C# – Get aspect ratio (width and height) of an uploaded image

asp.net-core-2.0asp.net-core-webapic

I want to validate my image upload in my API. I want only allow photos which are in landscape mode. I would also like to check the aspect ratio. This is my code for checking if the iFormFile is an image:

    [HttpPost]
    public JsonResult Post(IFormFile file)
    {
        if (file.ContentType.ToLower() != "image/jpeg" &&
            file.ContentType.ToLower() != "image/jpg" &&
            file.ContentType.ToLower() != "image/png")
        {
            // not a .jpg or .png file
            return new JsonResult(new
            {
                success = false
            });
        }

        // todo: check aspect ratio for landscape mode

        return new JsonResult(new
        {
            success = true
        });
    }

Since System.Drawing.Image is not available anymore, I couldn't find a way to convert the iFormFile into an Image typed object, to check the width and height to calculate the aspect ratio of it. How can I get the width and height of an image with the type iFormFile in ASP.NET Core API 2.0?

Best Answer

Since System.Drawing.Image is not available anymore, I couldn't find a way to convert the iFormFile into an Image typed object, to check the width and height to calculate the aspect ratio of it.

That's actually not correct. Microsoft has released System.Drawing.Common as a NuGet, which provides cross-platform GDI+ graphics functionality. The API should be an in-place replacement for any old System.Drawing code:

using (var image = Image.FromStream(file.OpenReadStream()))
{
    // use image.Width and image.Height
}

Related Solutions

C# – How to get the file size of a “System.Drawing.Image”

If you get your image directly from file, you can use the following code to get size of original file in bytes.

 var fileLength = new FileInfo(filePath).Length;

If you get your image from other source, like getting one bitmap and composing it with other image, like adding watermark you will have to calculate size in run-time. You can't just use original file size, because compressing may lead to different size of output data after modification. In this case, you can use MemoryStream to save image to:

long jpegByteSize;
using (var ms = new MemoryStream(estimatedLength)) // estimatedLength can be original fileLength
{
    image.Save(ms, ImageFormat.Jpeg); // save image to stream in Jpeg format
    jpegByteSize = ms.Length;
 }

C# – Resize Image to fit in bounding box

Find which is smaller: MaxWidth / w or MaxHeight / h Then multiply w and h by that number

Explanation:

You need to find the scaling factor which makes the image fit.

To find the scaling factor, s, for the width, then s must be such that: s * w = MaxWidth. Therefore, the scaling factor is MaxWidth / w.

Similarly for height.

The one that requires the most scaling (smaller s) is the factor by which you must scale the whole image.

Best Answer

Related Solutions

C# – How to get the file size of a “System.Drawing.Image”

C# – Resize Image to fit in bounding box

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