Resizing images

After you adjust your image, you can resize it. It’s important to understand how resizing affects image pixels.

Effect of resizing on image resolution

Pixels have no set physical size. Each pixel represents one sample of a single color. When an image is resized, the number of pixels in the image may be reduced or increased, which causes the image to be resampled. Resampling changes the file size.

Print resolution is defined as the number of pixels per inch (ppi). A higher print resolution creates smaller printed pixels and therefore a smaller printed image. A lower print resolution creates larger printed pixels and a larger printed image. Resizing can be used to do the following

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change the print resolution and print size while preserving the number of pixels and file size (no resampling)

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change the number of pixels and file size while preserving the print resolution and print size (resampling)

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change the print resolution, print size, number of pixels, and file size (resampling)

Consider these guidelines when you resize your images:

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Avoid increasing the image size by more than 125%. Doing so may cause a loss of detail and sharpness.

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Resize an image only once. If you resize the image incorrectly, undo it and try again.

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Correct and retouch images before resizing.

Resampling methods

The Resample option lets you specify how pixels are changed in an image. The Bicubic method is the slowest method, but it usually produces the best results.

The resampling types available in Corel PaintShop Pro are described in the following table.


Resampling type	Description
Smart Size	Chooses the best algorithm based on the new pixel dimensions you set
Bicubic	Minimizes the jaggedness that often results from expanded, irregular, or complex images
Bilinear	Uses the two nearest pixels around each existing pixel to determine the appearance of newly created pixels
Pixel Resize	Duplicates or removes pixels to achieve the selected width and height of the image (recommended for hard-edged images and simple graphics)
Weighted Average	Uses a weighted-average color value of neighboring pixels to determine the appearance of newly created pixels (useful for reducing photorealistic, irregular, or complex images)

What happens to pixels when you resample an image?

When you use the Resize command to increase the image dimensions, additional pixels must be interpolated from information in the existing pixels. Imagine that you have an image of 100 × 100 pixels, and that you want to enlarge the image by increasing the number of pixels to 200 × 200. You begin with 10,000 pixels and after resizing end up with 40,000 pixels. Thus, three-fourths of the final pixels are “made up.” Most methods of making up pixels involve interpolating the interpixel gaps produced by stretching the image dimensions. The Pixel Resize method copies the color of the nearest pixel. The Bilinear method is based on an average of four neighboring pixels (from a 2 × 2 pixel neighborhood). The Bicubic method is more sophisticated and uses 16 neighboring pixels (from a 4 × 4 pixel neighborhood). This larger neighborhood provides more information about how the color is changing in that particular part of the image and therefore can improve the colors in the made-up pixels.

When you use the Resize command to decrease the image dimensions, the pixel colors are averaged together. Imagine that you want to decrease an image from 100 × 100 pixels to 50 × 50 pixels. The result contains 2,500 pixels, which is one-fourth of the pixels used to represent the original image. The different resampling methods determine how much weight is given to the original pixels when they are averaged together.

Are there other ways to resize an image?

In addition to using the Resize command, you can also change the image size by changing the canvas size, cropping the image, printing at a different size, using the Copy Special command, or using the Save for Office command.

Increasing the canvas size adds pixels at the edge of the image. Decreasing the canvas size hides pixels at the edges of the image (full layer information is kept). For more information, see Resizing the canvas.

Cropping an image deletes the pixels outside the selected crop area. For more information, see Cropping images.

You can resize an image that you add to the Print Layout workspace by dragging its selection handles. Resizing the image in this way does not change the image file, which is helpful if you want to print the image at various sizes. For more information, see To resize an image in print layout.

The Copy Special command lets you copy the image to the Clipboard in one of three sizes, depending on whether you are copying the image to print professionally, to print from your desktop, or to copy to your computer screen or an e-mail message. After copying the image to the Clipboard, you can paste the resized image in a file in another application, such as a word processor. For more information, see Copying images into other applications.

The Save for Office command provides resizing options that are similar to those provided by the Copy Special command, except that you can save the file to disk as well as specify image size and resolution. For more information, see To save images for office applications.

Why are you resizing the image?

You can use the Resize dialog box more effectively if you know why you want to resize the image.

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If you want to use a very large photo on a Web page, or if you want to attach a large photo to an e-mail, you can use the Width and Height controls in the Print Size group box. In the Advanced settings area, you should ensure that the Maintain original print size check box is unmarked and that the Lock aspect ratio check box is marked.

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If you want to resize an image by a specific percentage or to specific pixel dimensions (for example, 800 × 600), you can use the controls in the Pixel Dimensions group box. In the Advanced settings area, you should ensure that the Resample using check box is marked.

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If you want to resize an image by changing only its resolution, you can unmark the Resample using check box in the Advanced settings area, and type or set a value in the Resolution control in the Print Size group box. Resizing an image in this way does not change the pixel dimensions of the image.

To resize an image by resolution or print size

Edit workspace

Choose Image

Resize.

The Resize dialog box appears.

Mark the Advanced settings check box.

Unmark the Resample using check box.

In the Print Size group box, type or set values in the Width, Height, or Resolution controls.

You can change the units of measurement by using the drop-lists next to the Width, Height, and Resolution controls.

Click OK.


You can also
Resample image pixels	Mark the Resample using check box, and choose a resampling method. Note: Resampling changes the image’s pixel dimensions and lets you change the resolution setting independently from the width and height settings.
Sharpen the resized image	Mark the Resample using check box, and choose Bicubic from the drop-list. Set the Sharpness control at approximately 100 to shrink an image; or at approximately 50 to enlarge an image. Note: When the Sharpness control is set to 0, the sharpness of the resized image does not change.
Preserve the brightness of the resized image	In the Miscellaneous options of the General Program Preferences dialog box, mark the Preserve image brightness when resizing check box.

When you unmark the Resample using check box, the Width, Height, and Resolution controls work together — a change to one control causes the other controls to change. When you use this method, the pixel dimensions of the image remains unchanged.

To resize an image by pixel dimensions or percentage

Edit workspace

ChooseImage

Resize.

The Resize dialog box appears.

Mark the Advanced settings check box to display the additional Resize settings.

Mark the Resample using check box, and select a resampling method from the drop-list.

The Bicubic method usually produces the best results, although it is also the slowest method.

If you want to resize the current layer only, unmark the Resize all layers check box.

From the drop-list in the Pixel Dimensions group box, choose either Pixels or Percent (to resize as a percentage of the original), and then type or set values in the Width and Height controls.

Click OK.

It is recommended that you constrain the new image dimensions to the image’s current proportions by marking the Lock aspect ratio check box. Changing the aspect ratio distorts the image by stretching or contracting it in one dimension more than the other. In the Print Size and Pixel Dimensions group boxes, a lock icon appears next to the Width and Height controls when the Lock aspect ratio check box is marked. Changing the setting of one of these controls automatically changes the setting of the other control.

You can preserve the image’s current print size by marking the Maintain original print size check box. When this check box is marked, a lock icon appears next to the Resolution control and the Width and Height controls in the Pixel Dimensions group box.