title: (Py)Vips vs Pillow upscaling image quality
body: <p>Resizing an image to 200% yields a difference in quality between Pillow and pyvips.  </p>
  
  <p>While Pillow is very accurate in the reproduction, vips exaggerates noise and contrast.</p>
  
  <p>I need to use vips for very large images, but the quality is unsatisfactory. Any idea how to get better upscaling from vips? (From the docs I gathered that upscaling isn't really that important for vips and most thought has gone into downscaling).</p>
  
  <p>example:</p>
  
  <pre><code>from PIL import Image
  import pyvips
  import numpy as np
  
  #Vips
  img = pyvips.Image.new_from_file("mypic.jpg", access='sequential')
  out = img.resize(2, kernel = "linear")
  out.write_to_file("mypic_vips_resized.tif")
  
  #Pillow
  img = np.array(Image.open("mypic.jpg"))
  h, w = img.shape[:2]
  out = Image.fromarray(img,mode="RGB")
  out = out.resize((w*2,h*2), Image.BILINEAR)
  out.save("mypic_PIL_resized.tif", format='TIFF', compression='None')
  </code></pre>
  
  <p>Original:<br>
  <a href="https://i.stack.imgur.com/F6XYP.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/F6XYP.jpg" alt="original"></a><br>
  Pillow:<br>
  <a href="https://i.stack.imgur.com/n66Ud.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/n66Ud.jpg" alt="Pillow"></a><br>
  Vips:<br>
  <a href="https://i.stack.imgur.com/FPjpU.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/FPjpU.jpg" alt="Vips"></a></p>
  
  <p>Abstract examples (10*10 Pixels)  </p>
  
  <p>Original:<br>
  <a href="https://i.stack.imgur.com/cGm1T.png" rel="noreferrer"><img src="https://i.stack.imgur.com/cGm1T.png" alt="Original"></a><br>
  Pillow Bilinear:<br>
  <a href="https://i.stack.imgur.com/nH8FO.png" rel="noreferrer"><img src="https://i.stack.imgur.com/nH8FO.png" alt="Pillow Bilinear"></a><br>
  Vips linear:<br>
  <a href="https://i.stack.imgur.com/VlFfm.png" rel="noreferrer"><img src="https://i.stack.imgur.com/VlFfm.png" alt="Vips linear"></a></p>