How To Use Adobe Photoshop CS2 - 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.

The top of the screen has the Image Menu, under this option will be what is called the Image Size dialog box. Here you will find the checkpoint determining resizing or resampling function. Pixels are the tiny dots of color that when grouped together form the image. Resizing or resampling the image happens depending on is the number f pixels changes or not. In Photoshop this is called changing the pixel dimensions. Changing only the size you wish the picture and saving the pixel number the same is called resizing. Photoshop calls this changing the document size of the image. Changing the number of pixels making up the image is referred to as resampling.

Image Resizing - Changes the size the image will print out as without changing the number of pixels in the image. Image Resampling - Changes the number of pixels in the image.

Doesn't seem like such a big deal now does it? The difference is pretty simple once explained just a bit. But how do you actually do this with your own photos? Let's walk through the 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!!!

We will talk some on Scale Style and Constrain Proportion, but let's look at that last box being checked or left blank. This check mark determines resizing versus resampling. While resizing keeps the pixel dimensions the same and only increases or decreases the size at which the image will print, resampling actually changes the number of pixels in the image. The Resample Image choice will be automatically checked. ven though the dialog box still says 'Image Size' at the top, but its unction is now is as the Image Resample dialog box when it is checked. Both the Pixel Dimensions and the Document Size and all of their options will be available to you.

We won't go into detail about the Scale Style and Constrain Proportion, because it is that last box that is the key to resizing vs. resampling. Keep in mind that resizing keeps the pixel dimensions the same and only changes the size at which the image will print, while resampling physically changes the number of pixels in the image. The Resample Image option will be checked by default. This means that even though the dialog box still says 'Image Size' at the top, it is now basically the Image Resample dialog box with the checkmark. All of the variables in both the Pixel Dimensions and in the Document Size will be available to you.

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.

You will find that Constrain Proportions is also grayed out when Resample Image is unchecked. Again you will not have the option of changing the number of pixels in the image. This selection results in the proportions of the image being fixed. If an image is 30 pixels wide and 60 pixels igh, no matter the size it is printed, the height will always be twice he size of the width. If the width value in the Document Size section is changed, both the height and the resolution values will also change. Change the height value and the width and resolution values will change. Change the resolution value, and the width and height values will change. They all work together as a function. The only change that can be made ow is how large or small the image will print. Simply entering new values for the document size or by changing the resolution will do this. The onstrain Proportions option is also not needed when all you are doing is resizing the print size of the image.

Constrain Proportions is grayed out when Resample Image is unchecked since you no longer have the option of changing the number of pixels in the image. This results in the proportions of the image being fixed. An image is 40 pixels wide and 20 pixels in height, regardless of how large or small it is printed, the width will always be twice the size of the height. If the width value in the Document Size section is changed, both the height and the resolution values will also change. Change the height value and the width and resolution values will change. Change the resolution value, and the width and height values will change. They all work together to adjust the image. The only change that can be made now is how large or small the image will print. You accomplish this by entering new values for the document size or by changing the resolution. The Constrain Proportions option is also not needed when all you are doing is resizing the print size of the image.

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.'

Time for the dictionary! "Bicubic" and "Bicubic Sharper" are what is called "iterpolation algorithms". Don't worry, simply put, this is what the Photoshop program does in regards to removed pixels when you resample the image to a smaller size, and how it handles added pixels when you resample the image to a larger size. Photoshop CS2 a third option called "Bicubic Smoother." Image quality can be compromised if you are unsure of which option to use when. Use these basic rules: Bicubic Sharper - Using this option when resampling your image smaller provides best image quality Bicubic Smoother - Using this option when resampling your image larger provides best image quality Bicubic - Typically not used as often being replaced with Bicubic Sharper and Bicubic Smoother

In professional terms, "Bicubic" and "Bicubic Sharper" are what is called "interpolation algorithms". Before you panic, this just refers to what the Photoshop program does to handle removed pixels when you resample the image to a smaller size, and how it handles adding pixels when you resample the image to a larger size. Photoshop CS2 a third option called "Bicubic Smoother." Image quality can be compromised if you are unsure of which option to use when. Use these basic rules: Bicubic Sharper - Using this option when resampling your image smaller provides best image quality Bicubic Smoother - Using this option when resampling your image larger provides best image quality Bicubic - Typically not used as often being replaced with Bicubic Sharper and Bicubic Smoother 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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