Image size and resolution are important concepts in Photoshop. Understanding them helps you create images with the correct dimensions and quality for screens, websites, social media, and printing.
Image size refers to the dimensions of an image and, depending on the context, may also refer to the amount of storage space occupied by the image file.
In Photoshop, the pixel dimensions of an image are especially important for digital work.
Pixel dimensions describe the width and height of an image in pixels.
For example, an image that is 1920 × 1080 pixels contains 1920 pixels across its width and 1080 pixels down its height.
A pixel is a small individual unit of a raster image.
Millions of pixels can work together to form a complete photograph or graphic.
Pixel dimensions determine the amount of image information available for digital display.
Every raster image has a width and a height.
For example:
The first number normally represents width and the second represents height.
Width and height also determine the orientation of an image.
Resolution describes the density of pixels when an image is represented at a particular physical size.
Resolution is especially important when preparing images for printing.
In print workflows, resolution is commonly expressed in pixels per inch (PPI).
PPI stands for Pixels Per Inch.
It describes how many image pixels are represented within one inch of physical size.
PPI is primarily relevant when discussing the relationship between pixel dimensions and physical print dimensions.
PPI and DPI are related but are not exactly the same thing.
In Photoshop image settings, PPI is the more precise term for image resolution.
Photoshop provides an Image Size dialog for viewing and changing image dimensions and resolution.
You can access it through:
Image → Image Size
The Width field shows or controls the horizontal dimension of the image.
When working with digital images, width is often specified in pixels.
The Height field shows or controls the vertical dimension of the image.
Together, width and height determine the pixel dimensions of the image.
Resampling means changing the number of pixels in an image.
When you change the pixel dimensions of an image and resampling is enabled, Photoshop creates or removes pixels to produce the new dimensions.
Increasing pixel dimensions is called upscaling.
When an image is enlarged through resampling, Photoshop has to create additional pixels.
Increasing dimensions cannot always create the same detail as an originally high-resolution image.
Reducing pixel dimensions is called downscaling.
Downscaling can make an image smaller and can reduce the amount of storage or bandwidth required.
When resampling is disabled, changing the physical print size can change the resolution without changing the total number of pixels.
This is useful for understanding the relationship between pixel dimensions, physical size, and resolution.
Suppose an image is:
3000 × 2000 pixels
This means the image contains 3000 pixels across its width and 2000 pixels across its height.
Suppose an image has dimensions of:
3000 × 2000 pixels
If it is printed at 300 PPI, the approximate physical dimensions are:
10 × 6.67 inches
The same pixel dimensions can produce a different physical print size if a different PPI value is used.
Simply changing the resolution number does not automatically create new image detail.
When resampling is disabled, changing PPI changes the relationship between pixel dimensions and physical print size rather than creating additional pixels.
For screen-based work, pixel dimensions are usually more important than the PPI number.
Websites, mobile applications, social media platforms, and digital displays generally work with specified pixel dimensions.
For printing, pixel dimensions must be considered together with the intended physical print size.
A suitable resolution helps determine how densely the image pixels will be represented in the physical print.
Image dimensions and file size are not the same thing.
Image dimensions describe the width and height of the image, while file size describes how much storage space the file occupies.
File size can depend on dimensions, color information, compression, layers, and file format.
Larger pixel dimensions generally mean more image data needs to be stored, especially in uncompressed or minimally compressed formats.
A large PSD with many layers can also require significantly more storage space.
Higher pixel dimensions can provide more image information, but higher dimensions do not automatically guarantee a better looking image.
The quality of the original photograph, focus, lighting, compression, and other factors also matter.
Avoid increasing an image far beyond its original pixel dimensions unless there is a specific reason to do so.
Excessive enlargement can make an image appear soft or pixelated because additional pixels must be generated.
When creating social media graphics, first check the required dimensions of the target platform or design.
Create the Photoshop document using appropriate pixel dimensions so the final image fits the intended placement.
For print projects, determine the required physical dimensions first and then choose suitable pixel dimensions and resolution.
Always follow the specifications provided by the printing service when preparing professional print files.
Open a photograph in Photoshop and select:
Image → Image Size
Observe the following values:
The aspect ratio is the relationship between an image's width and height.
When resizing an image, maintaining the aspect ratio prevents the image from appearing stretched or squashed.
Always check the link or constrain-proportions option available in the current Photoshop version when resizing.
Image size and resolution are important when preparing images for digital display and printing.
Pixel dimensions describe the actual number of pixels in an image, while PPI describes pixel density in relation to physical print size.
In the next lesson, we will learn about Canvas Size and how it differs from Image Size.
Question: What does PPI stand for?