Check if Clipboard.GetImage() is transparent in C# - c#

I think I have a simple problem that seems very hard for me to figure out - how to check if an image I get from Clipboard.GetImage() uses transparency. If it does then I will show it in a PictureBox with the transparent background.
I copy the picture directly from the application - e.g. the browser or one of the Windows image viewers. Pasting the picture to e.g. Word will get the transparent background.
I am using this code:
// Check if the picture in clipboard has any transparency (alpha channel != 255)
Bitmap img = new Bitmap(Clipboard.GetImage());
for (int y = 0; y < img.Height; ++y)
{
for (int x = 0; x < img.Width; ++x)
{
if (img.GetPixel(x, y).A != 255)
{
Debug.WriteLine("Picture is transparent - set breakpoint here");
}
}
}
...
// Show the picture with transparent background - this works fine
img.MakeTransparent(img.GetPixel(0,0));
myPictureBox.Image = (Image)img;
I am trying with various pictures found on the net and I can copy/paste those pictures with the transparent background so I know they are transparent but no pictures will trigger the Debug.WriteLine and all values equals 255?
Though I recognize this has been asked before then I must be doing something wrong since this simple example does not work? Also they are old so maybe there is a new and better way? I have tried to find other solutions besides these:
Detecting if a PNG image file is a Transparent image?
Check to see if image is transparent
.. and more also not from StackOverflow. I have seen both really simple solutions and horrofying complex ones - but still none of them seems to work.
is this because the clipboard object cannot see the transparency or .. ?

I ended up this solution, based on the comment from #Jeff, CopyTransparentImages. This will get the (real?) image from the clipboard (which will also include the alpha channel) and then I will check if the image contains any transparency afterwards. If it does then I will make the image background color transparent, according to my original question, before I show it in a PictureBox.
// Get the image formats from clipboard and check if it is transparent
Image imgCopy = GetImageFromClipboard();
bool isClipboardImageTransparent = IsImageTransparent(imgCopy);
if (isClipboardImageTransparent)
{
...
}
// Get the real image from clipboard (this supports the alpha channel)
private Image GetImageFromClipboard()
{
if (Clipboard.GetDataObject() == null) return null;
if (Clipboard.GetDataObject().GetDataPresent(DataFormats.Dib))
{
// Sometimes getting the image data fails and results in a "System.NullReferenceException" error - probably because clipboard handling also can be messy and complex
byte[] dib;
try
{
dib = ((System.IO.MemoryStream)Clipboard.GetData(DataFormats.Dib)).ToArray();
}
catch (Exception ex)
{
return Clipboard.ContainsImage() ? Clipboard.GetImage() : null;
}
var width = BitConverter.ToInt32(dib, 4);
var height = BitConverter.ToInt32(dib, 8);
var bpp = BitConverter.ToInt16(dib, 14);
if (bpp == 32)
{
var gch = GCHandle.Alloc(dib, GCHandleType.Pinned);
Bitmap bmp = null;
try
{
var ptr = new IntPtr((long)gch.AddrOfPinnedObject() + 40);
bmp = new Bitmap(width, height, width * 4, System.Drawing.Imaging.PixelFormat.Format32bppArgb, ptr);
return new Bitmap(bmp);
}
finally
{
gch.Free();
if (bmp != null) bmp.Dispose();
}
}
}
return Clipboard.ContainsImage() ? Clipboard.GetImage() : null;
}
// Check if the image contains any transparency
private static bool IsImageTransparent(Image image)
{
Bitmap img = new Bitmap(image);
for (int y = 0; y < img.Height; ++y)
{
for (int x = 0; x < img.Width; ++x)
{
if (img.GetPixel(x, y).A != 255)
{
return true;
}
}
}
return false;
}
At least this is working for me :-)

Related

Adding transparency to a SKBitmap image results in black background

I'm currently facing a problem showing a transparent image in a Xamarin.Forms Image view.
The image is retrieved from the gallery, and converted to PNG format.
Pixels are iterated and with some of them, their alpha value is adjusted.
Bitmap is converted to SKBitmapImageSource and shown in an Image view.
Result (top), and original (bottom), taken on Android:
Screenshot
The goal is to show the Image with a transparent background, but I can't get it to work. It keeps showing with a black background. Loading a transparent PNG file from internet works, so something in the process of conversion or image processing must go wrong.
Image retrieval and conversion:
SKBitmap source = SKBitmap.Decode(file.GetStream());
SKData data = SKImage.FromBitmap(source).Encode(SKEncodedImageFormat.Png, 100);
SKBitmap converted = SKBitmap.Decode(data);
SKBitmap result = ImageProcessor.AddTransparency(converted, 0.7f);
Transparency added:
public static SKBitmap AddTransparency(SKBitmap bitmapSource, float treshold)
{
if (bitmapSource == null)
{
throw new ArgumentNullException(nameof(bitmapSource), $"{nameof(bitmapSource)} is null.");
}
var bitmapTarget = bitmapSource.Copy();
// Calculate the treshold as a number between 0 and 255
int value = (int)(255 * treshold);
// loop trough every pixel
int width = bitmapTarget.Width;
int height = bitmapTarget.Height;
for (int row = 0; row < height; row++)
{
for (int col = 0; col < width; col++)
{
var color = bitmapTarget.GetPixel(col, row);
if (color.Red > value && color.Green > value && color.Blue > value)
{
bitmapTarget.SetPixel(col, row, color.WithAlpha(0x00));
}
}
}
return bitmapTarget;
}
Conversion to imagesource:
return SKBitmapImageSource.FromStream(SKImage.FromBitmap((SKBitmap)value).Encode().AsStream);
The problem is the AlphaType being set incorrectly. For the way you're doing the alpha conversion, the AlphaType should be set to AlphaType.Premul
Since it's a readonly property, copy the bitmap to a new one and set the correct alpha type

How to draw what is inside a contour in an image but leave everything else blank?

I have a colour image of type Image<Hsv, Byte>, and another image of type Image<Gray, Byte> of the same size that is all black with some all-white shapes. From the black and white image, I found the contours of the shapes using findContours(). What I want is to create a new image or modify the original colour image I have to show only what corresponds to inside the contours, with everything else being transparent, without having to check pixel by pixel values of the two images (did this, it takes too long). Any possible way to do this?
For example, I have the original image, the black and white image, and the final product I need.
I'm completely new to emgucv, so, I'm not saying this is the best approach; but it seems to work.
Create a new draw surface
Draw the original image
Change the white pixels in the mask image to transparent pixels
Draw the transparent mask on top of the original image
The result image looks like your desired outcome.
void Main()
{
var path = Path.Combine(
Environment.GetFolderPath(Environment.SpecialFolder.Desktop),
"images");
var original = new Image<Bgr, Byte>(Path.Combine(path, "vz7Oo1W.png"));
var mask = new Image<Bgr, Byte>(Path.Combine(path, "vIQUvUU.png"));
var bitmap = new Bitmap(original.Width, original.Height);
using (Graphics g = Graphics.FromImage(bitmap))
{
g.DrawImage(original.Bitmap, 0, 0);
g.DrawImage(MakeTransparent(mask.Bitmap), 0, 0);
}
bitmap.Save(Path.Combine(path, "new.png"));
}
public static Bitmap MakeTransparent(Bitmap image)
{
Bitmap b = new Bitmap(image);
var tolerance = 10;
for (int i = b.Size.Width - 1; i >= 0; i--)
{
for (int j = b.Size.Height - 1; j >= 0; j--)
{
var col = b.GetPixel(i, j);
col.Dump();
if (255 - col.R < tolerance &&
255 - col.G < tolerance &&
255 - col.B < tolerance)
{
b.SetPixel(i, j, Color.Transparent);
}
}
}
return b;
}

How to detect where the image content ends?

I receive images of the same size but with different amounts of information. Examples below (red borders are mine). The background is always white.
I am trying to detect where the information on the image ends - at what pixel height (and crop accordingly). In other words, find the first non-white pixel from the bottom.
Is there a better way to do this other than extract BitmapData out of Image object and loop through all the pixels?
Just to add a suggestion having looked over your images and your solution (below) and your method is fine but you may be able to improve efficiency.
The more you know about your image the better; you're confident the background is always white (according to your post, the code is a more generic utility but the following suggestion can still work); can you be confident on the furthest point in a non-white pixel will be found if the row is not empty?
For example; in your two pictures the furthest in non-white pixel on a row is about 60px in. If this is universally true for your data then you don't need to scan the whole line of the image, which would make your for loop:
for (int y = bitmap.Height - 1; y >= 0; y--) {
for (int x = 0; x < 60; x++) {
Color color = bitmap.GetPixel(x, y);
if (color.R != backColor.R || color.G != backColor.G || color.B != backColor.B) {
foundContentOnRow = y;
break;
}
}
}
(You could make it a parameter on the function so you can easily control it if needed).
Imagine for example that the first non-white row was 80px down. To find it currently you do 640 x 300 = 192,000 checks. If you could confidently say that you would know a row was blank within 100 pixels (an over-estimate based on the data presented) then this would be 100 * 300 = 30,000 checks per image.
If you always knew that the first 10 pixels of the image were always blank you could shave a little bit more off (say 3000 checks).
Musing on a setup where you knew that the first non-white pixel was between 10 and 60 pixels in (range of 50) you could find it at row 80 in 50 x 300 = 15,000 checks which is a good reduction.
Of course the downside about assumptions is that if things change your assumptions may not be valid, but if the data is going to remain fairly constant then it may be worthwhile, especially if you do this for a lot of images.
I've ended up using the following code to trim the image. Hopefully someone finds this useful.
class Program {
static void Main(string[] args) {
Image full = Image.FromFile("foo.png");
Image cropped = full.TrimOnBottom();
}
}
public static class ImageUtilities {
public static Image TrimOnBottom(this Image image, Color? backgroundColor = null, int margin = 30) {
var bitmap = (Bitmap)image;
int foundContentOnRow = -1;
// handle empty optional parameter
var backColor = backgroundColor ?? Color.White;
// scan the image from the bottom up, left to right
for (int y = bitmap.Height - 1; y >= 0; y--) {
for (int x = 0; x < bitmap.Width; x++) {
Color color = bitmap.GetPixel(x, y);
if (color.R != backColor.R || color.G != backColor.G || color.B != backColor.B) {
foundContentOnRow = y;
break;
}
}
// exit loop if content found
if (foundContentOnRow > -1) {
break;
}
}
if (foundContentOnRow > -1) {
int proposedHeight = foundContentOnRow + margin;
// only trim if proposed height smaller than existing image
if (proposedHeight < bitmap.Height) {
return CropImage(image, bitmap.Width, proposedHeight);
}
}
return image;
}
private static Image CropImage(Image image, int width, int height) {
Rectangle cropArea = new Rectangle(0, 0, width, height);
Bitmap bitmap = new Bitmap(image);
return bitmap.Clone(cropArea, bitmap.PixelFormat);
}
}

C# WinForms Out of Memory Exception on Bitmap Clone

I've written a small "watermark" program to add a custom watermark to an image. There are two watermarks a white one and a black one. The watermark is always placed on the left bottom side of the image. I clone that region of the image to determine which watermark should be placed based on that spot (the black watermark on light regions and the white watermark on dark regions).
When I use the application (either in debug or normal) on my machine - no problem. All images are processed and watermarks are added on the correct location.
However, on the client machine, the program breaks on all images throwing a OutOfMemory Exception on the clone part.
I know, ussually, the OutOfMemory Exception will also be thrown when I specify a region out of bounds, but since the function is working like a charm on my machine I can't imagine that is the case. Besides that, the program doesn't break after a few tries, it breaks on all attempts to clone.
Doesn't matter if there is text (DrawString method) or not. It breaks on the Clone.
The images being processed are big, but not "huge" (6016 x 4000 pixels at most) but even with smaller images (3264 x 2448 pixels) the client will break.
Variables:
bmOriginal : original bitmap
processImage : original image (pictureBox) - bmOriginal is a bitmap copy of this
watermarkText : textbox for extra information below watermark
black and white : pictureboxes containing the watermark images
watermarkCombo : combobox for selecting automatic, white or black (automatic fails)
Code:
using (Graphics gWatermark = Graphics.FromImage(bmOriginal))
{
gWatermark.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
System.Drawing.SolidBrush drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.Black);
// position watermark - watermark should be 10% of the image height
int watermarkHeight = (int)(processImage.Image.Height * 0.1);
int watermarkPadding = (int)(watermarkHeight * 0.1); // not completely true, but asume watermark is square
Rectangle watermarkArea = new Rectangle(watermarkPadding, processImage.Image.Height - (watermarkPadding + (watermarkText.Text.Length == 0 ? 0 : watermarkPadding) + watermarkHeight), watermarkHeight, watermarkHeight);
// determine color watermark
bmWatermark = (Bitmap)black.Image;
if (watermarkCombo.SelectedIndex == 0)
{
using (Bitmap watermarkClone = bmOriginal.Clone(watermarkArea, bmOriginal.PixelFormat))
{
var pixels = Pixels(watermarkClone);
if (pixels.Average((Func<Color, decimal>)Intensity) < 110) // human eye adoption; normal threshold should be 128
{
bmWatermark = (Bitmap)white.Image;
drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.White);
}
}
}
else if (watermarkCombo.SelectedIndex == 1)
{
bmWatermark = (Bitmap)white.Image;
drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.White);
}
// draw the watermark
gWatermark.DrawImage(bmWatermark, watermarkArea.X, watermarkArea.Y, watermarkArea.Width, watermarkArea.Height);
// draw the text (if needed)
if (watermarkText.Text.Length > 0)
{
System.Drawing.Font drawFont = new System.Drawing.Font("Tahoma", (float)watermarkPadding);
gWatermark.DrawString(watermarkText.Text, drawFont, drawBrush, watermarkPadding, bmOriginal.Height - (watermarkPadding * 2));
}
}
bmOriginal.Save(System.IO.Path.Combine(diWatermarked.FullName, fileName), System.Drawing.Imaging.ImageFormat.Jpeg);
line of error: using (Bitmap watermarkClone = bmOriginal.Clone(watermarkArea, bmOriginal.PixelFormat))
Now the big question: how do I get rid of that OutOfMemory exception.. anyone an idea?
EDIT When I choose not to determine the color of the watermark automatically and just add a watermark (let's say the white one) the program functions normally. I've seen the stack trace in an error log (on the catch of the function I output the exception and -if any- inner exceptions).
I know a lot of the OOM exceptions using the Clone function occur when you specify a region out of bounds; but that is not the case here.
When I look at my memory when using the app in debug mode, I start at 5.36 Gb program started and a normalized 5.39 Gb (with a max spike of 5.42 Gb) when running the execution I mentioned, it's not guzzling memory like crazy.
The code I use the determine the average "color" (it's from someone on StackOverflow - I just copied that from some other answer, can't find the link though);
// functions used to determine watermark color
private static decimal ComponentAverage(decimal a, decimal b)
{
return Math.Min(a, b) + Math.Abs(a - b) / 2M;
}
private static decimal Intensity(Color color)
{
decimal result = color.A;
result = ComponentAverage(result, color.R);
result = ComponentAverage(result, color.G);
result = ComponentAverage(result, color.B);
return result;
}
private static IEnumerable<Color> Pixels(Bitmap bitmap)
{
for (int x = 0; x < bitmap.Width; x++)
for (int y = 0; y < bitmap.Height; y++)
yield return bitmap.GetPixel(x, y);
}
SOURCE There is a test project here: http://hotpepper.nu/oomtestapp.zip
Leon, I've changed your code you've uploaded to not lock any resources.
I've notices that if I keep your application open, I cannot delete the output folders because some files are in use. This usually means that you DID NOT release all file handles, basically it is always the last file.
I couldn't reproduce the out of memory issue on my computer before and after my changes, seems to be an issue with very big files maybe?
Ok anyways, I found that you use ImageBox to load the white and black resource and to load the image from disc. This is not needed at all, intead use the resources directly
Bitmap white = OomTestApp.Properties.Resources.white;
Bitmap black = OomTestApp.Properties.Resources.black;
Then to load an image from disc, simply use Bitmap.FromFile
I have added some lines to release your resources properly .Dispose where no using blocks are used.
And I also removed the Clone() call because it is absolutely not needed I think, because you are just computing the pixels of the original image and you do not draw something into that image at that point. So what was the need to have the image cloned?
Here is the full code (starting after you created the folders)
if (errors == 0)
{
this.Height = 323;
goButton.Enabled = false;
stopButton.Enabled = true;
Bitmap white = OomTestApp.Properties.Resources.white;
Bitmap black = OomTestApp.Properties.Resources.black;
Bitmap bmWatermark = black;
Bitmap processImage = null;
progressBar1.Maximum = filesToProcess.Count;
foreach (string handleFile in filesToProcess)
{
string fileName = System.IO.Path.GetFileName(handleFile);
fileNameLabel.Text = "File: " + System.IO.Path.GetFileName(handleFile);
try
{
// create backup if checked
if (diOriginal != null)
{
System.IO.File.Move(handleFile, System.IO.Path.Combine(diOriginal.FullName, fileName));
processImage = (Bitmap)Bitmap.FromFile(System.IO.Path.Combine(diOriginal.FullName, fileName));
}
else
{
processImage = (Bitmap)Bitmap.FromFile(handleFile);
}
double aspectRatio = (double)processImage.Width / (double)processImage.Height;
using (Graphics gWatermark = Graphics.FromImage(processImage))
{
gWatermark.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
System.Drawing.SolidBrush drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.Black);
// position watermark - watermark should be 10% of the image height
int watermarkHeight = (int)(processImage.Height * 0.1);
int watermarkPadding = (int)(watermarkHeight * 0.1); // not completely true, but asume watermark is square
// calculate rectangle. if there is extra text, add extra padding below
Rectangle watermarkArea = new Rectangle(watermarkPadding, processImage.Height - (watermarkPadding + (watermarkText.Text.Length == 0 ? 0 : watermarkPadding) + watermarkHeight), watermarkHeight, watermarkHeight);
// determine color watermark
bmWatermark = black;
if (watermarkCombo.SelectedIndex == 0)
{
/*using (Bitmap watermarkClone = processImage.Clone(watermarkArea, processImage.PixelFormat))
{*/
var pixels = Pixels(processImage);
if (pixels.Average((Func<Color, decimal>)Intensity) < 110) // human eye adoption; normal threshold should be 128
{
bmWatermark = white;
drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.White);
}
//}
}
else if (watermarkCombo.SelectedIndex == 1)
{
bmWatermark = white;
drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.White);
}
// draw the watermark
gWatermark.DrawImage(bmWatermark, watermarkArea.X, watermarkArea.Y, watermarkArea.Width, watermarkArea.Height);
// draw the text (if needed)
if (watermarkText.Text.Length > 0)
{
System.Drawing.Font drawFont = new System.Drawing.Font("Tahoma", (float)watermarkPadding);
gWatermark.DrawString(watermarkText.Text, drawFont, drawBrush, watermarkPadding, processImage.Height - (watermarkPadding * 2));
drawFont.Dispose();
}
// disposing resources
drawBrush.Dispose();
}
// save the watermarked file
processImage.Save(System.IO.Path.Combine(diWatermarked.FullName, fileName), System.Drawing.Imaging.ImageFormat.Jpeg);
// stop button pressed?
Application.DoEvents();
if (stopProcess) break;
// update exection progress
progressBar1.Value++;
percentLabel.Text = ((int)((progressBar1.Value * 100) / filesToProcess.Count)).ToString() + "%";
fileCountLabel.Text = "File " + progressBar1.Value.ToString() + "/" + filesToProcess.Count.ToString();
}
catch (Exception ex)
{
try
{
using (System.IO.StreamWriter sw = new System.IO.StreamWriter(System.IO.Path.Combine(folderText.Text, "errorlog.txt"), true))
{
sw.WriteLine("File: " + fileName);
while (ex != null)
{
sw.WriteLine("Message: " + ex.Message);
sw.WriteLine(ex.StackTrace);
sw.WriteLine(ex.Source);
ex = ex.InnerException;
}
sw.WriteLine();
}
}
catch
{
// nothing to do - it already failed
}
errors++;
}
finally
{
if (processImage != null) processImage.Dispose();
}
}
// dispose resources
white.Dispose();
black.Dispose();
bmWatermark.Dispose();
if (!stopProcess)
{
// set status to complete
fileCountLabel.Text = "File " + filesToProcess.Count.ToString() + "/" + filesToProcess.Count.ToString();
percentLabel.Text = "100%";
fileNameLabel.Text = "Completed...";
}
else
{
fileNameLabel.Text = "Aborted...";
}
fileNameLabel.Text += errors.ToString() + " error(s) encountered";
// defaults to screen
progressBar1.Value = progressBar1.Maximum;
stopProcess = false;
goButton.Enabled = true;
stopButton.Enabled = false;
Well, I didn't read everything on the page, but I wonder if anyone mentioned the "stride" of the Bitmap? Basically, your bitmap has to be a multiple of 4 bytes.
I had this problem taking apart a grid to make tiles. The last tile would error because the Bitmap was not evenly divisible by 4.
The stride is the width of a single row of pixels (a scan line),
rounded up to a four-byte boundary. If the stride is positive, the
bitmap is top-down. If the stride is negative, the bitmap is
bottom-up.
https://softwarebydefault.com/2013/04/11/bitmap-color-balance/

C# - Crop Transparent/White space

I'm trying to remove all white or transparent pixels from an image, leaving the actual image (cropped). I've tried a few solutions, but none seem to work. Any suggestions or am I going to spend the night writing image cropping code?
So, what you want to do is find the top, left most non white/transparent pixel and the bottom, right most non white/transparent pixel. These two coordinates will give you a rectangle that you can then extract.
// Load the bitmap
Bitmap originalBitmap = Bitmap.FromFile("d:\\temp\\test.bmp") as Bitmap;
// Find the min/max non-white/transparent pixels
Point min = new Point(int.MaxValue, int.MaxValue);
Point max = new Point(int.MinValue, int.MinValue);
for (int x = 0; x < originalBitmap.Width; ++x)
{
for (int y = 0; y < originalBitmap.Height; ++y)
{
Color pixelColor = originalBitmap.GetPixel(x, y);
if (!(pixelColor.R == 255 && pixelColor.G == 255 && pixelColor.B == 255)
|| pixelColor.A < 255)
{
if (x < min.X) min.X = x;
if (y < min.Y) min.Y = y;
if (x > max.X) max.X = x;
if (y > max.Y) max.Y = y;
}
}
}
// Create a new bitmap from the crop rectangle
Rectangle cropRectangle = new Rectangle(min.X, min.Y, max.X - min.X, max.Y - min.Y);
Bitmap newBitmap = new Bitmap(cropRectangle.Width, cropRectangle.Height);
using (Graphics g = Graphics.FromImage(newBitmap))
{
g.DrawImage(originalBitmap, 0, 0, cropRectangle, GraphicsUnit.Pixel);
}
public Bitmap CropBitmap(Bitmap original)
{
// determine new left
int newLeft = -1;
for (int x = 0; x < original.Width; x++)
{
for (int y = 0; y < original.Height; y++)
{
Color color = original.GetPixel(x, y);
if ((color.R != 255) || (color.G != 255) || (color.B != 255) ||
(color.A != 0))
{
// this pixel is either not white or not fully transparent
newLeft = x;
break;
}
}
if (newLeft != -1)
{
break;
}
// repeat logic for new right, top and bottom
}
Bitmap ret = new Bitmap(newRight - newLeft, newTop - newBottom);
using (Graphics g = Graphics.FromImage(ret)
{
// copy from the original onto the new, using the new coordinates as
// source coordinates for the original
g.DrawImage(...);
}
return ret
}
Note that this function will be slow as dirt. GetPixel() is unbelievably slow, and accessing the Width and Height properties of a Bitmap inside a loop is also slow. LockBits would be the proper way to do this - there are tons of examples here on StackOverflow.
Per-pixel check should do the trick. Scan each line to find empty line from the top & bottom, scan each row to find left & right constraints (this can be done in one pass with either rows or columns). When the constraint is found - copy the part of the image to another buffer.
In WPF we have a WriteableBitmap class. Is this what are you looking for ? If it is the case please have a look at http://blogs.msdn.com/b/jgalasyn/archive/2008/04/17/using-writeablebitmap-to-display-a-procedural-texture.aspx
I found a method to batch trim a few thousand .jpg files in about 10 minutes, but I didn't do it in code. I used the Convert feature of Snag-It Editor. I don't know if this is an option for you, if you need to do this trimming once or your need is ongoing, but for the price of the software, which isn't a whole lot, I considered this a decent workaround.
(I do not work for or represent Techsmith.)
Joey
Adding to this, if you are in WPF and you have excess space around your image, check the properties of the image and make sure your Stretch property is set to fill. This eliminated the space around the image.
Screen shot of the property in WPF

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