The post Understanding Pixels and Resolution (+ How to Resize Images in Photoshop) appeared first on Digital Photography School. It was authored by Ana Mireles.
Do you buy your camera based on its megapixel count? Have you encountered problems sharing your photos online due to large file sizes? Do your prints appear low quality even though they look stunning on your screen?
These are common issues that arise from confusion between pixels and bytes, image size and file size, and the like. In today’s digital age, understanding the nuances of image size, resolution, and file formats is essential for anyone dealing with photos, whether you’re a seasoned professional or a casual hobbyist.
I want to emphasize that mastering these concepts is not just about gaining technical knowledge; it’s about improving your workflow and ensuring your images are optimized for their intended use. Whether you’re uploading photos to social media, printing large-format posters, or simply organizing your digital photo library, understanding the basics of pixels and resolution will make your tasks easier and more efficient.
So let me explain how to make your life simpler, your workflow more effective, and your images the correct size for the intended usage!
Is resolution the same as size?
One of the biggest misunderstandings comes from the concept of resolution. If it’s something you struggle with, believe me, you’re not alone.
The problem is that resolution can refer to many things, two of which relate to the problem at hand. I’ll explain these two resolution concepts further, but they have one thing in common that I need to clarify first: They both have to do with pixels.
You’ve probably heard a lot about pixels, at least when you bought your camera. It’s one of the most advertised and valued specs on the market, so I’ll start there.
What is a pixel?
A digital photo is not one indivisible entity. If you zoom in far enough, you’ll see that your image is like a mosaic formed by small tiles, which in photography are called pixels.
The number of these pixels and the way they are distributed are the two factors you need to consider to understand resolution.
Pixel count
The first kind of resolution refers to the pixel count, which is the number of pixels that form your photo.
To calculate this resolution, you use the same formula you would for the area of any rectangle: multiply the length by the height.
For example, if you have a photo with 4,500 pixels on the horizontal side and 3,000 on the vertical side, multiply those two numbers to reach a total of 13,500,000 pixels.
Because this number is impractical to use, you can divide it by a million to convert it into megapixels. So 13,500,000/1,000,000=13.5 megapixels.
Pixel density
The other kind of resolution is about how you distribute the total amount of pixels you have. This is commonly referred to as pixel density.
Resolution is expressed in dpi (dots per inch) or ppi (pixels per inch). If you come across an image with 72 dpi, it means that the image has 72 dots per inch; if you see an image displayed at 300 ppi, it means the image has 300 pixels per inch.
The final size of your image depends on the resolution you choose. If an image is 4500×3000 pixels, it will print at 15×10 inches if you set the resolution to 300 dpi, but it will print at 62.5 x 41.6 inches at 72 dpi.
Here, while the size of your print changes, you are not resizing your image file; you are just redistributing the existing pixels across the space.
Imagine a rubber band; you can stretch it or shrink it, but you’re not changing the composition of the band. You’re not adding or cutting any of the rubber.
To summarize: resolution is not the same as size, but they are related.
Does quantity equal quality?
Because of the correlation between size and resolution, many people think that more megapixels result in higher-quality files.
In a sense, this is true; the more pixels you have, the higher the pixel density will be for a given area.
However, you should also consider the depth of the pixels, which determines the number of tonal values in your image. This depth translates to the number of colors per pixel. For example, a 2-bit depth pixel can store only black, white, and two shades of grey. More commonly, 8-bit depth pixels are used.
The values grow exponentially, so with an 8-bit photo (2^8=256), you’ll have 256 tones of green, 256 tones of blue, and 256 tones of red, amounting to about 16 million colors.
This is already more than the eye can distinguish, meaning that 16-bit or 32-bit images will look relatively similar to us. However, a higher bit depth makes your image file heavier, even if the size is the same, because each pixel contains more information. This is why quality and quantity are not necessarily the same.
Quantity helps, but the size and depth of each pixel also determine quality. This is why you should consider all the specs of a camera and its sensor, not just the number of megapixels. After all, there’s a limit to the size you can print or view your image; beyond that, you’ll only increase the file size (megabytes) without improving the image size (megapixels) or quality.
How to choose and control image size and file size
First, you need to consider where your photo will be displayed. The image output will dramatically affect the ideal image size.
For instance, newspapers are often printed at 72 dpi; therefore, if your image will be displayed in a newspaper, it often makes sense to send a file with 72 dpi. (The exception is when the paper uses a higher dpi count, in which case you should increase the image size accordingly!)
This is too low for fine-art printing, however – for “proper” prints, you generally need 300 dpi for high-quality results. Again, however, this depends on the printer in question; some printers can print at much higher dpi, while others are limited to a lower density.
You should also think about the way the image will ultimately be viewed. A 200 dpi print might look bad when viewed up close at 8×10, but at 40×60, the viewer will likely be standing farther away, and 200 dpi will look great!
Once you’ve determined the ideal density, you can calculate the necessary image dimensions for a specific print size. For example, if you want to print your photo at 8×10 inches, you need your image to have 300 dpi x 8″ = 2400 pixels by 300 dpi x 10″ = 3000 pixels (so 2400×3000 pixels to print an 8×10 at 300 dpi).
How to resize an image in Photoshop
Now it’s time to cover the practical stuff: actually resizing your images in Photoshop to match your desired output.
Start by opening the Image option in the main menu. Select Image Size, and in the popup window, tick the Resample Image box. (If you don’t activate resampling, you will only be redistributing the pixels, as explained earlier.)
At the top of the window, you’ll also see how the file size changes. This uncompressed version of your image directly relates to what was explained earlier: fewer pixels mean less information.
If you still want to change the file size without resizing, you need to do so when you save the image. Before saving, you can choose the format:
If you don’t want to lose any information, save in an uncompressed format. The most common and easiest to share is TIFF.
If you don’t mind losing some information for a lighter file, opt for JPEG and choose the desired compression level. The smaller you set it, the more information you lose. Fortunately, there’s a preview button to see the impact of your compression.
Print and resize your photos with confidence!
Understanding the intricacies of image quality, quantity, size, and resolution is crucial for anyone working with digital photos, whether for professional purposes or personal enjoyment. Pixels, the fundamental building blocks of digital images, play a pivotal role in determining these factors. By grasping how pixel count and pixel density interact, you can make informed decisions about your images, ensuring they meet your needs for both digital and print formats.
Now that you have a comprehensive understanding of these elements, you are well-equipped to make the best choices for printing, sharing, and saving your photos. Whether you are a professional photographer, a hobbyist, or someone who simply enjoys capturing moments, this knowledge will empower you to achieve the best possible results with your digital images!
Now over to you:
Do you struggle to understand these concepts? Do you have any tips or advice for others? Share your thoughts in the comments below!
The post Understanding Pixels and Resolution (+ How to Resize Images in Photoshop) appeared first on Digital Photography School. It was authored by Ana Mireles.
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