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Get Photoshop...Resizing vs. Resampling

May 3, 2008
Contrary to what you may think, there is a difference between photo resizing and resampling although both are tools used to change the size of an image in Photoshop. Many people might believe the two terms are basically interchangeable; however how the result is accomplished is different in how it changes the building blocks of the image itself. Although this may sound drastic, the difference between to the two is all in one simple click. At the bottom of the Image Size dialog box, there is a checkpoint option that creates either the resizing or 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.

Resizing vs. Resizing An Image

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!!!

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 notice 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 unchecked. Scale Styles is grayed out because it's only used when the number of pixels in an image is being changed. Since the number of pixels in the image remains the same with Resample Image left blank, the Scale Styles is not needed.

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

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

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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