Whenever we take a picture with our camera, the resolution of the photo can be very high for uploading to the web, so we need to down-sizing it to suit our needs. Some websites reduce the resolution and image quality automatically, but the process is not really accurate, so it’s better to do it for ourselves to get greater results. To know how to adjust the size of an image in post-processing is essential and very easy to learn.
There are two methods to modify the size of our picture. We can either resize or resample them, and it’s really important that they are not the same thing!
- Resizing means that we alter the size of an image without changing the number of pixels in it.
- Resampling refers to modifying the amount of pixels in a photo. As a result, when we need to decrease the image size, we call it down-sampling and if we need to increase the number of pixels in our picture it’s called up-sampling. However, when we are up-sampling our images the outcome won’t be excellent, as during the processing method the image loses its details and sharpness.
These expressions can be a bit confusing but I think it’s important to know what is the difference between them and call the method we use correctly. Let’s have a look more closely how to down-sample our images.
First, we need to open up the image in Photoshop. Then go to Image at the top of the window and choose Image size from the list. Now we should see the image size dialog box on the screen.
As indicated the image size is 7MB and the dimensions are 1920×1280 pixels. If we need a smaller version, then
- we either have to change the values in the width and height boxes
- or simply decrease the resolution of the image.
If we know what size we need, then it makes sense to follow the first procedure.
We might need to change units from the drop-down list, make sure they are measured in Pixels. Then simply modify the values in the Width and Height boxes.
I use Photoshop 2019, but in case you have an older version you might need to click on Constrain Proportions in the image size dialog box, if you wish to change the width of the image. This case Photoshop will change automatically the height and other way round, so the proportions won’t get deformed. However, if we wish to change both the height and width individually, we don’t need to tick the box.
Very briefly, for web or screen use it’s recommended to adjust the resolution to 72ppi (pixels per inch), while the standard size for prints is 300ppi.
Make sure that the resample option is ticked, which means the width and height of the picture will change, that’s what we called resampling. However, if the resample option is unticked, it means we are going to resize the image! So basically if the box is ticked we are going to resample the image, and if it isn’t then to resize it. It’s that simple!
We can select different interpolation algorithms when down-sampling our images. Interpolation means Photoshop analyses the colours of the original pixels and creates new ones or eliminate some of the existing ones, depending on the sampling method what we use.
There are different alternatives to choose from:
- Automatic -This method chooses the best algorithm based on the document type and whether it’s scaling up or down.
- Preserve details – This interpolation method is mainly used when up-sampling images. It has an additional noise reduction slider which is a handy tool to reduce the unwanted noise.
- Bicubic Smoother – A good method when we need to up-sample our images but please aware that results are not accurate, it can affect the sharpness.
- Bicubic Sharper – A good method for down-sampling images with improved sharpening.
- Bicubic Smoother Gradients – A slower but more precise method which decreases the image dimensions only, without adding any sharpening to the photo. This method uses more complex estimates and details are well maintained.
- Nearest Neighbour – A fast but not very accurate method that preserves hard edges in an image, and because of this, we don’t have to do any sharpening. The photo looks crisp after down-sizing the original file. Also worth knowing, that unfortunately, this method doesn’t function properly for more precise details, so it isn’t the best choice for photographs.
- Bilinear – this option is very similar to Bicubic Smooth Gradients. Recommended when down-sampling images.
And there we have it! I hope this article was useful and easy to understand! Thanks for reading it!