Image Resizing

Resampling refers to changing the pixel dimensions of an image. When you down sample (decrease the number of pixels), information is deleted from the image. When you resample up (increase the number of pixels, or up sample), new pixels are added. You specify an interpolation method to determine how pixels are added or deleted.

Resampling pixels

Keep in mind that resampling can result in poorer image quality. For example, when you resample an image to larger pixel dimensions, the image loses some detail and sharpness. Applying the Unsharp Mask filter to a resampled image can help refocus the image details to some degree.
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Choosing an interpolation method

When an image is resampled, an interpolation method is used to assign color values to any new pixels that Photoshop creates, based on the color values of existing pixels in the image. Photoshop uses sophisticated methods to preserve the quality and detail from the original image when you resample.

In the General Preferences dialog box, you can specify which default interpolation method to use whenever you resample images using the Image Size or transformation commands. The Image Size command also lets you specify an interpolation method other than the default.

To specify the default interpolation method :

For Interpolation, choose one of the following options:

  1. Nearest Neighbor:  A fast but less precise method that replicates the pixels in an image. This method is for use with illustrations containing edges that are not anti-aliased, to preserve hard edges and produce a smaller file. However, this method can produce jagged effects, which become apparent when you distort or scale an image or perform multiple manipulations on a selection.
  2. Bilinear:  A method that adds pixels by averaging the color values of surrounding pixels. It produces medium-quality results.
  3. Bicubic: A slower but more precise method based on an examination of the values of surrounding pixels. Using more complex calculations, Bicubic produces smoother tonal gradations than Nearest Neighbor or Bilinear.
  4. Bicubic Smoother: A method for enlarging images based on Bicubic interpolation but designed to produce smoother results.
  5. Bicubic Sharper: A method for reducing the size of an image based on Bicubic interpolation with enhanced sharpening. This method maintains the detail in sampled image. If Bicubic Sharper over sharpens some areas of an image, try using Bicubic.

To change the pixel dimensions of an image

Choose Image > Image Size.

  1.  To maintain the current ratio of pixel width to pixel height, select Constrain Proportions. This option automatically updates the width as you change the height, and vice versa.
  2. Under Pixel Dimensions, enter values for Width and Height. To enter values as percentages of the current dimensions, choose Percent as the unit of measurement. The new file size for the image appears at the top of the Image Size dialog box, with the old file size in parentheses.
  3.  Make sure that Resample Image is selected, and choose an interpolation method.
  4. If your image has layers with styles applied to them, select Scale Styles to scale the effects in the resized image. This option is available only if you selected Constrain Proportions.
  5. Click OK.

Plug-ins

Extensis pxl SmartScale

With Extensis SmartScale, you can resize digital images up to 1600% of the original size with no discernable loss in print quality. The resulting scaled image maintains the quality and details of the original. SmartScale gives you the ability to easily choose scale settings and immediately preview the results.

Using the PixelLive technology, SmartScale creates superior quality scaled images by preserving the brightness and color data of the original image. SmartScale analyzes the original image and stores the brightness and color information in a mathematical equation. SmartScale resamples the image to the new size and then applies the color and brightness information to the scaled image. The final result is a superior quality scaled image. You can easily open and scale images directly from Photoshop using the Extensis menu. SmartScale also shows you a preview of the scaled image, making it easy to scale, crop and adjust image settings using the familiar, intuitive tools.

If you have an image open in Photoshop, you can scale that image with SmartScale and return the results to Photoshop.

  1. Open an image in Photoshop.
  2. Choose Extensis > pxl SmartScale > Scale Current Image
  3. Scale the image using the Image Size palette, then adjust your results in the Detail palette. The image can also be cropped with the Crop tool and Crop palette.
  4. Click Apply to send the the image in Photoshop.

You can scale an image to precise dimensions by entering the new dimensions in the Pixel Dimensions or Document Size group box of the Image Size palette.



1. Open an image in Photoshop.

2. Choose Extensis > pxl SmartScale > Scale Current Image

3. In the Image Size palette, enter the width or the height in the Document Size group box. The opposite dimension adjusts proportionally.

4. Check the opposite dimension and do one of the following steps:
• If the opposite dimension is the desired scale size, the scaled size is proportional to the original. Go on to step
• If the opposite dimension is smaller than desired, start over and scale to this dimension.
• If the opposite dimension is larger than desired, crop the image with the crop tool and go on to step 5.

5. Adjust the Detail settings as desired and click Apply to return the scaled image to Photoshop.

Scaling an image by a percentage

1. Open an image in Photoshop.
2. Choose Extensis > pxl SmartScale > Scale Current Image
3. In the Image Size palette, in the Pixel Dimensions group box, choose Percentage from either drop down box.
4. Enter the desired scale percentage in the text box. The opposite pixel dimension adjusts proportionally.
5. Adjust fine tune settings as desired and click Apply to scale the image.
Scaling an image to a precise resolution

1. Enter the desired resolution in the Resolution box on the Image Size palette.
The pixel dimensions are automatically adjusted, but the document size dimensions are not affected.