Xara Tutorial Feathering

Transcription

1 Xara Tutorial Feathering 1

2 Table of Contents 1 Introduction How to feather an object Vector feather Bitmap feather Uses of bitmap feathering Feathering versus Gaussian blurring Final comments

3 1 Introduction Feathering is a technique used in Xara to soften the edges of any object (including groups, bitmaps and even vector objects. It is a powerful feature that was pioneered by Xara when Xara X (version 1.0) was released back in January 2001 (Figure 1.1), and is still not currently present in many comparable graphics software. Figure 1.1. A screenshot showing the inception of vector feathering: Xara X1 (version 1.0) back in January Until vector feathering came along in Xara, a blend between a similar transparent object was typically used to simulate soft edges. This technique is still used today for specialised circumstances but feathering is more commonly applied. 3

4 In December 2005, Xara Xtreme 2.0 was released and introduced the Live Effect tool. Within this tool was a plug-in for bitmap feathering, which has particular uses for feathering bitmaps with an alpha channel, as discussed in section This tutorial discusses how to apply each type of feathering, and is discusses the distinction between them both with example. between feathering and Gaussian blurring. It also briefly discusses the difference Note 1: This.docx document has been written in MS Word 2007 in Print Layout View, and thus is printable. Furthermore, using the latest features of Xara, all images in the document were pasted from Xara, and thus are Xara objects; simply double clicking on them will load them directly back into Xara for easier, interactive inspection. Note 2: A document tree is available in Word to see the structure of the document and make navigation easier: In Word 2003 and below: go to View > Document Map. In Word 2007: go to View tab > check Document Map checkbox in Show/Hide palette. Note 3: This document also contains cross-references to key parts of the document. For example, Ctrl-clicking on text such as Figure 1.1 will cause the document to jump to the relevant location. Sections and figures references take advantage of this feature. 4

5 2 How to feather an object Any object can be feathered whether it be vector or bitmap or group of objects in Xara. There are two distinct types of feathering: vector and bitmap. Vector feathering is the most likely used of the two, and the distinction between them is slight but significant. Each will be addressed in the corresponding sub sections (section 2.1 and section 2.2 respectively). It should be noted that in versions of Xara between 1.0 and 3.2 inclusive, there is a 50 pixel feathering limit that can be applied to objects. This is apparently due to performance issues, as will be discussed later; however with processing power increasing, it s uncertain how long such a limit will remain. 2.1 Vector feather Vector feathering was pioneered by Xara and is the most commonly used type of feathering within Xara. Unlike bitmap feathering, vector feathering is truly resolution independent (this will be discussed shortly in section 2.2.1). It is extremely simple to feather an object in Xara. Simply select the object(s) and use the feathering slider on the standard toolbar, shown in Figure 2.1, to increase the amount of vector feathering applied, in real time it takes just one click to apply feathering to a selected object. Feathers (bitmap or vector) can be profiled in a similar fashion to fills and transparencies. Once a feather has been applied, click on the profile button to the immediate right of the feather slider to reveal the profile dialogue (Figure 2.2). 5

6 Figure 2.1. To feather an object, simply select it, and use the feathering slider on the main toolbar to apply feathering in real time. Figure 2.2. Feathers can be profiled using the profile dialogue. 2.2 Bitmap feather This type of feathering is very similar to vector feathering, but has subtle differences discussed in section Applying a bitmap feather is done through the use of the Live Effect (LE) tool; that is, bitmap feathering is a Xara-developed Live Effect. 6

7 To apply a bitmap feather, simply select the object to be feathered, select the Live Effect tool, click on the New button on the infobar, and select Bitmap Feather from the drop-down list of LEs available as shown in Figure 2.3. This applies the bitmap feather to the object, and the same slider used for vector feathering can be used to alter the feathering amount. Figure 2.3. To apply a bitmap feather, select the object, click on the Live Effect (LE) tool, click on the New button on the infobar, and select Bitmap Feather from the dropdown list Uses of bitmap feathering Bitmap feathering can be used for several reasons. Its primary use is to allow the feathering of bitmaps (or bitmap filled shapes) while ignoring the alpha channel (the transparent sections). Normal vector feathering would not feather the bitmap in this way the edges of bitmap would be feathered as a whole (rectangular) object. This is highlighted in Figure 2.4. As can be gathered from the name, a bitmap feather applies a bitmap effect to an object (whether it be a vector initially or not). Unlike vector feathering, this therefore means it is limited to a fixed resolution. To highlight what this means, Figure 2.5 shows what happens when the bitmap feather resolution is changed. Notice how the feathering effect itself does not ever appear pixelated, but that the object on which a bitmap feather is applied is forced to the resolution set on the LE infobar. This can be the default 96 dpi (screen resolution), or a higher or lower value depending on the resolution of the bitmap that the bitmap feather is being applied to. If a bitmap feather is applied to a bitmap, there is no need to increase 7

8 the bitmap feather resolution any higher than the native bitmap resolution, as it will produce no significant visual difference; for example, use a 96 dpi bitmap feather for a 96 dpi bitmap. Higher resolutions of bitmap feathers take greater processing power, and can slow down rendering. Figure 2.4. An example of the principal distinction between vector and bitmap feathering. Vector feathering feathers the edges of the whole (rectangular) bitmap, whereas bitmap feathering feathers the edges of the non-transparent part of the bitmap (that is, ignoring the alpha-channel of the bitmap). Note that the profile of the feather has been purposefully altered to exaggerate the effect. 8

9 Figure 2.5. A 300 dpi bitmap with alpha channel is given a bitmap feather. The resolution of the bitmap feather can be set in the Live Effect tool infobar. The image is re-rendered at whatever resolution is set for the bitmap feather. Lowering the resolution of the bitmap feather below the native resolution of the bitmap causes the bitmap to be rendered at that lower resolution. There is no significant visual difference in applying a bitmap feather at a resolution higher than the resolution of the bitmap it is being applied to, and in fact there would be a performance impact. In contrast, a vector feather is truly resolution independent. To understand this, it is necessary to understand what vector graphics are. All images displayed on screen in Xara are bitmaps including the vectors. This is because a monitor (in particular an LCD screen) is not an oscilloscope, which could literally draw physical lines, or at least does not display like one. Specifically, resolution independence means that no matter what zoom value 9

10 chosen to observe a (feathered/vector) object at, it is always re-rendered at screen resolution (i.e. no visible pixilation) for display. This means that as an object is zoomed into, the object must be re-rendered at screen resolution again, which at higher zooms means a larger, higher effective resolution of displayed bitmap. Thus the vector feather is being applied to an even bigger bitmap at these higher zooms. This is why as a vector feathered object is zoomed into, the redraw time becomes longer; zooming in by twice as much effectively increases the size of a 50 pixel feather to a 100 pixel feather on a bitmap twice as large and detailed. It is also similar to the reason why larger feathers of say 50 pixels take longer to draw than 25 pixel feathers. A bitmap feather set to 96 dpi remains 96 dpi regardless of how far the image is zoomed into. While resolution independent vector feathers thus strictly have no advantage over bitmap feathers for bitmapped objects, they are essential for vector objects such objects always need to be redrawn at higher effective resolutions as they are zoomed into to maintain resolution independence (i.e. always be displayed at 96 dpi). To highlight this, Figure 2.6 shows how a vector object is displayed with each type of feathering. Some other drawing applications only support bitmap feathering, and this is clear when a vector object with bitmap feathering applied is zoomed into, and the pixels become visible (unblurred in some cases) which totally defeats the purpose of using vector graphics. Only rarely would a bitmap feather be used on a vector object; conversely a vector feather would be frequently used on a bitmap unless the alpha channel was to be ignored, in which case a bitmap feather would be used. 10

11 Figure 2.6. Applying a bitmap and vector feather on a vector object shows the distinction between the two feathering types. Here, the profile of the feather in both cases has been purposefully altered to highlight the pixel edges (essentially turning the smooth feathering gradient off to emphasise the difference). The 30 dpi bitmap feather remains 30 dpi at all zoom factors; the resolution independent vector feather is recalculated and displayed at 96 dpi at any zoom factor. 3 Feathering versus Gaussian blurring Gaussian blurring is a technique used to blur the whole vector object like defocusing. It is a bitmap effect and the blurring can simulate the edge-softening effects of feathering. Most other software offers Gaussian blurring, but if the purpose is to soften just the edges, Gaussian blurring is not a suitable choice. To blur an object in Xara, the Live Effect tool must again be used. Simply select the object to be blurred, select the Live Effect tool, click the New button on the infobar, and select the Enhance Live Effect as shown in Figure 3.1. This reveals the Enhance dialogue. 11

12 Figure 3.1. To apply a bitmap feather, select the object, click on the Live Effect (LE) tool, click on the New button on the infobar, and select Enhance from the dropdown list. The Enhance dialogue appears. The bottom right control symbolised by is a blur and sharpen control combined. Dragging the slider to the left applies a Gaussian blur to the selected object in real time as shown in Figure

13 Figure 3.2. A 96 dpi Gaussian blur is applied to a 96 dpi bitmap. The LE tool infobar can be used to alter the blur effect resolution. Note: While Gaussian blurring is no substitute for feathering, there is one interesting caveat with Xara s implementation of feathering. When feathering objects with sharp points, the feathering process can generate, at times, noticeable artefacts. This is due to how points are feathered relative to edges, and is highlighted in Figure 3.3. Usually, this is not noticeable, but is something to bear in mind. 13

14 Figure 3.3. Feathering can introduce artefacts at sharp points; Gaussian blurring does not. The artefacts are infrequently noticed however. 4 Final comments Feathering is an exceptionally powerful feature, and very few graphics software to date offers true vector feathering, and certainly not with the same level of slickness offered by Xara. In general, it is rare that there would be a need to use a bitmap feather on a vector object. Bitmap feathers would most frequently be used on bitmaps when the alpha channel was to be ignored. Most of the time, a vector feather is most suitable for feathering needs. Xhris 14