Specify DOM image conversion (#2805)

* Specify DOM image conversion

* Address feedback

Author: lexaknyazev

specs/latest/1.0/index.html

@@ -2602,8 +2602,55 @@ <h4>Texture objects</h4>
 
             The source image data is conceptually first converted to the data type and format
             specified by the <em>format</em> and <em>type</em> arguments, and then transferred to
-            the WebGL implementation. If a packed pixel format is specified which would imply loss
-            of bits of precision from the image data, this loss of precision must occur. <br><br>
+            the WebGL implementation. Format conversion is performed according to the following table.
+            If a packed pixel format is specified which would imply loss of bits of precision from the
+            image data, this loss of precision must occur. <br><br>
+
+            <table class="foo">
+              <tr>
+                <th rowspan="2">Source DOM Image Format</th>
+                <th colspan="5">Target WebGL Format</th>
+              </tr>
+              <tr>
+                <th>ALPHA</th>
+                <th>RGB</th>
+                <th>RGBA</th>
+                <th>LUMINANCE</th>
+                <th>LUMINANCE_ALPHA</th>
+              </tr>
+              <tr>
+                <td>Grayscale (1 channel)</td>
+                <td>A = 255 (1.0)</td>
+                <td>R = <em>sourceGray</em><br>G = <em>sourceGray</em><br>B = <em>sourceGray</em><br></td>
+                <td>R = <em>sourceGray</em><br>G = <em>sourceGray</em><br>B = <em>sourceGray</em><br>A = 255 (1.0)</td>
+                <td>L = <em>sourceGray</em></td>
+                <td>L = <em>sourceGray</em><br>A = 255 (1.0)</td>
+              </tr>
+              <tr>
+                <td>Grayscale + Alpha (2 channels)</td>
+                <td>A = <em>sourceAlpha</em></td>
+                <td>R = <em>sourceGray</em><br>G = <em>sourceGray</em><br>B = <em>sourceGray</em><br></td>
+                <td>R = <em>sourceGray</em><br>G = <em>sourceGray</em><br>B = <em>sourceGray</em><br>A = <em>sourceAlpha</em></td>
+                <td>L = <em>sourceGray</em><br></td>
+                <td>L = <em>sourceGray</em><br>A = <em>sourceAlpha</em></td>
+              </tr>
+              <tr>
+                <td>Color (3 channels)</td>
+                <td>A = 255 (1.0)</td>
+                <td>R = <em>sourceRed</em><br>G = <em>sourceGreen</em><br>B = <em>sourceBlue</em><br></td>
+                <td>R = <em>sourceRed</em><br>G = <em>sourceGreen</em><br>B = <em>sourceBlue</em><br>A = 255 (1.0)<br></td>
+                <td>L = <em>sourceRed</em></td>
+                <td>L = <em>sourceRed</em><br>A = 255 (1.0)</td>
+              </tr>
+              <tr>
+                <td>Color + Alpha (4 channels)</td>
+                <td>A = <em>sourceAlpha</em></td>
+                <td>R = <em>sourceRed</em><br>G = <em>sourceGreen</em><br>B = <em>sourceBlue</em></td>
+                <td>R = <em>sourceRed</em><br>G = <em>sourceGreen</em><br>B = <em>sourceBlue</em><br>A = <em>sourceAlpha</em></td>
+                <td>L = <em>sourceRed</em></td>
+                <td>L = <em>sourceRed</em><br>A = <em>sourceAlpha</em></td>
+              </tr>
+            </table><br>
 
             See <a href="#PIXEL_STORAGE_PARAMETERS">Pixel Storage Parameters</a> for WebGL-specific
             pixel storage parameters that affect the behavior of this function when it is called

specs/latest/2.0/index.html

@@ -1695,6 +1695,32 @@ <h4>Texture objects</h4>
       </dt>
       <dd>
         <p>Only differences from <a href="../1.0/index.html#TEXIMAGE2D_HTML">texImage2D</a> in WebGL 1.0 are described here. </p>
+        <p>Conversion to new formats introduced in WebGL 2.0 is performed according to the following table.</p>
+        <table class="foo">
+          <tr>
+            <th rowspan="2">Source DOM Image Format</th>
+            <th colspan="2">Target WebGL Format</th>
+          </tr>
+          <tr>
+            <th>RED</th>
+            <th>RG</th>
+          </tr>
+          <tr>
+            <td>Grayscale (1 channel)</td>
+            <td>R = <em>sourceGray</em><br></td>
+            <td>R = <em>sourceGray</em><br>G = 0</td>
+          </tr>
+          <tr>
+            <td>Grayscale + Alpha (2 channels)</td>
+            <td>R = <em>sourceGray</em><br></td>
+            <td>R = <em>sourceGray</em><br>G = <em>sourceAlpha</em></td>
+          </tr>
+          <tr>
+            <td>Color (3 channels)<br>Color + Alpha (4 channels)</td>
+            <td>R = <em>sourceRed</em><br></td>
+            <td>R = <em>sourceRed</em><br>G = <em>sourceGreen</em><br></td>
+          </tr>
+        </table><br>
         <p>Uploading subregions of elements is detailed in <a href="#DOM_UPLOAD_UNPACK_PARAMS">Pixel
            store parameters for uploads from <code>TexImageSource</code></a>.
         <p>If a WebGLBuffer is bound to the <code>PIXEL_UNPACK_BUFFER</code> target, generates an <code>INVALID_OPERATION</code> error.</p>