I don’t know how about you, but I always found it hard to understand everything related to image size. Pixel dimensions, aspect ratio, resolution… everything seemed difficult to me. However, I didn’t let myself get discouraged, and so my quest for knowledge began. I read a lot of articles and I watched quite a few tutorials and Lightroom courses. Today I want to share with you the useful things I’ve learned. Let’s start with some fundamental concepts and then we will move on to more complicated things like how to resize your images for both printing and web.
This is one of the most important concepts regarding photos. The pixel dimensions of your photo are telling you how many pixels your photo has. With Lightroom, you can know the pixel dimensions of your image by clicking “I” on your keyboard (when you have your image in Loupe mode, see image below). You will start a cycle of information overview in the photo. By clicking “I” once, you will see the file name, the date and time you took the photo and the pixel dimensions. When you click ‘I” again, you will see the settings of your photo (aperture, shutter speed..) and if you click “I” one last time, all the information disappear.
My photos, when taken straight from the camera, have a ratio of 3:2, meaning that images are 1.5 times wider than higher. This ratio is determined by the sensor of my camera. I have a Nikon D7000 and its sensor has a ratio 3:2, so my photos are 3:2 too. This ratio is common for sensors of both full frame SLRs and crop sensor cameras.
Other types of cameras have an aspect ratio of 4:3.
The aspect ratio affects the composition of your photos because it determines the frame size that will contain the elements of the image. Different frames might need different placement of the elements in order to get a pleasant photo.
You can change the aspect ratio of your photos in Lightroom using the cropping tool in the Develop module.
Lightroom’s cropping tool allows you to select from a variety of cropping ratios such as 1:1 (square format), 4×5, 5×7 and more.
When you crop an image, you reduce its pixel dimensions too.
The cropping tool also allows you to select just one section of your photo by clicking on selected parts of the cropping area (image below) and dragging until you get the element you want to the frame and place it as you want. You can readjust the position of your photo by clicking inside the cropping area (a little hand will appear in your cursor) and dragging the photo around.
Once you are happy with your cropping area, press enter or click the Done button and that’s all! Your photo is cropped! Notice again that after cropping an image its pixel dimensions change. What you will do by cropping in this way is resizing your image while keeping a particular aspect ratio.
Here is where things get complicated! The image resolution is the number of pixels you have in a certain space. It is usually measured in pixels per inch (PPI). So a 72ppi image will have 72 pixels in an inch, a 100ppi image will have 100 pixels in an inch and so on. In Lightroom, you set the resolution of your photo in the Export dialog. You can get to the Export Dialog by pressing “Export” in the Library module.
If you are a beginner and you don’t want to get into technicalities (I understand you because this can get really confusing!!), I can give you a rule for picking a resolution for your image. The first thing you should do is decide whether you want to print your photo or you want it to be used as a digital image.
If you are going to print your image, a good resolution is 300ppi. If you are going to print a canvas, a resolution of 150ppi is good enough. Take into account that the pixel dimensions of your photo together with your resolution will determine the size in inches/cm of your final printed photo. I will explain using an example:
I have a photo that has 3000 x 3000pixels. If I print it at 300 pixels by inch, doing the math (3000pixels divided by 300 pixels by inch) I get that my final print will be 10 x 10 inches. What happens if you don’t like this size…then you will need to resize it! I will tell you how in the following section.
It is more or less agreed that 72ppi is a good resolution for digital photos because this is the resolution of a lot of screens. There are screens with 100ppi and even 150ppi. But with digital images the important thing is how big your file will be (in MBs, that is). Higher resolution images weigh more Mb and this means that uploads and downloads to the web (social media, website or blog) will be slower. For that reason, it is usually accepted that a resolution of 72ppi is good for the web (perfect balance between good enough resolution for most screens and small enough files to make things fast on the web). If you prefer to use higher resolution images it will be at expenses of loading speed on your websites, so it is up to you to decide what is more important: higher resolution or faster loading speeds.
You might need to resize your image to a certain size of inches/cm (if you are printing them) or to certain pixel dimensions (if you are uploading your photos to social media or to your website, your images need to have certain dimensions). No problem! You can also do it in Lightroom (in the Export dialog).
Lightroom offers you several options for resizing your images. To keep it simple, today I am going to explain to you the one that I use for resizing almost all my images: resize to fit long edge.
When you mark the ” Resize to fit”, you will be able to open a bunch of options to resize your image. The one I use the most is the “Long edge”. Sometimes I will use also the “Short Edge” option.
Imagine that you want your final printed image to be 20 inches width. In the case of my rose photo, the width corresponds to the long edge of my photo because it is in landscape orientation. I keep the resolution in 300ppi because it is a good one for printing. I write 20 inches for the long edge and I select the units to inches. That’s all!! Now my image will be 20 inches wide and it will keep the 300ppi resolution!
For digital images, t works the same. Imagine that you want to post your photo in a Facebook album. In 2016, one of the sizes Facebook recommend is 2048pixels. In that case, you keep your resolution to 72ppi, the Long edge will be 2048 and the units should be “pixels”. Your photo is ready for Facebook!!
For resizing portrait oriented images you might find the “Resize to fit the short edge” useful because the short edge will determine the width of your photo.
That’s all for today!! Resizing images can get really complicated, but I wanted to keep it simple. Tell me if you find this article useful! Have a happy resizing!!