Today’s Question: Won’t resizing a picture to 1920 by 1080 pixels change the aspect ratio? Most pictures aren’t 16 by 9 natively.
Tim’s Quick Answer: This is a follow-up to a question about exporting photos from Lightroom for the purpose of presenting those photos on a television display. When you choose the option to resize photos when exporting from Lightroom, the aspect ratio of the photos will not be changed. That is because when you specify the “Width & Height” option in the Image Sizing section of the Export dialog you are only specifying the “container” you want the image to fit within. The image will not be stretched or cropped as part of this process.
More Detail: In some cases it is possible to alter the aspect ratio of a photo when you are resizing it. For example, in Photoshop you can use the Image Size command to resize an image. If you turn off the “lock” control (Constrain Proportions) then you can indeed change the aspect ratio of the photo.
In Lightroom, if you want to change the aspect ratio of a photo you need to use the crop tool. You can specify the aspect ratio you want to use from the Aspect popup, and then adjust the crop as needed. When you apply that crop, the aspect ratio of the image will obviously be altered. This would allow you to ensure that the image is resized to precise pixel dimensions for both the width and height, for example.
But when you use the Export command the existing crop (and thus the existing aspect ratio) will be preserved. Resizing the image will cause the image to be resized within the constraints you’ve defined, but without altering the aspect ratio. In other words, the final pixel dimensions for the image may be somewhat different (in one dimension) from what you entered in the Image Sizing section of the Export dialog.