire region, click and drag on one of the sides or vertices of the rectangle that surrounds the region.

When you click Apply, the selected region is combined with the current mask according to the current mask mode.

When you click Save..., you are prompted to select a pathname; when you click Save, the current spline settings are saved in the file you select.

When you click Load..., you are prompted to select a pathname; when you click Open, the current spline settings are replaced by those from the file you select. This lets you restore a saved shape for use as a mask.

Note: When using Undo with the Spline mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Feather Tool

Masks such as those created by the freehand, polygon or spline tools are anti-aliased to removed jagged edges, but the edges are still sharp. Feathering is used to soften the edges of a mask or to expand or shrink the masked region. Using feathered masks when compositing images makes the result look more natural and less like you just cut one image out with a pair of scissors and glued it on top of the other one.

Feather Width

Feather width specifies the distance in pixels that mask edges will be extended. Positive values extend the current mask outward making the masked region larger. Negative values shrink the current mask inward making the masked region smaller.

Falloff

Linear and Cosine falloff soften the edge of a mask by causing it to fade gradually across the feather width, either with a linear fade or an S-shaped fade. Step falloff grows or shrinks a mask by extending it inward or outward by the feather width without softening its edges.

Corners

Round extends mask edges in a circle; Square corners extends mask edges in a square.

Click Apply to feather the current mask.

Note: When using Undo with the Feather mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Blur Tool

Blurring can be used like feathering to soften the edges of a mask although, unlike feathering, it blurs both sides of the edge. Large radius values are useful creating dodging and burning masks.

Radius

The radius setting specifies the amount of blurring; the larger the radius the more the mask will be blurred.

Click Apply to blur the current mask.

Note: When using Undo with the Blur mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Color Range Tool

The color range tool lets you create a new mask based on a range of colors in the base image.

You can set Color Space to RGB, HSV, or HSL. Depending on the color space you select, the three color bars are labeled accordingly – one for each channel. If the input image is black and white, then there is only a single bar for gray level.

Each color component has two pairs of sliders, one white and one black. The white sliders adjust the range of values for that channel that are fully selected; the black sliders control how quickly the selection falls off for values outside the white range. The gray scale below the color stripes illustrates the extent to which colors will be selected for each color channel. Where the scale is white, pixels with those values will be fully selected; where the scale is black, pixels will be deselected; where the scale is gray, pixels will be partially selected.

Tic marks indicate the values of the three color channels for pixels in the input image. As you move the cursor over the input image with the mouse button down, these markers are continuously updated to correspond to the color of the base image at the cursor location. The color bars reflect how this probe color varies as you change one channel leaving the other two fixed. In the example above, the H (Hue) bar shows that an orange pixel has been selected and shows how the color changes as the hue component is varied. Similarly, for the saturation and value components.

When you click Apply, a new mask is computed as the set of pixels in the input image that fall within the ranges you have specified. This new mask is then combined with the current mask according to the current mask mode.

When you click Contract, Picture Window shrinks the ranges down to just include the color indicated by the three tic marks. As you move the cursor over the input image, holding down the shift key and depressing the left mouse button, the current ranges are automatically expanded just enough to include the colors the cursor is passing over. This technique is a convenient way to set the range values to include all the pixels in some part of the image.

Note: When using Undo with the Color Range mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Paint Tool

Click on the input image and move the cursor with the left button down to paint on the mask.

The Radius, Transparency, Softness, and Spacing sliders adjust the characteristics of the. A representation of the brush radius, transparency and softness is displayed at the bottom left of the Mask Dialog. Depending on the current mask mode, painting can add to or subtract from the current mask.

The Apply To control lets you modify the way the paint tool works:

All Pixels -- the paint tool works normally.

Pixels in Color Range -- only paints areas in the currently selected color range as specified by the Color Range tool (see above). To change the color range settings, switch to the Color Range tool and then back to the Paint tool.

Similar Pixels (Fixed) -- samples the color of a small area of the underlying image at the cursor location at the start of each brush stroke to establish a base color. For the remainder of the brush stroke, only pixels whose color is close to the base color are masked when the brush is applied. A Threshold slider is displayed just below the Spacing slider to let you adjust how closely other pixels must match the base color to be masked. The smaller the threshold value, the more closely pixels must match the base color for the brush to be applied.

Similar Pixels (Track) -- like Similar Pixels (Fixed) except the base color is resampled each time you move the cursor. This helps you mask around the edge of an object even if the background color is varying.

 The Overlapping Strokes control lets you change what happens when you paint over the same area more than once:

Accumulate -- painting over an area repeatedly keeps adding to the mask, making it less and less transparent

Don’t Accumulate -- painting over an area repeatedly never paints beyond the brush transparency

Stylus Pressure -- If you are using a pressure-sensitive stylus, this control lets you determine the effect, if any, that stylus pressure has on the current brush stroke. If you are not using a tablet, this control is set to Ignore and the other options are grayed out.

Ignore -- stylus pressure has no effect.

Controls Opacity -- increasing stylus pressure reduces transparency, making the stroke more opaque.

Controls Radius -- increasing stylus pressure increases the brush radius, making it larger.

Controls Hardness -- increasing styles pressure reduces softness, making the edges of the brush harder.

Controls Flow -- increasing stylus pressure reduces spacing, causing the brush to be applied more often as you move the stylus.

 -- Curve Tool

This tool lets you select regions of an image based on their brightness, saturation or color.

The Channel control lets you select which channel to base the mask on. This control is only present if the base image is color – for black and white images, the curve is always based on the image brightness. For more information on color channels, see Color Spaces. The available color channels are:

Luminance -- luminance

R -- red

G -- green

B -- blue

HSV V -- HSV brightness

HSL L -- HSL brightness

HSV S -- HSV saturation

HSL S -- HSL saturation

HSV H -- HSV hue

HSL H -- HSL hue

The curve control at the bottom of the dialog box lets you select what part of the tonal range of the image to select. To higher the curve value for a given brightness level, the more it will be selected in the mask. The curve illustrated above creates a mask that fully selects black pixels and gradually trails off to mid-tone and brighter pixels.

When you click Apply, the selected mask image becomes the new mask. This new mask is then combined with the current mask according to the current mask mode.

Note: When using Undo with the Curve mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Flood Fill Tool

This tool lets you select connected regions of an image of a similar color. To use the flood fill tool (sometimes called a magic wand in other programs), just click on the input image. All pixels surrounding the one you click on that within the threshold of the same color will automatically be combined with the mask according to the current combine mode. Only pixels that are directly connected to the one you click on will be selected however so the selected region will stop growing once it is surrounded by dissimilar pixels, even if there are colors elsewhere that match.

Threshold

The threshold setting specifies how closely pixels must match the pixel you click on to be included in the selection. A threshold of 0.0 requires an exact match; larger thresholds loosen the matching criterion.

 -- Separate Tool

The separate tool creates a new mask based on two or more colors you select -- at least one black color and at least one white color. It does this by computing the relative amounts of each color that, when blended, most closely approximate each pixel in the underlying image. Where the image is best approximated by one of the black colors, the mask is black – where the image is best approximated by one of the white colors, the mask is white. Where the best approximation is a mixture of the two colors, the mask is an intermediate gray. The result is a mask that separates image elements based on their similarity to the black and white colors.

This tool can be used, for example, to separate a complex tree line from the sky by choosing as two colors: a color from the trees just below the tree line and a color from the sky just above the tree line. Once you select the two colors, click the Apply button to create the new mask. The big advantage of this technique is that it automatically accurately feathers the mask at the boundary. Finding the two colors that best separate the image elements may take some trial and error. As a rule, the more similar the black and white colors are to each other, the more complete the separation will be. The farther apart they get, the more intermediate grays the mask will contain. In the case where the sky has more than one color or the trees have more than one color, you can assign additional black or white colors.

If the black and white colors are identical, the separate tool makes the mask pure black where the image is darker then the black and white colors and pure white where it is lighter.

Black/White Colors

There are two rows of four color patches each. The top row are the white colors and the bottom row are the black colors. The first patch in each row is always enabled since at least one black and one white color is required for the separate tool to operate.

To make an enabled patch current, click on it. The current patch is marked with a white outline.

To set the color of the current patch, click on a part of the input image that has the color you want to select.

To enable a disabled patch or disable and enabled patch, double click on it. The first black and the first white patch cannot be disabled.

If the input image is black and white, only the luminance of the selected color is used. As a shortcut, you can set the black color by clicking on the input image.

Apply

When you click the Apply button, the new mask is created and combined with the current mask according to the current mask mode. For each pixel in the base image, the closest black and white colors are used to create the mask by determining what mix of the black and white colors best matches the base image.

Note: When using Separate with the Rectangle mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Texture Tool

This tool lets you select the parts of an image with a given texture, where texture is defined as the amount of variation among pixels in a given area. Variation can be measured in several different ways. This tool can be used to create a mask that isolates edges or other areas of large local variation in an image. Such masks are often used in conjunction with blurring or sharpening to restrict them to smooth or rough areas.

Method

The method setting lets you choose among three different ways of computing texture. The Max Difference setting computes texture as the largest difference between the central pixel and all the other pixels in its neighborhood. The Average Difference setting computes texture as the average difference between the central pixel and all the other pixels in its neighborhood. The Difference from Average setting computes texture as the difference between the central pixel and average of all the other pixels in its neighborhood. These three methods generally produce similar results with Max Difference producing the most pronounced effects and Difference from Average producing the most subtle effect.

Neighborhood Size

The neighborhood size may be selected as 3x3, 5x5, or 7x7. This selects how large an area around each pixel is considered to be its neighborhood. Smaller values are better at picking up fine detail, but larger values may work better for softer images.

Histogram Display with Black and White Sliders

The histogram display shows you how common different texture values are over the entire image. Values near the left indicate how many pixels are in relatively smooth areas. Increasingly greater texture is generally less common except perhaps in very noisy images. By dragging the black marker to the right, you can exclude smooth-textured areas from the selection. Moving the white slider sets a progressive cutoff for higher textured pixels.

Note: When using Undo with the Texture mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Linear Gradient Tool

This tool lets you define a linear gradient using a Color Line control.

To specify where the endpoints of the gradient are located on the image, click and drag to draw a line on the image. You can move the endpoints or the entire line to reposition it if necessary. The gray levels on the color line are then used to create a gradient the runs from the beginning of the line you drew to the end. Areas past the beginning or end of the line have a constant gray level corresponding to the endpoint of the color line. Click Apply to create a gradient mask with is combined with the current mask according to the current mask mode.

You can save and load linear gradient settings via the Load... and Save... buttons. This saves the locations of the gradient endpoints and the contents of the color line control. The endpoint coordinates are scaled according to the width and height of the input image so if you reload the settings on an image of different size, the gradient is stretched to fit.

Note: When using Undo with the Linear Gradient mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Oval Gradient Tool

This tool lets you define an oval gradient using a Color Line control.

To specify where the location of the gradient, click and drag to draw a box on the image that contains the oval. You can move the endpoints, sides or the entire box to reposition it if necessary. The gray levels on the color line are then used to create a gradient the runs outward from the center of the oval you drew to the oval. Areas outside the oval have a constant gray level corresponding to the right endpoint of the color line. Click Apply to create a gradient mask with is combined with the current mask according to the current mask mode.

You can save and load oval gradient settings via the Load... and Save... buttons. This saves the locations of the gradient center and radius and the contents of the color line control. The center and radius coordinates are scaled according to the width and height of the input image so if you reload the settings on an image of different size, the gradient is stretched to fit.

Note: When using Undo with the Oval Gradient mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- PinholeTool

This tool lets you remove small white or black holes in a mask sometimes left behind by other mask tools. It scans the entire current mask looking for white or black specks that are different from the surrounding area by at least the threshold. A speck is defined as a connected region in the mask with no more than a given number of pixels all of which are within a given threshold of the central pixel. If any specks are found, they are replaced with the average of the mask values surrounding them.

Speck Size -- specks containing more than this number of pixels will be ignored

Threshold -- the maximum difference between a speck pixels. Smaller values will find more specks -- too small and everything looks like a speck, too large and nothing looks like a speck.

Remove -- lets you remove only light specks, only dark specks or both

Apply -- speck remove starts when you click this button.

Note: When using Undo with the Pinhole mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Median Filter Tool

This tool smooths the current mask by applying a median filter. Median filters reduce noise and tend to round off any sharp corners or fine detail, especially if applied at a large radius.

Radius -- the radius of the median filter. Larger values do more smoothing.

Threshold -- the median filter is only applied when it changes the mask by less than the threshold.

Apply -- median filtering starts when you click this button.

Note: When using Undo with the Median Filter mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

 -- Mask Brightness Curve Tool

This tool applies a brightness curve to the current mask to create a new mask. The most common use for this tool is to increase or decrease the separation between masked and unmasked areas.

The curve control at the bottom of the dialog box shows you a histogram of the current mask and lets you define a curve to apply to the mask.

When you click Apply, the curve is applied and the mask is updated. The current mask mode is ignored.

Note: When using Undo with the Mask Brightness Curve mask tool, the mask operation is reversed in two steps. The first Undo reverses the action of the Apply button and lets you edit the control points and re-apply the modifications. The second Undo reverses the mask operation.

Settings Menu

Save Settings As...

Selecting this option saves the entire sequence of operations used to create the current mask in a mask settings file. However, if the current mask was created from another image (by selecting the name of that image from the drop-down menu from clicking the white square in the Amount control), then the initial image is omitted from the mask settings file. The only way to save both a mask and the image(s) it depends on is to use a script  or workspace script file.

Load Settings...

Selecting this option restores a saved mask settings file, including the entire sequence of operations used to create the mask. However, if the current mask was created from another image (by selecting the name of that image from the drop-down menu from clicking the white square in the Amount control), then the initial image is omitted from the mask settings file. The only way to save both a mask and the image(s) it depends on is to use a script  or workspace script file.

Save As Default Settings

Selecting this option saves the current mask settings, but does not save any of the mask operations. These settings are then reloaded whenever the mask is reset or a new mask dialog box starts up.

Save mask as image file…

Selecting this option lets you save the current mask as an image file for later use. To use an image as a mask, it must have exactly the same width and height in pixels as the base image, so the saved mask can only be applied to other images of the same size.

Save current mask

Selecting this option internally stores a copy of the current mask for use in a subsequent step in creating a mask.

Combine saved mask

Selecting this option combines the saved mask (see above) with the current mask, according to the current masking mode (Add, Subtract, Overlap or Invert). This mechanism makes it possible to create complex masks that satisfy multiple conditions. For example, suppose you want to combine two masks, each of which take two steps to create. You create the first mask and save it using Save current mask (see above). Then create the second mask and combine the first one using Combine saved mask.

Compute Area...

Selecting this option causes Picture Window Pro to compute the area of the input image covered by the current mask. The result is reported both as a number of pixels and as a percentage of the total image area of the input image. Pixels that are partially masked are counted as fractions, so the pixel total may not be an integer.

Tips

If the mask overlay is missing...

Check the Mask Transparency tool bar to make sure you have not selected a transparent mask.

To check your progress...

In the process of creating a mask, you may find it useful to reverse the masked and unmasked regions with the Invert button to help visualize the masked region. Or you can toggle the Mask Transparency setting to turn the overlay on and off.

Sub-Pixel mask resolution

By zooming in on the base image window, you can adjust the location of the edge of the masked region by fractions of a pixel. This lets you make very fine adjustments when using the freehand, rectangle, oval, polygon, and spline tools as Picture Window records the location of each vertex or control point to sub-pixel accuracy and computes and anti-aliases the mask with great precision.

Work from rough to fine detail

To mask a complex region, start by making a crude mask of the entire region with the outline tool, then zoom in and refine the mask by adding or removing small amounts at a time around the edges.

Creating soft masks

Here is a quick way to create a soft-edged mask for dodging and burning or making similar adjustments that need to blend in smoothly.

First use the Freehand Outline tool to circle the region you want to mask, leaving extra room around the boundary. You don't have to be particularly accurate since the details of the edge of the region will be smoothed out.

Next use the Mask Blur tool to blur the mask - the larger the radius, the smoother the blend. The blur tool shrinks the masked region by the blur radius, so this is why you need to be generous when marking it with the freehand outline tool. If you over- or under-blurred, click the Undo button and try again.

The range tool

The range tool is very useful for creating a mask based on the color of a region of the input image.

Filling pinholes in a range mask

When you create a mask with the range tool, it may leave small pinholes unselected. You can fill these quickly by painting over them with the mask paint tool using an opaque, hard-edged brush.

Creating a mask that isolates shadow, mid-tone, or highlight areas

To create a mask that isolates the parts of an image with a certain range of gray levels, use HSV or HSL color space and use the white sliders to bracket the main part of the gray scale you want to select. Then pull the black sliders out to feather the effects of the mask over adjacent gray levels. You can use the resulting mask with various transformations to alter the color or brightness of the shadows, mid-tones, or highlights of an image.

Feathering

If you don't feather the edges of a mask, the boundary between the transformed and unmodified regions of the input image will often be disturbingly obvious. Feathering blends the effects of the transformation around the edges and creates a more natural result. The larger the feather radius, the more the edges of the mask are feathered.

For most transformations that adjust brightness and color of an image, gradual feathering that falls off out from the regions you are modifying usually creates the best results (4-10 pixel radius).

When using the composite transformation, a smaller feather radius (1 to 4 pixels) usually works better.

When using the blur transformation to remove grain from the sky without blurring the rest of the image, try using the range tool to select the sky region and then feather with a negative radius and sudden falloff to avoid blurring the horizon line or any foreground elements silhouetted against the sky.

To feather a mask more than is possible using the feathering tool, you can use the Blur tool with a large radius.