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POHow to display Grayscale image after changing the indexing in C#
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  1. POHow to display Grayscale image after changing the indexing in C#
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    copied!<p>I have a Grayscale image which I am pulling from the DB (it is in Bytes). I want to draw some boxes using graphics object on it and then display this image. This is what was coded before -</p> <pre><code>public byte[] DrawOverlayOnGreyscaleImage(byte[] buffer, List&lt;ImagingTransaction.ImagingTransactionField&gt; TransactionFieldList, BLLImageType imageType) { //Load image into a bitmap object via first going into a MemoryStream MemoryStream msBitmap = new MemoryStream(buffer); Bitmap BitmapObj = null; BitmapObj = new Bitmap(msBitmap); int bmwidth = BitmapObj.Width; int bmheight = BitmapObj.Height; // draw some text on top Graphics g = Graphics.FromImage(BitmapObj); </code></pre> <p>Because of the changes in the way the image is now generated (Format8bppIndexed) the Graphics object threw an exception - "A graphics object cannot be created from an image that has an indexed pixel format". So I changed the Bitmap to be Format24bppRGB. Now, there is no exception. But after I draw boxes on the image and try to save it, the image is all black. This is because in case of "Grayscale" images R=G=B. This is lost after making it non indexed. I change the Bitmap to be again Indexed (Format8bbIndexed). Change the ColorPalette, but nothing helps. I still get the image to be totally black. Please help. My new code is as follows -</p> <pre><code>public byte[] DrawOverlayOnGreyscaleImage(byte[] buffer, List&lt;ImagingTransaction.ImagingTransactionField&gt; TransactionFieldList, BLLImageType imageType) { //Load image into a bitmap object via first going into a MemoryStream MemoryStream msBitmap = new MemoryStream(buffer); Bitmap BitmapObj = null; BitmapObj = new Bitmap(msBitmap); int bmwidth = BitmapObj.Width; int bmheight = BitmapObj.Height; Bitmap tmp = new Bitmap(BitmapObj.Width, BitmapObj.Height, System.Drawing.Imaging.PixelFormat.Format24bppRgb); Graphics g = Graphics.FromImage(tmp); Rectangle srcRect; int RectWidth; int RectHeight; Pen myPen = new Pen(System.Drawing.Color.Red, 3); foreach (ImagingTransaction.ImagingTransactionField Field in TransactionFieldList) { // first, do they want to see the rectangles if (imageType == BLLImageType.GreyScale_With_FieldRectangles || imageType == BLLImageType.GreyScale_With_FieldRectangles_And_Field_Data) { RectWidth = Field.LowerRightX - Field.UpperLeftX; RectHeight = Field.LowerRightY - Field.UpperLeftY; // sanity check for negative values if (RectWidth &lt;= 0) RectWidth = 10; if (RectHeight &lt;= 0) RectHeight = 10; srcRect = new Rectangle(Field.UpperLeftX, Field.UpperLeftY, RectWidth, RectHeight); g.DrawRectangle(myPen, srcRect); } // now, do they want to see the text to the lower right of the field if (imageType == BLLImageType.GreyScale_With_Field_Data || imageType == BLLImageType.GreyScale_With_FieldRectangles_And_Field_Data) { g.DrawString(Field.FieldValue, new Font("Tahoma", 12), Brushes.Red, new PointF(Field.LowerRightX, Field.LowerRightY)); ; } } MemoryStream msBitmapWithRectangle = new MemoryStream(); // Save to memory using the Jpeg format Bitmap tmp2 = new Bitmap(tmp.Width, tmp.Height, System.Drawing.Imaging.PixelFormat.Format8bppIndexed); ColorPalette pal = tmp2.Palette; for (int i = 0; i &lt; pal.Entries.Length; i++) { // create greyscale color table pal.Entries[i] = Color.FromArgb(i, i, i); } tmp2.Palette = pal; tmp2.Save(msBitmapWithRectangle, System.Drawing.Imaging.ImageFormat.Jpeg); // read to end byte[] ByteArrayWithRectangle = msBitmapWithRectangle.GetBuffer(); // cleanup tmp.Dispose(); tmp2.Dispose(); BitmapObj.Dispose(); msBitmap.Close(); msBitmapWithRectangle.Close(); return ByteArrayWithRectangle; } </code></pre>
 

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