• Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL
Help

Chapter 4. Pixel Basics > Changing dimensions and resolution

Changing dimensions and resolution

To change an image’s pixel dimensions for onscreen output:

1.
Choose Image > Image Size.

2.
Make sure Resample Image is checked , and choose an interpolation method from the pop-up menu. Bicubic degrades the image the least but also takes the longest.


Check Resample Image and enter a Document Size: Resolution of 72 pixels/inch in the Image Size dialog box.


3.
To preserve the image’s width-to-height ratio, leave Constrain Proportions checked.

4.
Set the Resolution to 72 pixels/inch (or “ppi,” for short).

5.
Enter new Pixel Dimensions: Width and/or Height values.

6.
Click OK.

To change an image’s dimensions for print output:

1.
Choose Image > Image Size.

2.
To preserve the image’s width-to-height ratio, check Constrain Proportions. To modify the image’s width independently of its height, uncheck Constrain Proportions.

3.
Optional: To preserve the image’s resolution, check Resample Image and choose Nearest Neighbor, Bilinear, or Bicubic as the interpolation method. Bicubic causes the least degradation in image quality.

4.
Choose a unit of measure from the pop-up menu next to the Document Size: Width and Height fields.

5.
Enter new Width and/or Height values, corresponding to the physical dimensions you’ve chosen for the printed image. The Resolution will change if Resample Image is unchecked.

6.
Click OK.

Tip

To restore the original Image Size dialog box settings, Alt-click/Option-click Reset.


Tip

File > Print with Preview can also be used to resize or rescale print dimensions, but it doesn’t preserve the image resolution.


Previewing the print

To see the image size relative to the paper size, press and hold on the status bar at the bottom of the image window or choose File > Print with Preview.


To see the image size relative to the paper size, press and hold on the status bar at the bottom of the image window.


To display the image onscreen at the size it will print, choose View > Print Size. The screen (display) size of an image is determined by the image’s pixel dimensions and the monitor size and setting, whereas the display of the print size of an image is determined by the image’s pixel dimensions and resolution—the number of pixels viewed per unit of printed length (usually inches). So for a high-resolution image at a 100% zoom level, choosing View > Print Size will display the image at an approximation of its actual printout size—not necessarily the physical printout size.


Note: If you increase an image’s resolution (resample up) with Resample Image checked, pixels will be added and the image’s file storage size will increase, but its sharpness will diminish. If you decrease an image’s resolution (downsample), information will be deleted from the file, and it can only be retrieved using the History palette before the image is closed. Blurriness caused by resampling may only be evident when the image is printed; it may not be discernible onscreen. That’s why it’s always best to scan or create an image at the proper resolution. Follow the instructions on pages 84–85 to resharpen a resampled image. (See also pages 53 and 56.)

To change an image’s resolution:

1.
Choose Image > Image Size.

2.
To preserve the image’s dimensions (Width and Height), check Resample Image , and choose an interpolation method from the pop-up menu.



or

To preserve the image’s total pixel count, uncheck Resample Image. The Width and Height dimensions will change to preserve the current pixel count.

3.
Enter a Resolution value.

4.
Click OK.

Tip

The History Brush tool won’t work on a resampled image. You’ll only be able to set the source for the History Brush tool from the current state forward.


Cash in on a high resolution

An image contains a given number of pixels after scanning, and its print dimensions and resolution are interdependent. If an image’s resolution or dimensions are changed with Resample Image unchecked in Image > Image Size, the file’s total pixel count is preserved. Increasing an image’s pixels-per-inch resolution will shrink its print (physical) dimensions; lowering an image’s pixels-per-inch resolution will enlarge its print dimensions.

If your file has a higher resolution than needed (more than twice the screen frequency), you can allocate the extra resolution to the print size dimensions by unchecking Resample Image (the Width, Height, and Resolution are now interdependent), and then lowering the Resolution to twice the screen frequency. The width and height values will automatically increase, and the file storage size and pixel dimensions will remain constant—no pixels will be added or deleted from the image.

If you must further enlarge the image’s dimensions, click in the Width field, check Resample Image, then enter a new Width value. The Height value will change proportionately, and the file storage size and pixel dimensions will increase. The image will be resampled, though, so after clicking OK, apply the Unsharp Mask filter to resharpen.


The Fit Image command has no effect on an image’s resolution—it only changes its physical dimensions. Use it to make an image smaller.

To resize an image to fit a specific width or height:

1.
Choose File > Automate > Fit Image .


Use the Fit Image command to change an image’s dimensions without changing its resolution.


2.
Enter a Width or Height value in pixels. The other field will automatically adjust after you click OK, so the width-to-height ratio will stay the same.

3.
Click OK.

The Resize Image command duplicates an image and resizes the duplicate automatically. All you have to do is respond to a sequence of dialog boxes—Photoshop will figure out the math for you.

To resize an image automatically:

1.
Choose Help > Resize Image.

2.
Click Print or Online , then click Next.


Click Print or Online.


3.
Enter the desired output dimensions , then click Next. If you chose Online in the previous step, click Finish now. For print output, follow the remaining steps.


Enter the desired print size.


4.
Click or enter the LPI as per your print shop’s instructions , then click Next.


Click or enter the LPI that your print shop specifies.


5.
Move the Quality slider , then note the final image size in the Results area. If there’s a message below the Results area, read that as well. If you want to proceed, click Next.


Move the slider to the desired image quality.


6.
Click Finish , and then save the resized image. (Or click Cancel.)


Click Finish.


If you change an image’s dimensions or resolution with Resample Image checked, convert it to CMYK Color mode, or transform it, blurring may occur due to the resampling process. To help correct this, you can apply the Unsharp Mask filter, which despite its name has a focusing effect. The filter increases contrast between adjacent pixels that already have some contrast. You can specify the amount of contrast to be added (Amount), the number of surrounding pixels that will be modified around each pixel that requires more contrast (Radius), and determine which pixels the filter affects or ignores by specifying the minimum contrast (Threshold).

Note: The Unsharp Mask effect may be more noticeable onscreen than on highresolution print output.

To apply the Unsharp Mask filter:

1.
Choose Filter > Sharpen > Unsharp Mask .


The original image, which is a bit blurry


2.
Choose an Amount for the percentage increase in contrast between pixels (and , next page). Use a low setting (below 50) for figures or natural objects; use a higher setting if the image contains sharp-edged objects. Too high a setting will produce obvious halos around high-contrast areas. The larger the image, the less sharpening may be required. For a high-resolution image, use an Amount between 150 and 200 percent.


When using the Unsharp Mask dialog box, start with conservative Amount, Radius, and Threshold settings.



After Unsharp Masking with a high Amount (160), Radius 1.5, and Threshold 0: Note the halos around the edges and centers of the flowers.


3.
To choose an appropriate Radius value, which is a little trickier, you need to factor in the final size, the resolution, and the subject matter of the image. The Radius value (0.1–250) controls the number of pixels surrounding high-contrast edges that will be modified (, next page). Try between 1 and 2 pixels. A higher value could produce too much contrast in areas that are already high-contrast.


After Unsharp Masking with a high Radius (6.0), Amount 130, and Threshold 0: The soft gradations have become choppy and the image has an unnatural contrast and sharpness.


The higher the resolution of the image, the more pixels there are on the border between high-contrast areas, and thus the higher the Radius setting is required. Try a high Radius setting for a low-contrast image, and a lower Radius setting for an intricate, high-contrast image.

Note: The higher the Radius setting, the lower the Amount setting can be, and vice versa.

4.
Choose a Threshold value (0–255) for the minimum amount of contrast an area must have before it will be modified . At a Threshold of 0, the filter will be applied to the entire image. A Threshold value above 0 will cause sharpening along already high-contrast edges, less so in low-contrast areas. If you raise the Threshold, you can then increase the Amount and Radius values to sharpen the edges without oversharpening areas that don’t require it. To prevent noise from distorting skin tones, specify a Threshold between 8 and 20.


After Unsharp Masking with a high Threshold (15), Amount 160, and Radius 1.5: Even with the same Amount setting as in the top image, the soft gradations in the petals and the background are preserved.


5.
Click OK.

Tip

To soften a grainy scan, apply Filter > Blur > Gaussian Blur at a low setting (below 1), and then apply Filter > Sharpen > Sharpen Edges once or twice afterward to resharpen.


Tip

To avoid waiting for the full screen Unsharp Mask preview on a large image, first get close to the desired settings using just the preview window with Preview unchecked; then check Preview to preview the results on the full screen; and finally, readjust the settings, if needed.


Tip

Try applying the Unsharp Mask filter to one or two individual color channels (for example, just the Red or Green channel in an RGB image). If you sharpen two separate channels, use the same Radius value for both. You can also convert an image to Lab Color mode and then apply the filter to the L channel to sharpen luminosity without affecting any color pixels.


  • Creative Edge
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint