|
Basic Edits: Resizing
If you have not read the previous section on image size and PPI/DPI, click here to read it now. It is important to understand this before you actually start changing the size of your images as shown here. I'll wait right here!
Ok ... you're back. Good.
The size of an image is simply the number of pixels in it - for example an 8 megapixel Canon EOS 350D creates an image with a size of 3456 × 2304. However when you combine this pixel size with a pixels per inch (PPI) value (see section 8.4.1) you can also talk about the images physical dimensions. A Canon 350D image printed at 300 ppi will give an image of 11.5” × 7.7”. If you print the same image on 6×4 paper, your print will be 576ppi.
When resizing an image, you need to be careful whether you want to resize the pixel dimensions of the image or the physical image size (measured in centimetres or inches). Resizing is done by selecting ‘Image Size’ from the Image menu.
Pixel Resizing
You might want to do this if you want to reduce the filesize for e-mailing to someone, or for uploading onto a webpage or photo sharing site. You can usually do this by specifying a new pixel dimension or by specifying a percentage change.
The resize dialog box will also have a check box to lock the aspect ratio - this means that if you specify one of the dimensions, the computer will automatically fill in the other one so as not to squash or stretch the image.
When you elect to resample an image - you will often be confronted with a series of options for which resampling technique should be used. The most common are either pixel resize, or bicubic resampling. To illustrate the difference, I have used a company logo - it is not uncommon for companies to have to size down a logo image for use on a website.
 |
Original logo - accurately resized to fit the box on the left. |
 |
The pixel resizing technique has been used here to create an image 150 pixels wide (but scaled up here so you can more easily see the effect). |
 |
This image is the same size as the one above (150 pixels wide) although the bicubic resampling technique has been used. |
 |
Pixel resize again - this time down to only 80 pixels wide. The text is very hard to read. |
 |
Bicubic resampling again at only 80 pixels wide. Move back from your monitor and you will see it is more readable that the pixel resize, although a consequence of this technique is a lighter image. |
The resize feature in Paint Shop Pro (versions XI and XII) works in exactly the same way as Photoshop but with the addition of a sharpness slider. This is useful when dropping the image size down by a large amount which tends to soften an image, although it is easily done as an extra step in any image editing package.
We would always recommend sharpening an image after reducing it’s size - see the later section on image sharpening for details on how to do this.
Resizing for printing
For this, you generally don’t want to change the image data at all - you simply want to alter the PPI so that the image comes out the size you require. Most software does this for you at the printing stage and you don’t need to use the image size feature at all. However you can use it to set the PPI value in the file. For this you MUST uncheck the ‘Resample Image’ box – this will lock the pixel dimensions of the image. When you specify the size you require, all that photoshop will do is compute the correct PPI value and store this in the image file so that when you print the image at 100% scaling, it will come out the size you specified.
|
The image on the right shows Photoshop's options in the print dialog box for controlling the print size. As you can see, the resize operation mentioned in the previous paragraph was unnecessary as you can also specify the exact print size here – the only difference being that the PPI value is not stored in the file for later.
By selecting the size of paper you require and selecting ‘fit to page’ or specifying a custom print size in the print dialog, your computer will take care of scaling the image data to perfectly fit the size requested.
If you have cropped the image as shown in the previous section by specifying exact dimensions and leaving the resolution box blank, then you also will have stored the correct PPI value, and therefore printing with a scale value of 100% gives you the size you specified in the crop process. |
 |
|
Photographs
This is a site about photography so I'm sure you are expecting to see plenty of pictures.
For now, why not take a peek at the flickr galleries belonging to the two authors of this site.
Colin's Flickr Page
Phil's Flickr Page
"Classic Quote"
- Quote by
|
