Photoshop Tutorials

Resolution and Image Sizes

 

Resizing Images for DTP in Photoshop

How to resize images in Photoshop, and maintain the best image quality.

 

When using images in a desktop publishing or illustration application, it is important to set the images to the correct resolution and size before you place them into your design. This way you will be able to achieve optimum image quality and it will also will mean that you do not have unnecessarily large image files which will slow down your computer and take longer to print.

 

Crop The Image

Start by using the crop tool, from the tools palette, to remove unwanted areas from the edge of the image or if necessary to change the proportions of the width and height.

 

Start to Resize Your Images

Use the Image Size command to adjust resolution and image dimensions: Image > Image Size.

For best results when resizing photographs and scanned images, first use the Image Size command and then sharpen slightly with the Unsharp Mask filter: Filter > Sharpen > Unsharp Mask.

You can resize images in a number of stages, sharpening slightly after each resize, or after every other resize, will help to prevent the image from becoming blurred as the image size is reduced.

300dpi resolution should be suitable for most general purpose print work, unless you are sending the job to a newspaper or your printer tells you a specific resolution for the job.

 

Changing Resolution and Image Size

Changing image resolution

If you want to change the image resolution without throwing away image information,
uncheck Resample Image then make your changes.
- Your file size will stay the same (i.e. the image still contains the same amount of information - and the same number of pixels.
- The print size will decrease as you increase the image resolution. (see stage 1 of the example below)
One example of this use would be if you have files from a digital camera - which are 72dpi - and your files for printing need to be 300dpi.

 

Changing image print size

If you want to make the print size of your image smaller, then you need to check the Resample Image box.

This will add pixels to the image or remove pixels from the image depending on the values you enter.

* If you also want the image to scale proportionally, check the Constrain Proportions box.

 

Example of the image resizing process

Resize a 10.1MB file scanned on a negative scanner to the correct size to be used in a page design to be printed.

Current size 1.57cm wide x 1.98cm high @ 2700dpi.
Desired size: 3cm x 3cm @ 300dpi.

1) Go to Image > Image Size and with Resample Image unchecked, change the image resolution to 300dpi. Click OK. The image print size will now be 14.13cm x 17.82cm @ 300dpi and still 10mb file size.

2) 2a) Go to Image > Image Size and this time make certain that both Resample Image and Constrain Proportions are checked.

We need to reduce the Print Size values for height and width by around 25%. This will reduce the file size by something like 50%.

So for the Width, change the measurement units drop-down menu to Percent and enter 75%, Click OK.

The height value will automatically change to keep the image dimensions proportional - if as Constrain Proportions is checked.

2b) Use the Unsharp Mask filter to sharpen the image slightly.
Filter > Sharpen > Unsharp Mask.
Change the settings to suit your image, but the following values should work OK.
Amount: 50 - 70,
Radius:1 - 1.2,
Threshold: 5.
If you see a huge difference in the sharpness of your image then you have probably got the value for the amount or radius settings too high and you will need to reduce them slightly.

3) Go to Image > Image Size and again with Resample Image and Constrain Proportions checked: Again reduce the print size by around 25%
Run Unsharp Mask again, with similar settings to before - but maybe slightly lower amount and radius settings.

4) Repeat the resizing and sharpening until the image width is 3cm or whatever value you need for your page design. Your image should now be 3cm wide x 3.78cm high

 

You can use the Canvas Size command to adjust the dimensions of the image so that it fits into your page design.

If for instance you wanted the image to be exactly 3cm x 3cm then the Canvas Size command Image > Canvas Size will allow you to selectively and accurately crop either the height or width of the image and choose which side of the image is trimmed and which remains unchanged.

 

Save the file as a Tiff, EPS or JPG and place into the page in your illustration or desktop publishing document.

 

If you have a number of images to process, the resizing and other modifications can be speeded up by using Actions to record and then play back a number of processes automatically or semi-automatically on each image.