c# - WPF LayoutTransform (Scale) throws Exception because DesiredSize of Image is NaN -

i setting imagesource of image this:

stream imagestreamsource = new filestream(_filepath, filemode.open, fileaccess.read, fileshare.read); tiffbitmapdecoder decoder = new tiffbitmapdecoder(imagestreamsource,bitmapcreateoptions.preservepixelformat, bitmapcacheoption.onload); bitmapsource bmsrc = decoder.frames[0]; bmsrc.freeze(); imagesource = bmsrc; 

the image uses scaletransform (layouttransform) in scrollviewer.
layouttransform needed update scrollviewers content size.
want scale image size of parent of scrollviewer (bounds):

double horizontalaspectratio = gridbounds.width / image.width; double verticalaspectratio = gridbounds.height / image.height;  if (horizontalaspectratio > verticalaspectratio) {      scaletransformimage.scalex = scaletransformimage.scaley = verticalaspectratio;      messagebox.show("to height"); } else {      scaletransformimage.scalex = scaletransformimage.scaley = horizontalaspectratio;      messagebox.show("to width"); } 

after doing invalidoperationexception thrown , says measuring image's layout requires desiresize not nan.
tried measure , arrange image manually this:

image.measure(new size(double.positiveinfinity, double.positiveinfinity)); image.arrange(new rect(0d, 0d, gridbounds.width, gridbounds.height)); 

but doesn't seem have effect.
starting out transforms , not have lot of knowledge yet....

as long did not explicitly set image control's width , height properties, values nan, , aspect ratio calculation fail:

double horizontalaspectratio = gridbounds.width / image.width; double verticalaspectratio = gridbounds.height / image.height; 

you may instead use image's actualwidth , actualheight, or if not yet laid out, width , height of source:

double horizontalaspectratio = gridbounds.width / image.source.width; double verticalaspectratio = gridbounds.height / image.source.height;