Save image from bitmap to jpeg without save the file

I have a problem that I need to have a jpeg image with dpi 500 first it come from base64 I could converted it directly to jpeg but I don't know how to set the dpi to system.drawing.image

I have a solution is to get the image as bitmap then use the setresolution function to reset it to 500*500 and that what I need but to reconvert the bitmap again to jpeg it needs to be saved on physical drive and also I couldn't do that

so I just need to get from image or bitmap to jpeg with 500*500 resloution actually I also will read it again to开发者_如何学运维 array of bytes but I need this array from a jpeg image with 500*500 dpi and the converted image from base64 is not 500*500 dpi

any idea will be appreciated

The Image class is abstract, so you can't have an instance of that class. What you have is really an instance of the Bitmap class, but a reference to that with the type Image.

So, you just have to cast the reference to the actual class of the object, and you can access its methods:

((Bitmap)theImage).SetResolution(500, 500);

Seems you have some misunderstanding what dpi means. 500 means that each inch of an object in an image is represented using 500 pixels. So, dpi isn't really a characteristic of an abstract image. It's a characteristic of how a real object is represented with an image. That means you don't need to change image's resolution at all.