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Comparing Compression

Fireworks makes it easy to choose between different compression formats. Open the file temp_layout, which was created in Hour 2, so that you can see how different compression formats affect image quality and file size. (If you have not yet completed Hour 2, you will need to jump backwards to create the file and folder now.) Choose Open from the File Menu or press Ctrl+O (Windows) or Command+O (Macintosh). Select the file temp_layout from the Fireworks Examples folder.

With the Canvas open in your workspace, look up to find the tabs Original, Preview, 2-Up, and 4-Up above the Canvas and below the menus, as shown in Figure 3.1. These tabs let you switch between editing the original and previewing the export output. When you want to view or edit the source graphic, choose the Original tab (default). To preview how the output file will appear when exported into a different format, click on the Preview tab. The 2-Up and 4-Up tabs let you compare different types of compression at the same time. Click the Preview tab now to view the optimized output.

Figure 3.1. The view mode tabs include Original, Preview, 2-Up, and 4-Up.

To change the optimization settings, you can use the Optimize panel, as shown in Figure 3.2. Expand the Optimize panel in the dock by clicking the arrow next to its name. If the Optimize panel isn’t visible, choose Optimize from the Window menu or press F6.

Figure 3.2. The Optimize panel lets you fine-tune format settings.

At the top of the Optimize panel is a drop-down menu named Settings. This menu is where optimization presets are stored. The default setting is GIF WebSnap 128. If this isn’t the current setting, select it now. Now change the setting to JPEG—Smaller File (see Figure 3.3). Click the 2-up preview tab; then notice how the image preview on the right changes. Also, underneath the two previews is the file size and an estimate of how long it will take to download over a 56Kbps modem.

Figure 3.3. Heavy JPEG compression can blur image detail.

To compare the current setting to the original images, choose the 2-Up tab. The workspace will split into two—the left will represent how the original document appears; the right will preview the optimized file. To compare the original to different compression options, choose the 4-Up tab. The workspace will split into four windows, with the original image in the top left, as in Figure 3.4. Click a quadrant to change the optimization settings for that preview. This way you can preview a number of different compression settings at once, with the original as a reference.

Figure 3.4. The 4-Up preview mode allows you to compare and contrast optimization settings by eye.

Working with the Optimization Panel

With the workspace in 4-Up preview mode, get to know how to use the optimization settings by previewing the image and adjusting the settings for the best possible output with the smallest file size.

Task: Preview Different Compression Settings

In this task you will look at how different rates of compression and different file types affect an original image. Using this system of previewing and checking will ensure that your exported files are of the size and quality you require.

Click the upper right preview pane to select it.

On the Optimize panel, select GIF Web 216. Figure 3.5 shows the optimization settings for the upper right pane. This preset specifies GIF format, with the palette composed of the 216 colors that comprise the standard Web palette.

Figure 3.5. Selecting a pane allows you to choose optimization settings to preview in that pane.

Click the lower left preview pane.

On the Optimize panel, select GIF Adaptive 256. This preset specifies GIF format also, but the palette is chosen of colors that may change (adapt), depending on the available system palette.

Click the lower right preview pane.

On the optimize panel, select JPEG—Better Quality File. JPEG uses a fully accurate 24-bit palette, but detail in high-contrast and high-detail areas, like outlines, can be lost as part of the compression.

To examine the previews in detail, you can use the Zoom tool (press Z) to change the view magnification to 100% or more. This does not actually edit the image; it merely changes the way you see the file during the preview. Use the Hand tool (H) to change the view of the canvas and pan a particular area into view. Note how the different types of compression affect the temp_layout file differently. The line art will look jagged with GIF Web 216, and the photograph will be dithered, which means it loses detail. The photo will improve with the GIF Adaptive 256 setting, but the color of the line art may shift slightly because the adaptive palette will be skewed to the colors from the photograph. The colors will look most natural with JPEG, but the text and line art will seem slightly blurred, as shown in Figure 3.6, which shows temp_layout at a magnification of 300%.

Figure 3.6. You’ll notice the effects of different compression rates when you zoom in on the preview panes. Different elements of the image react differently to the compression settings.

Now compare the file sizes. This will be below the preview frame, listed in kilobytes, like in Figure 3.7, which shows a detail of the previous figure. The first GIF will be around 45 kilobytes. The next GIF will be around 51KB—it is larger because there are more colors in the palette. The JPEG will be about 37KB. The image should be around 30KB, and JPEG offers the best color depth and most control over compression, so you’ll select the lower right quadrant to work with.

Figure 3.7. Below the visual preview is a data preview detailing the export output file size and transfer time.

Click the 2-up tab above the canvas (see Figure 3.8). Since the JPEG frame had been selected in 4-up mode, it will now be the export preview choice on the right.

Figure 3.8. 2-Up preview compares the selected optimization settings for a closer comparison.

On the Optimize panel, notice the Quality value (80). For JPEG this represents the ratio of size to image quality—0 means the smallest size and worst quality; 100 means largest file and best quality. To the right is a down arrow. Click this to bring up the Quality slider. Using the slider, change the value to 70, as shown in Figure 3.9. The exported image preview and file size will update, and you should be well under 30KB.

Figure 3.9. Sliders are often used to adjust values in Fireworks. Values can also be typed in directly.

In this situation you are exporting the entire image as a single file, so you can use only one form of compression. Fireworks helps optimize by letting you slice an image into multiple parts and apply a different format and optimization setting to each part—such as GIF compression for the line art and JPEG compression for the photograph. Slicing images will be discussed in more detail in Hour 14, “Slicing Layouts.”

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