title: Pretrained Tensorflow model RGB -> RGBY channel extension
body: <p>I am working on the <a href="https://www.kaggle.com/c/human-protein-atlas-image-classification/data" rel="nofollow noreferrer">protein analysis project</a>. We receive the <a href="https://www.kaggleusercontent.com/kf/7215060/eyJhbGciOiJkaXIiLCJlbmMiOiJBMTI4Q0JDLUhTMjU2In0..LPZ9_xvlaqTrcG2SKlup1g.cLeDCrM3KtoP5P8ST0YZ92L0LYO9Jkg4HH0-kcrOivqGrs3nn35sgxLIMGVabuY6d-DNJ8qhHukxM8kEqFz3qP_kcC2mE-sxsywBuKsXTVg9EmHSddJT_4U_zAg4-ZUPS23LLUI4Gid5baxgWNGjmmsExp6wjs_uBbZJowwKfps.kxXJmjlVMWA1ROgOiCcKLg/__results___files/__results___54_0.png" rel="nofollow noreferrer">images</a>* of proteins with 4 filters (Red, Green, Blue and Yellow). Every of those RGBY channels contains unique data as different cellular structures are visible with different filters. </p>
  
  <p>The idea is to use a pre-trained network e.g. VGG19 and extend the number of channels from default 3 to 4. Something like this:</p>
  
  <p><em>(My appologies, I am not allowed to add images directly before 10 reputation, please press the "Run code snippet" button to visualize):</em>
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;img src="https://i.stack.imgur.com/TZKka.png" alt="Italian Trulli"&gt;</code></pre>
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  <p><em>Picture: VGG model with RGB extended to RGBY</em></p>
  
  <p>The Y channel should be the copy of the existing pretrained channel. Then it is possible to make use of the pretrained weights. </p>
  
  <p>Does anyone have an idea of how such extension of a pretrained network can be achieved?</p>
  
  <p>*
  <em>Author of the collage - Allunia from Kaggle, "Protein Atlas - Exploration and Baseline" kernel.</em></p>