Photography Basics: Image File Types, Size and Resolution Explained

One of the features of digital cameras that newcomers often overlook is the ability to change file types on their camera. When you take a photo on your camera, the resulting picture is stored digitally on either a memory card or on your camera. There are a variety of digital file types that the camera uses, and some have particular uses or benefits over others. You need to consider not only how the image is stored, but how easy it is to edit afterwards, and what it will look like when printed. This article will give you the basics of image file types and how to convert between them. We’ll also cover image size and resolution and how it affects the image for both print and screen.

Image File Types

Raster (Lossy) vs Vector (Lossless) Images

There are two categories of image file available, each with their own unique characteristics and various formats. Understanding how each works is important for processing the images you take with your digital camera.

Your digital camera will take raster images, and we’ll explore the different raster formats further on. Essentially raster images are created with pixels. When you hear the term ‘megapixel’ in relation to your camera, the number and density of these will determine the resolution. Raster images can be used for both simple and complex images, but one of the issues they face is that they don’t scale up well. Increasing the size of a raster image will often result in a loss of quality. That’s why it’s often the final version of an image.

Vector images work differently. Rather than a collection of data in pixels, the data instead takes the form of mathematical formulae. The formula of a vector image informs the computer of what shapes to render. This makes them easily resized. However, although vectors are useful for illustrations, logos and text, they’re not suitable for capturing photos.

Raster Formats

Below are some of the raster formats available, with a little information about each:

  • JPEG: JPEGs are incredibly popular thanks to their small size and lossy compression. It makes it possible to store a lot of them on a memory card and is often used in web design thanks to their fast load speeds. However, they’re not particularly well suited to print or logos due to their lack of quality.
  • GIF: GIF stands for Graphics Interchange Format and it’s a file type that’s popular in web design. One of the main benefits of GIF files is that they can be animated. They can also have transparent backgrounds and quite low file sizes.
  • PNG: PNG files combine the best parts of JPEGs and GIFs; they’re great for high-quality photographs, and can have transparent backgrounds, making them a good choice for web design. However, file sizes can be pretty big which isn’t ideal for loading times.
  • TIFF: TIFF is a lossless file format, meaning it can be resized or compressed without losing quality. They can also support layers. This is another type that has a large file size, however.
  • PSD: PSD files are native to Photoshop and can be layered and adjusted without a loss of quality.

Vector Formats

Some notable vector formats include:

  • EPS: EPS is a standard vector format that uses formulae to create an illustration. It’s great for any format that needs to be resized, such as a logo.
  • AI: AI is very similar to EPS, except it is Adobe’s own file type. Programs such as Adobe Illustrator will save files in this format.

Converting Between Different File Types

As a photographer it’s likely that you’ll encounter a variety of file types and want to convert between them. As we’ve mentioned, different types are suitable for different purposes. So, how do you convert between file types? You can use editing software such as Photoshop or Lightroom to save between different file types. Programs such as this will often give you the option as to what kind of format you want to output in. However, be aware that if you save a high-resolution image in a low-resolution file type, you will lose quality in that image.  As well as editing software, it’s possible to find free file converters online.

Image Size and Resolution

Image quality is directly linked to the size and resolution of the image. Digital images are comprised of millions of individual pixels (blocks of color) that combine to create a smooth and clear picture. The more pixels there are the better quality the image. This is because the greater the number of pixels, the more detail the image can capture.

Although from a distance it may be hard to tell the difference in pixels, it’s important to remember than when you zoom in, crop, or print a photo that you’ve taken, the quality will be more noticeable. When you’re choosing a camera, quite often you’ll see the megapixel rating of the sensor. Along with the size of the sensor (Full-frame, APS-C, four-thirds), the number of megapixels will determine the resolution and therefore the quality.

When you’re editing your photos in post-production, you will be able to change three separate factors. Along with the resolution in pixels, you can also change the height and width of the picture. Often, by changing one the others will change automatically so that your image scales correctly.

Why Size Is Important When Printing

The megapixel rating of your camera roughly equates to the number x 1,000,000. So for example, a 24-megapxiel sensor will produce images with 24 x 1,000,000 pixels, or 24,000,000 pixels. Most crop-frame cameras will have an aspect ratio of 1.5 and when you compare this to the ratio of pixels along the long and short sides of the image, you get 3:2. These numbers are important when it comes to printing your photos.

Resolution is important when printing, as is the ppi, or pixels per inch. For the best clarity, you’ll want to try and achieve around 150-300 ppi, although professional shots can reach up to 1200 ppi. So to work out how many pixels you’ll need, you have to do some basic math. For example, if you want to print out a photo in 8 x 10 inches at 300 ppi, you’ll need 8×300 pixels on the short side, and 10×300 pixels along the long side. In total, this is 2400 x 3000 pixels. You’ll need to bear this in mind when cropping and resizing your images; if the number of pixels is too low, the quality of your prints will be noticeably affected.

Sizing for Screens

One of the benefits of displaying your work on a screen is that often the resolution isn’t that high. Full HD screens can only output in 1920×1080 pixels, whilst newer 4K screens are capable of 3840 × 2160 pixels or 8.3 megapixels with an aspect ratio 16:9. This means that the resolution doesn’t have to be as high as for printing. A 1920 x 1080 display is roughly equivalent to a 4 x 6 inch print at 300 ppi.

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