A Graphics object cannot be created from an image that has an indexed pixel format.

Question

User1090916182 posted

Hi

I'm really struggling to create a method that resizes JPG/GIF images then saves them back out.  I've Google'd the error now for 2 days but can't find a solution that I can get working.  I know this is a really common error so am hoping somebody can show me the code to get this working, which will help others in the future.

Basically I need to load an image from a file, then resize it to some pre-determined size, then save it back in the original format.  I get an Exception however when I try with GIF images (A Graphics object cannot be created from an image that has an indexed pixel format).  I know the correct way is to fork the logic to process each file type differently, but I can't work out the GIF way.

Can somebody please enlighten me?  Here is my code so far...

Dim workingImage As Image = Image.FromFile(myFileName)
Dim outputBitmap As New Bitmap(newWidth, newHeight, workingImage.PixelFormat)
Dim ImageDrawer As Graphics = Graphics.FromImage(outputBitmap) ' Exception thrown here for GIF's
ImageDrawer.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality
ImageDrawer.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic
ImageDrawer.DrawImage(workingImage, 0, 0, outputBitmap.Width, outputBitmap.Height)
Dim finalImageFormat As Imaging.ImageFormat = Imaging.ImageFormat.Jpeg
If System.IO.Path.GetExtension(myFileName).ToLower = ".gif" Then
	finalImageFormat = Imaging.ImageFormat.Gif
End If
outputBitmap.Save(HttpContext.Current.Server.MapPath(DestinationDirectory & "/" & fileNameAndExt), finalImageFormat)

  

Answer 1

User987997965 posted

Try using a MemoryStream instead.  Sorry my example is in C# but you should be able to easily convert it:

 

try

{

    byte[] imgData = getData(<PATHTOFILE>);

    System.Drawing.Image img = System.Drawing.Image.FromStream(new MemoryStream(imgData));

    Bitmap img = new Bitmap(new Bitmap( img ));

}

catch (Exception ex)

{

    

}

 

public byte[] getData(string filePath)

{

    FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);

    BinaryReader br = new BinaryReader(fs);

    byte[] data = br.ReadBytes((int)fs.Length);

    br.Close();

    fs.Close();

    return data;

}

 

Answer 2

User1090916182 posted

Hi.

Same error I'm afraid. 

I believe this problem involves working with the image, not reading it as a file.  Either way it's very frustrating.

Answer 3

User987997965 posted

Check this out:

http://www.dotnet247.com/247reference/msgs/31/159822.aspx

Answer 4

User1090916182 posted

Hi,

Yes I have seen this page already (along with lots more on my 2 days of hunting!).  The obvious question therefore is "How do you raise an image depth" ?

I can't find any full working example in ASP.NET 2 that allows a GIF or a JPG to be resized without using the infamous getThumbnail() method!  Even if I could convert a GIF to a JPG using GDI+ that might be okay (although image quality will suffer for the GIF's), but I can't find examples of that either! 

Answer 5

User987997965 posted

Hmm.  Let me try a few things and I will get back to you later on today.  If you could send me the image that is giving you the problem to: douglas.c.parsons *[at]* gmail *[dot]* com

Answer 6

User1090916182 posted

Hmm.  Let me try a few things and I will get back to you later on today.

 

Thank you.

If you could send me the image that is giving you the problem to: douglas.c.parsons *[at]* gmail *[dot]* com

 

Any GIF throws the error.  I know it is because of the indexed colour structure of GIF files in general, but I can't find a single example of how to work with it using .NET/GDI+

Answer 7

User1090916182 posted

Hang on, I'm wrong.  Not ALL gif's cause the error.

I presume this is because of the different techniques to index the colours perhaps, or maybe compression codecs... who knows?!?

Either way, here's a hyperlink to a gif that does cause the error:

http://webstyleguide.com/graphics/graphics/7.21.gif

Answer 8

User1090916182 posted

I've been continuing my search for an answer here and by dissecting code from other people's questions I have found a way to make it work.

The old code was this to create a new bitmap:

Dim outputBitmap As New Bitmap(newWidth, newHeight, workingImage.PixelFormat)

 

But if I replace it with this:

Dim outputBitmap As New Bitmap(newWidth, newHeight)

 

Then the error does not get thrown (so far).  I will investigate why this is (I presume without specifying the PixelFormat, GDI uses a generic one for the new bitmap instance?).  Either way I'd really appreciate some clarification!

Answer 9

User-1944457978 posted

Instead of: 

Dim workingImage As Image = Image.FromFile(myFileName)
Dim outputBitmap As New Bitmap(newWidth, newHeight, workingImage.PixelFormat)
Dim ImageDrawer As Graphics = Graphics.FromImage(outputBitmap) ' Exception thrown here for GIF's

Try this:

Dim workingImage as image = Image.FromFile(myFileName)
Dim TempImg As Image = New Bitmap(WorkingImage.Width, WorkingImage.Height)
Dim ImageDrawer as Graphics = Graphics.FromImage(TempImg) 

Don't worry about the original PixelFormat until you are ready to write the graphic back out to a file.

Answer 10

User1090916182 posted

 Hi bwkeller

Yes I eventually used this approach.  I wish I knew about it sooner!  The .NET framework is a lot more powerful than I imagined when it comes to image manipulation - I never thought that you would 'paint' the image and then decide on the output format.  I thought it would be the other way around.

Just out of interest, does the .NET framework use any particular picture type when working with images (i.e. for the raw canvas) ?

-- R
 

Answer 11

User1708755508 posted

 instead of

Dim outputBitmap As New Bitmap(newWidth, newHeight, workingImage.PixelFormat)

give PixelFormat.Format24bppRgb 

Answer 12

User2120868776 posted

Wait.  I don't get it.  How do you set the pixelformat outside of the bitmap's constructor method?

This is my code:

      Dim theImage As Image = Image.FromFile(sourceName.FullName)

      Dim aBitmap As System.Drawing.Bitmap = New System.Drawing.Bitmap(theImage.Width, theImage.Height)

      aBitmap.SetResolution(300, 300) ' 300 DPI

      Dim aGraphic As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(aBitmap)

      Dim MemStream As New MemoryStream()

      aGraphic.SmoothingMode = Drawing2D.SmoothingMode.HighSpeed

      aGraphic.InterpolationMode = Drawing2D.InterpolationMode.Default

      aGraphic.DrawImage(theImage, 0, 0, aBitmap.Width, aBitmap.Height)

      theImage.Dispose()

      aBitmap.PixelFormat = PixelFormat.Format1bppIndexed

      aBitmap.Save(MemStream, ImageFormat.Png)

      Dim theImage As Image = Image.FromFile(sourceName.FullName)

      Dim aBitmap As System.Drawing.Bitmap = New System.Drawing.Bitmap(theImage.Width, theImage.Height)

      aBitmap.SetResolution(300, 300) ' 300 DPI

      Dim aGraphic As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(aBitmap)

      Dim MemStream As New MemoryStream()

      aGraphic.SmoothingMode = Drawing2D.SmoothingMode.HighSpeed

      aGraphic.InterpolationMode = Drawing2D.InterpolationMode.Default

      aGraphic.DrawImage(theImage, 0, 0, aBitmap.Width, aBitmap.Height)

      theImage.Dispose()

      aBitmap.PixelFormat = PixelFormat.Format1bppIndexed ' <----- This line of code doesn't work.  I sure wish it did.

      aBitmap.Save(MemStream, ImageFormat.Png)

Answer 13

User1090916182 posted

Wait.  I don't get it.  How do you set the pixelformat outside of the bitmap's constructor method?

I'm not sure if you can.  I suppose the GDI would need to know the pixel format before it started doing anything with the image, so it would make sense to be part of the constructor method...

Answer 14

User1591353686 posted

If you use PNG format image, you can change the re-edit the image save the type to PNG24, it's fixed.