I am switching an existing MVC 4 website from home-cooked user file uploads to resizing files with ImageResizer as they are uploaded.
I see in the documentation that I should not use System.Drawing, but I can't figure out any other way of grabbing the image dimensions.
It does not matter if the dimensions are from the original image or a resized image, since I am preserving aspect ratio and merely need to determine if an image is landscape or portrait.
I am adding the code here that I refer to in my comment responding to @Nathanael's answer.
ImageJob ij = new ImageJob(file, requestedImageInfo: null);
int ? y = ij.SourceWidth;
int ? z = ij.SourceHeight;
If you can store the image dimensions during upload (from ImageJob.SourceWidth/Height or LoadImageInfo), that is best, as reading image dimensions from a file involves lots of I/O.
If not, ImageResizer offers the IDictionary LoadImageInfo(object source, IEnumerable requestedInfo) method to do so after the fact. Just keep in mind, it does involve reading from disk, and you don't want to call this lots of times in a single HTTP request. Put those numbers in the database.
You can always calculate the final size of an image via ImageBuilder.GetFinalSize(originalSize, instructions). This, on the other hand, is very fast, as it involves no I/O, just math.