Sunday, October 26, 2008

Resizing vs. Resampling

By David Peters

First things first, there IS a difference between photo resizing and resampling. Although they are both a Photoshop tool designed to change the size of an image, using the two terms interchangeably is not accurate. The method of resizing and resampling is actually performed differently. This difference is determined by how the image itself is changed. If this sounds complicated, it's really not. One small checkbox option defines the two. Opening the Image Size dialog box, you will see a checkpoint option at the bottom corner. This is the box you choose to resize or the resample of the image.

Under the Image Menu at the top of the screen, will be what is called the Image Size dialog box. This again is the one option determining resizing or resampling. An image is actually composed of tiny dots of color together called pixels. How the number of pixels is changed or not changed defines resizing versus resampling the image. Photoshop terminology refers to this as altering the pixel dimensions. Keeping the pixels number the same and only changing the size you wish the picture to print is called resizing. Photoshop refers to this is changing the document size of the image. But, if you in fact change the amount of pixels making up the image, it is known as resampling.

Image Resizing: Changing the size the image will print without changing the number of pixels in the image. Image Resampling: Changing the number of pixels in the image.

It is pretty simple once you know the difference, but how does it relate to your computer and how hard is this to really do? You can do this quickly and easily with your own photos in just a few simple steps

Resizing vs. Resizing An Image

We're not quite done yet with the Image Size box. It also contains three other pieces of information as shown below: Scale Styles - Deals with the affect of resizing or resampling the image on Layer Styles. Constrain Proportions - Enabled by default, it links the width and height of the image together. If you make a change to the width of the image, for example, Photoshop will automatically change the height, and vice versa, so that the proportions of the image remain the same and don't get distorted. Resample Image - THIS IS THE KEY HERE!!!

Also in the Image Size box are three more options below the Document Size section: Scale Styles - Deals with Layer Styles and how they're affected by resizing or resampling the image. Constrain Proportions - Enabled by default, links the width and height of the image together. If you make a change to the width of the image, for example, Photoshop will automatically change the height, and vice versa, so that the proportions of the image remain the same and don't get distorted. Resample Image - THE IMPORTANT ONE!!!

If unchecked, the Resample Image will only display the number of pixels or both the height and width in the Pixel Dimensions blocks of the dialog box, but they are visible just for information purposes. The pixels values will not be able to be changed. Only the image print size can be changed by using the Document Size section. With Resample Image checked, the pixel dimensions are shown inside white input boxes which we can click inside of and type in new values, changing how many pixels are in our image.

With the Resample Image unchecked, the Pixel Dimensions sector of the dialog box will show how many pixels are in the image for the width and height, but you will no longer be able to change those numbers. They're visible for information only. The only option available is to change how large the image will print using the Document Size section. With Resample Image checked, the pixel dimensions are shown inside white input boxes which we can click inside of and type in new values, changing how many pixels are in our image.

There are also a few other changes that happen depending on if the box is left checked or unchecked. The Scale Styles and Constrain Proportions options at the bottom of the Image Size dialog box are grayed out when Resample Image is not checked. Scale Styles is grayed out because it's only an issue when the number of pixels in an image is being altered. Since the pixels number of the image remains the same with Resample Image unchecked, the Scale Styles is not needed.

Image Interpolation Options When Resampling Images

Image Interpolation Options When Resampling Images

One more box is grayed out when the Resample Image box is unchecked. To the right of the Resample Image option is a drop-down box called either 'Bicubic Sharper' or simply 'Bicubic.'

These options will be grayed out because they only will work for images that are being resampled. If all you are doing is changing how large or small the image will print on paper, you won't need these options.

Summary Image resizing - Keeps the number of pixels in your image the same and affects only how large the image will print (the Document Size). Image resampling - Physically changes the number of pixels in the image (the Pixel Dimensions). Resample Image - Option located at the bottom of the Image Size dialog box that controls if you are resizing or resampling the image. Checking the Resample Image, means you are resampling the image. Unchecked, you're simply resizing the image. Resample images by changing width and height values in the Pixel Dimensions section of the Image Size dialog box. It is used mostly when optimizing images for the web or computer screen. Resizing images by changing the width, height and/or resolution values in the Document Size section of the Image Size dialog box is used for printing the image.

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