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    <p>According to the <a href="http://www.w3.org/Graphics/GIF/spec-gif89a.txt" rel="noreferrer">GIF spec</a>, the byte stream of a gif image starts with 6 bytes for the header, and 7 bytes for the "logical screen descriptor".</p> <p>The 5th byte of the logical screen descriptor is a "packed fields" byte. The first bit of the "packed fields" is set if the image contains a global color table. The last three bits are a number X that you can use to calculate the size of the global color table as <code>3 x 2^(X+1)</code>.</p> <p>Then follows the global color table (if it is present). To skip over this you need to know its size, calculated as shown above.</p> <p>Then follows a 10 byte "image descriptor". The last byte of those is another "packed fields". <strong>The second bit of that byte is set if the image is interlaced.</strong></p> <pre><code> public bool IsInterlacedGif(Stream stream) { byte[] buffer = new byte[10]; int read; // read header // TODO: check that it starts with GIF, known version, 6 bytes read read = stream.Read(buffer, 0, 6); // read logical screen descriptor // TODO: check that 7 bytes were read read = stream.Read(buffer, 0, 7); byte packed1 = buffer[4]; bool hasGlobalColorTable = ((packed1 &amp; 0x80) != 0); // extract 1st bit // skip over global color table if (hasGlobalColorTable) { byte x = (byte)(packed1 &amp; 0x07); // extract 3 last bits int globalColorTableSize = 3 * 1 &lt;&lt; (x + 1); stream.Seek(globalColorTableSize, SeekOrigin.Current); } // read image descriptor // TODO: check that 10 bytes were read read = stream.Read(buffer, 0, 10); byte packed2 = buffer[9]; return ((packed2 &amp; 0x40) != 0); // extract second bit } </code></pre> <p>No doubt a similar inspection of the byte stream can be done for JPG and PNG, if you read those specifications.</p>
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    1. POIn C#, how do I determine if an image (jpg, gif, or png) is interlaced (non-progressive) or non-interlaced (progressive)?
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    1. USWim Coenen
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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