Resizing images is something you will always need to do as a photographer, so knowing how to do this precisely and for a range of reasons is something you will need to know.
Basic Pixel Resolution Sizing. The method you will be most used to using is Image/Image Size.
With width and height locked you would merely type in the resolution you require. If a client asks for an image no more than 2500 pixels on the longest side, with the width and height locked, you would merely type this in the Width section and the Height will be adjusted accordingly to keep the image aspect ratio the same.
With Width and Height unlocked then only entering one value will change the image shape, so always use it locked unless you have a specific need. One thing often overlooked when resizing are the resampling options. Depending upon whether you are increasing, or decreasing an image in size, these should be selected carefully.
Reduced to 1500 pixels across with Bilinear
Reduced to 1500 pixels across with Bicubic Sharper (Reduction)
When reducing, as you can see, using Bicubic Sharper adds a little sharpening to make the image appear sharper on screen.
Increased to 15000 pixels across using Bilinear .
Using Preserve Details keeps the image sharper when increasing the image size. When using Preserve Details, if the image is noisy, you can add noise reduction at this stage, but my advice is to do so sparingly or detail can be lost.
Resizing for printing.
When resizing for printing, it is important to also set the print resolution. Most commercial printers, assume you are using a file of 300 ppi (Pixels per inch). The files off your camera however may not be set to this. Many cameras (including the camera this test image was taken with) set 240ppi.
Using image/Image Size you can also resize the print resolution. More often than not though, you will want to size an image for a specific print size. For example, if we wanted to size this test image to print at A2, we’d need to set the actual print size at 300ppi and also set the print size to A2. You need to know the actual print size, and this can easily be found on the internet. A2 is 59.4 x 42cm Before you size, take note of the original pixel resolution, and set the width and height to Centimeters Then type in the dimensions you need.
Bear in mind, that almost certainly, the image will NOT be the same shape as an A2 page, so if it is a landscape image, set the width to 59.4. If a portrait image, set height to 59.4cm. THEN take note of how the pixel resolution changes…
As we can see the resolution has reduced, so we then need to choose the appropriate Resample method .
In this case, Bicubic Sharper, as we’re reducing pixel resolution. Our image is now 300ppi and will print exactly 59.4cm across. Resizing with the Crop Tool.
You can perform the same tasks with the crop tool.
Select the crop tool from the main toolbar.
Then on the context menu, select “W x H x Resolution”.
If you do not want to change the image shape, set width size only for a landscape image, and height only for a portrait image. And set 300ppi Bear in mind you have to actually type in the letters cm if you want centimeters.
You would then drag the cropping tool across the entire image (having snap turned on from the “view” menu helps here). Once the whole image is selected… double click to action the crop the image to the size and resolution set.
If you want your image to be exactly the same shape as the paper.. in this case A2 (59.4x 42cm) the crop tool is the ideal way to do it. Just set the exact paper size and 300ppi resolution.
As the image will not be the same size, you will need to decide how to crop it. Action the crop, and you will now have an image that will print exactly to A2. The problem with this method is that you cannot choose the resampling method. To get around this, you can crop to the required aspect ration first by setting the crop tool to “ratio”, and typing in the measurements you want… so for A2, you could type 5.94 x 42. No need to put cm etc, as it is a ratio. Crop… THEN use the Image/Image Size method. Then you can choose the resampling method.