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Hell On Earth > Hints > Importing 8-Bit Transparencies into CorelXara

Importing 32-Bit Images into CorelXara

Transferring 8-Bit Transparencies from a Bitmap Application

On this page:

Overview: 1-Bit Transparencies / The Single-Bit Problem

General Description: Summary / Steps

Comments

The Tutorial:

Start Tutorial

Warning: Lots of graphics ahead. The tutorial encompasses a total of three HTML pages with 220 kbyte in graphics.

Overview

CorelXara can only import images with 1-bit transparencies (GIF images). This means that imported images with transparency are limited to a total of 256 colors and that the transparent area will have a jagged edge.

With a workaround, Xara can import full-color 24-bit images from a bitmap editing application with full 8-bit transparency.

1-Bit Transparencies

GIF images have 1-bit transparencies; this means that any one pixel of the image is either visible or transparent. Other image formats such as PNG support 8-bit transparency.

With 8-bit transparencies, a pixel can be displayed in one of 256 stages of transparency, from opaque to completely invisible with 254 states in between. This way, you can produce see-through surfaces.

The Single-Bit Problem

This image of a photograph with a displaced glass frame illustrates the problem of single-bit transparencies.

Tutorial Image, 4k

You can reduce this image to 256 colors, save it as a GIF, define the grey background to be "transparent" and import it into Xara.

In the original image, the area where the displaced glass rests over the background is semi-transparent: When you change the background color in the original image, you can see this change behind the glass.

After importing the image as a GIF, this semi-transparent area will be lost: it will always display the background of the original bitmap and the background will no longer "shine through".

With the standard GIF import feature, the image loses everything that made it special: The color range as well as the flexible transparency. In order to keep both features, one has to work around certain software limitations.

General Description

Advanced users of bitmap graphics applications and CorelXara can probably figure the details out by themselves after reading a brief summary of the procedure, below.

Less advanced users might want to run through the full tutorial. The tutorial uses Photoshop and Xara; other applications should work just as well.

Summary

In a bitmap editing application, the bitmap image is created with an 8-bit transparency mask. The transparency mask is exported in 8-Bit grayscale, separate from the full-color image. In Xara, both mask and image are imported as bitmaps. With the bitmap image selected, the grayscale image is defined as transparency.

For best effect, when importing the image and map, they should already be rendered at the resolution needed for final output (print, web or otherwise).

Steps

  1. In the bitmap editing application, an 8-bit transparency mask is created for the image.
  2. The mask and the image are exported separately with identical image dimensions.
  3. The mask and image are imported into CorelXara.
  4. The mask is assigned to the bitmap as its 8-bit transparency definition.

Comments

With a bit of tweaking by its developers, CorelXara could surely be adapted to import 32-bit PNG images (The Portable Network Graphics format offers 24-bit lossless compression with 8-bit transparency).

Xara Ltd., the makers of CorelXara, even have the means to include this feature, since they have incorporated this technology into their Xara3D product (since version 2.0).

The state of visibility is usually stored in a separate color channel, also called a mask (because it masks out the parts of the image that are to remain invisible).

24-bit PNG graphics with an 8-bit transparency are commonly referred to as 32-bit PNG (24+8); hence the title of this section.

Begin with the Tutorial

Hell On Earth > Hints > Importing 8-Bit Transparencies into CorelXara 2

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