Resizing vs. Resampling
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: 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
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
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 will touch a bit on Scale Style and Constrain Proportion, but it is that last box being checked or left blank that determines resizing vs. resampling. Remember that resizing keeps the pixel dimensions unchanged and only increases or decreases the size at which the image will print. Resampling however, actually changes the number of pixels in the image. The Resample Image option will be automatically checked by default. Basically, the dialog box still says ‘Image Size’ at the top, but its function now is as the Image Resample dialog box while being check marked. All options in both halves, the Pixel Dimensions and the Document Size, will be available to you.
If the Resample Image is unchecked, you will be able to view the number of pixels in both height and width in the Pixel Dimensions portion of the dialog box, but they are visible for information purpose only. You will not be able to change the values of the pixels. The only option available for change is the image print size 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.
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 also grayed out when Resample Image is unchecked. This is because there will not be the option of changing the number of pixels in the image either. This option results in the proportions of the image being fixed. An image is 100 pixels wide and 50 pixels in high, no matter the size 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 together. The only change that can be made now 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 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
Now comes some big words. “Bicubic” and “Bicubic Sharper” are what is called “interpolation algorithms”. All this boils down to is how the photoshop 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.