Photoshop Tutorials Work...Resizing vs. Resampling

By: David Peters


Although there are those people who would argue, there is a difference between photo resizing and resampling even though both are Photoshop tools designed to change the size of an image. Many people make the mistake of using the two terms interchangeably: however the means by which resizing and resampling is performed is different. The key lies within how the image itself is altered. If this sounds confusing, have heartthe difference between to the two is just one simple checkbox away. Looking at the bottom of the Image Size dialog box, you will see a checkpoint option. This is the option that defines either the resizing or the resampling of the image.

By looking under the Image Menu at the top of the screen, you will find the Image Size dialog box. This option determines resizing or resampling. We mentioned the building blocks of an image before, these are called pixels. How the number of pixels is changed is the difference between resizing and resampling the image. Photoshop refers to this as changing the pixel dimensions. By keeping the number of pixels the same and only changing the size you wish the image to print is called resizing. In Photoshop speak this is termed as changing the document size of the picture. However, if you are actually changing the number of pixels making up the image, it is known as sampling.

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. Alright, now you know the definition of Image resizing and resampling. That's simple enough and don't worry because it really doesn't get much arder to do. You are only a step or two away from doing this with your own images

Resizing vs. Resizing An Image

Photoshop's Image Size dialog box contains some key pieces of information and is separated into two main parts. Pixel Dimensions make up the top half, while the Document Size portion is underneath. Pixel Dimensions shows the width and height consisting of the number of pixels the image is made up of. It also displays the file size of the picture. The Document Size part also shows width and height, but these are the dimensions at which the image will print. The image resolution, also found in the Document Size section of the Image Size box is what these numbers are based from. So remember, he Pixel Dimension will change how an image is displayed on your computer screen or even on the web, whereas changing the Document Size dimensions will affect the print size of the image. Pixel Dimensions = web Document Size = print

Before we begin, it is important to understand what information is contained in the Image Size dialog box. Photoshop's Image Size dialog box is divided into two main sections. The Pixel Dimensions section is on top, while the ocument Size section is below it. The Pixel Dimensions portion displays the width and height of the image in pixels, and also tells us the file size of our picture. The Document Size section tells how the width and height at which the image is going to print. This is based on the image resolution, also found in the Document Size section of the Image Size box. An easy rule of thumb is that the Pixel Dimension section is what you would change for displaying an image on the web or your computer screen. The Document Size is what you would use to change the dimensions at which the image will print. Pixel Dimensions = web Document Size = print

The Image Size box also contains a few more bits of information. You will find 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 will not distort. Resample Image - THIS IS WHAT YOU HAVE BEEN WAITING FOR!!!

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.

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.

Image Interpolation Options When Resampling Images

There is one more box that 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.'

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 your image will print (the Document Size). Image resampling - Physically changes the number of pixels in your image (the Pixel Dimensions). Resample Image - Option at the bottom of the Image Size dialog box controlling if you are resizing or resampling an image. Checking the Resample Image , 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 primarily 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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