subject: Difference Between Photo Resizing and Resampling - Resizing vs. Resampling An Image [print this page] Difference Between Photo Resizing and Resampling - Resizing vs. Resampling An Image
Learn Photoshop Now... 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. 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. Resampling 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
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.
The Scale Styles and Constrain Proportions options at the bottom of the Image Size dialog box may or may not be grayed out. When 'Resample Image' is unchecked, you will not have access to these options. Scale Styles is grayed out because it's only used when the number of pixels in an image is being changed. With the number of pixels in the image remaining the same when Resample Image is blank, the Scale Styles is not necessary.
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
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.'
Now comes some big words. "Bicubic" and "Bicubic Sharper" are what is called "interpolation algorithms". All this boils down to is how the hotoshop program handles removing 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. In Photoshop CS2, there is another option added called "Bicubic Smoother." Knowing when to use which option can make a big difference with image quality, but can be remembered with a basic rule as follows: Bicubic Sharper - Use this option when resampling your image smaller for best image quality Bicubic Smoother - Use this option when resampling your image larger for best image quality Bicubic - Not used as much with Bicubic Sharper and Bicubic Smoother being available These options will be grayed out here because they only apply to 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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