I'm trying to determine the optimal way to flip an image across the Y axis. For every pixel, there are 4 bytes, and each set of 4 bytes needs to remain together in order but get shifted. Here's the best I've come up with so far.
This only takes .1-.2s for a 1280x960 image, but with video such performance is crippling. Any suggestions?
Initial implementation
private void ReverseFrameInPlace(int width, int height, int bytesPerPixel, ref byte[] framePixels)
{
System.Diagnostics.Stopwatch s = System.Diagnostics.Stopwatch.StartNew();
int stride = width * bytesPerPixel;
int halfStride = stride / 2;
int byteJump = bytesPerPixel * 2;
int length = stride * height;
byte pix;
for (int i = 0, a = stride, b = stride - bytesPerPixel;
i < length; i++)
{
if (b % bytesPerPixel == 0)
{
b -= byteJump;
}
if (i > 0 && i % halfStride == 0)
{
i = a;
a += stride;
b = a - bytesPerPixel;
if (i >= length)
{
break;
}
}
pix = framePixels[i];
framePixels[i] = framePixels[b];
framePixels[b++] = pix;
}
s.Stop();
System.Console.WriteLine("ReverseFrameInPlace: {0}", s.Elapsed);
}
Revision #1
Revised with indexes and Buffer.BlockCopy per SLaks and Alexei. Also added a Parallel.For since the indexes allow for it.
int[] pixelIndexF = null;
int[] pixelIndexB = null;
private void ReverseFrameInPlace(int width, int height, int bytesPerPixel, byte[] framePixels)
{
System.Diagnostics.Stopwatch s = System.Diagnostics.Stopwatch.StartNew();
if (pixelIndexF == null)// || pixelIndex.Length != (width * height))
{
int stride = width * bytesPerPixel;
int length = stride * height;
pixelIndexF = new int[width * height / 2];
pixelIndexB = new int[width * height / 2];
for (int i = 0, a = stride, b = stride, index = 0;
i < length; i++)
{
b -= bytesPerPixel;
if (i > 0 && i % (width / 2 )== 0)
{
//i = a;
i += width / 2;
a += stride;
b = a - bytesPerPixel;
if (index >= pixelIndexF.Length)
{
break;
}
}
pixelIndexF[index] = i * bytesPerPixel;
pixelIndexB[index++] = b;
}
}
Parallel.For(0, pixelIndexF.Length, new Action<int>(delegate(int i)
{
byte[] buffer = new byte[bytesPerPixel];
Buffer.BlockCopy(framePixels, pixelIndexF[i], buffer, 0, bytesPerPixel);
Buffer.BlockCopy(framePixels, pixelIndexB[i], framePixels, pixelIndexF[i], bytesPerPixel);
Buffer.BlockCopy(buffer, 0, framePixels, pixelIndexB[i], bytesPerPixel);
}));
s.Stop();
System.Console.WriteLine("ReverseFrameInPlace: {0}", s.Elapsed);
}
Revision #2
private void ReverseFrameInPlace(int width, int height, System.Drawing.Imaging.PixelFormat pixelFormat, byte[] framePixels)
{
System.Diagnostics.Stopwatch s = System.Diagnostics.Stopwatch.StartNew();
System.Drawing.Rectangle imageBounds = new System.Drawing.Rectangle(0,0,width, height);
//create destination bitmap, get handle
System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height, pixelFormat);
System.Drawing.Imaging.BitmapData bitmapData = bitmap.LockBits(imageBounds, System.Drawing.Imaging.ImageLockMode.ReadWrite, bitmap.PixelFormat);
IntPtr ptr = bitmapData.Scan0;
//byte[] to bmap
System.Runtime.InteropServices.Marshal.Copy(framePixels, 0, ptr, framePixels.Length);
bitmap.UnlockBits(bitmapData);
//flip
bitmap.RotateFlip(System.Drawing.RotateFlipType.RotateNoneFlipX);
//get handle for bitmap to byte[]
bitmapData = bitmap.LockBits(imageBounds, System.Drawing.Imaging.ImageLockMode.ReadWrite, bitmap.PixelFormat);
ptr = bitmapData.Scan0;
System.Runtime.InteropServices.Marshal.Copy(ptr, framePixels, 0, framePixels.Length);
bitmap.UnlockBits(bitmapData);
s.Stop();
System.Console.WriteLine("ReverseFrameInPlace: {0}", s.Elapsed);
}
I faced almost the same issue but in my case I needed to flip the image for saving it to an .avi container.
I used the Array.Copy() method instead and suprisingly it seems faster than the others (at least, on my machine). The source image that I used was 720 x 576 pixels with 3 bytes per pixel. This method took between .001 - 0.01 seconds versus about 0.06 seconds for both your revisions.
private byte[] ReverseFrameInPlace2(int stride, byte[] framePixels)
{
System.Diagnostics.Stopwatch s = System.Diagnostics.Stopwatch.StartNew();
var reversedFramePixels = new byte[framePixels.Length];
var lines = framePixels.Length / stride;
for (var line = 0; line < lines; line++)
{
Array.Copy(framePixels, framePixels.Length - ((line + 1) * stride), reversedFramePixels, line * stride, stride);
}
s.Stop();
System.Console.WriteLine("ReverseFrameInPlace2: {0}", s.Elapsed);
return reversedFramePixels;
}
Try calling Buffer.BlockCopy on each range of 4 bytes; that should be faster.
You could parallelize execution on the CPU using any technique or use a pixel shader and do it on the GPU. If you only do that to display flipped video - you would best use DirectX and simply do a transformation on the GPU.
Couple more random things to try and measure:
pre-build array of indexes to copy to for a line (like [12,13,14,15, 8,9,10,11, 4,5,6,7, 0,1,2,3] instead of some complicated ifs executed on each line.
try copying to new destination instead of in-place.
Use one of the many transforms supplied by the .NET library:
http://msdn.microsoft.com/en-us/library/aa970271.aspx
Edit: Here's another example:
http://www.switchonthecode.com/tutorials/csharp-tutorial-image-editing-rotate
Another option might be to use the XNA framework to do manipulations on images. There is a small example of How to resize and save a Texture2D in XNA?. I have no idea how fast it is, but I could see how it should be pretty fast considering the functions are suppose to be used in games with high fps.
Related
I have a problem. I need to perform this function with lockbits. Please I need help.
public void xPix(Bitmap bmp, int n, Color cx, Color nx)
{
try
{
for (int y = 0; y < bmp.Height; y++)
{
for (int x = 0; x < bmp.Width; x += (n * 2))
{
cx = bmp.GetPixel(x, y);
if (x + n <= bmp.Width - 1) nx = bmp.GetPixel(x + n, y);
bmp.SetPixel(x, y, nx);
if (x + n <= bmp.Width - 1) bmp.SetPixel(x + n, y, cx);
}
}
}
catch { }
}
There were lots of things that didn't make sense to me about your code. I fixed the pieces that were preventing an image from appearing and here is the result. I will explain my changes after the code.
public void xPix(Bitmap bmp, int n, Color cx, Color nx)
{
var img = bmp.LockBits(new Rectangle(Point.Empty, bmp.Size), System.Drawing.Imaging.ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
byte[] bmpBytes = new byte[Math.Abs(img.Stride) * img.Height];
System.Runtime.InteropServices.Marshal.Copy(img.Scan0, bmpBytes, 0, bmpBytes.Length);
for (int y = 0; y < img.Height; y++)
{
for (int x = 0; x < img.Width; x+=n*2)
{
cx = Color.FromArgb(BitConverter.ToInt32(bmpBytes, y * Math.Abs(img.Stride) + x * 4));
if (x + n <= img.Width - 1) nx = Color.FromArgb(BitConverter.ToInt32(bmpBytes, y * Math.Abs(img.Stride) + x * 4));
BitConverter.GetBytes(nx.ToArgb()).CopyTo(bmpBytes, y * Math.Abs(img.Stride) + x * 4);
if (x + n <= img.Width - 1) BitConverter.GetBytes(cx.ToArgb()).CopyTo(bmpBytes, y * Math.Abs(img.Stride) + (x + n) * 4);
}
}
System.Runtime.InteropServices.Marshal.Copy(bmpBytes, 0, img.Scan0, bmpBytes.Length);
bmp.UnlockBits(img);
}
protected override void OnClick(EventArgs e)
{
base.OnClick(e);
Bitmap bmp = new Bitmap(#"C:\Users\bluem\Downloads\Default.png");
for (int i = 0; i < bmp.Width; i++)
{
xPix(bmp, new Random().Next(20) + 1, System.Drawing.Color.White, System.Drawing.Color.Green);
}
Canvas.Image = bmp;
}
There's no such class as LockBitmap so I replaced it with the result of a call to Bitmap.LockBits directly.
The result of LockBits does not include functions for GetPixel and SetPixel, so I did what one normally does with the result of LockBits (see https://learn.microsoft.com/en-us/dotnet/api/system.drawing.bitmap.lockbits?view=netframework-4.7.2) and copied the data into a byte array instead.
When accessing the byte data directly, some math must be done to convert the x and y coordinates into a 1-dimensional coordinate within the array of bytes, which I did.
When accessing the byte data directly under the System.Drawing.Imaging.PixelFormat.Format32bppArgb pixel format, multiple bytes must be accessed to convert between byte data and a pixel color, which I did with BitConverter.GetBytes, BitConverter.ToInt32, Color.FromArgb and Color.ToArgb.
I don't think it's a good idea to be changing the Image in the middle of painting it. You should either be drawing the image directly during the Paint event, or changing the image outside the Paint event and allowing the system to draw it. So I used the OnClick of my form to trigger the function instead.
The first random number I got was 0, so I had to add 1 to avoid an endless loop.
The cx and nx parameters never seem to be used as inputs, so I put arbitrary color values in for them. Your x and y variables were not defined/declared anywhere.
If you want faster on-image-action, you can use Marshall.Copy method with Parallel.For
Why dont use GetPixel method? Because every time you call it, your ALL image is loaded to memory. GetPixel get one pixel, and UNLOAD all image. And in every iteration, ALL image is loaded to memory (for example, if u r working on 500x500 pix image, GetPixel will load 500x500 times whole pixels to memory). When you work on images with C# (CV stuff), work on raw bytes from memory.
I will show how to use with Lockbits in Binarization because its easy to explain.
int pixelBPP = Image.GetPixelFormatSize(resultBmp.PixelFormat) / 8;
unsafe
{
BitmapData bmpData = resultBmp.LockBits(new Rectangle(0, 0, resultBmp.Width, resultBmp.Height), ImageLockMode.ReadWrite, resultBmp.PixelFormat);
byte* ptr = (byte*)bmpData.Scan0; //addres of first line
int height = resultBmp.Height;
int width = resultBmp.Width * pixelBPP;
Parallel.For(0, height, y =>
{
byte* offset = ptr + (y * bmpData.Stride); //set row
for(int x = 0; x < width; x = x + pixelBPP)
{
byte value = (offset[x] + offset[x + 1] + offset[x + 2]) / 3 > threshold ? Byte.MaxValue : Byte.MinValue;
offset[x] = value;
offset[x + 1] = value;
offset[x + 2] = value;
if (pixelBPP == 4)
{
offset[x + 3] = 255;
}
}
});
resultBmp.UnlockBits(bmpData);
}
Now, example with Marshall.copy:
BitmapData bmpData = resultBmp.LockBits(new Rectangle(0, 0, resultBmp.Width, resultBmp.Height),
ImageLockMode.ReadWrite,
resultBmp.PixelFormat
);
int bytes = bmpData.Stride * resultBmp.Height;
byte[] pixels = new byte[bytes];
Marshal.Copy(bmpData.Scan0, pixels, 0, bytes); //loading bytes to memory
int height = resultBmp.Height;
int width = resultBmp.Width;
Parallel.For(0, height - 1, y => //seting 2s and 3s
{
int offset = y * stride; //row
for (int x = 0; x < width - 1; x++)
{
int positionOfPixel = x + offset + pixelFormat; //remember about pixel format!
//do what you want with pixel
}
}
});
Marshal.Copy(pixels, 0, bmpData.Scan0, bytes); //copying bytes to bitmap
resultBmp.UnlockBits(bmpData);
Remember, when you warking with RAW bytes very important is to remember about PixelFormat. If you work on RGBA image, you need to set up every channel. (for example offset + x + pixelFormat). I showed it in Binarization example, how to deak with RGBA image with raw data. If lockbits are not fast enough, use Marshall.Copy
I am trying to combine 3 grayscale bitmaps into one color bitmap. All three grayscale images are the same size (this is based off of data from the Hubble). My logic is:
Load "blue" image and convert to PixelFormat.Format24bppRgb. Based off of that create a new byte array that is 4 times as large as the blue data array length/3 (so it will be one byte for blue, one byte for green, one byte for red, one byte for alpha per pixel since my system is little endian). Populate the "blue" bytes of the array from the "blue" bytes of the blue image (and in this first loop set the alpha byte to 255). I then load the green and red bitmaps, convert them to PixelFormat.Format24bppRgb, and pull the g/r value and add it to the correct place in the data array. The final data array then has the bgra bytes set correctly from what I can tell.
When I have the data array populated, I have used it to:
Create a PixelFormats.Bgra32 BitmapSource then convert that to a Bitmap.
Create a PixelFormat.Format32bppArgb Bitmap using the Bitmap constructor (width, height, stride, PixelForma, IntPtr)
Create a PixelFormat.Format32bppArgb Bitmap using pointers
All three ways of creating a return bitmap result in the image being "skewed" (sorry, I don't know of a better word).
The actual output (of all three ways of generating the final bitmap) is: Actual output
The desired output is something like (this was done in photoshop so it is slightly different): Desired output
The three file names (_blueFileName, _greenFileName, _redFileName) are set in the constructor and I check to make sure the files exist before creating the class. I can post that code if anyone wants it.
Can anyone tell me what I am doing wrong? I am guessing that is is due to the stride or something like that?
Note: I can't post the links to the images I am using as input as I don't have 10 reputation points. Maybe I could send the links via email or something if someone wants them as well.
Here is my code (with some stuff commented out, the comments describe what happens if each commented out block is used instead):
public Bitmap Merge()
{
// Load original "blue" bitmap.
Bitmap tblueBitmap = (Bitmap)Image.FromFile(_blueFileName);
int width = tblueBitmap.Width;
int height = tblueBitmap.Height;
// Convert to 24 bpp rgb (which is bgr on little endian machines)
Bitmap blueBitmap = new Bitmap(width, height, PixelFormat.Format24bppRgb);
using (Graphics gr = Graphics.FromImage(blueBitmap))
{
gr.DrawImage(tblueBitmap, 0, 0, width, height);
}
tblueBitmap.Dispose();
// Lock and copy to byte array.
BitmapData blueData = blueBitmap.LockBits(new Rectangle(0, 0, blueBitmap.Width, blueBitmap.Height), ImageLockMode.ReadOnly,
blueBitmap.PixelFormat);
int numbBytes = blueData.Stride*blueBitmap.Height;
byte[] blueBytes = new byte[numbBytes];
Marshal.Copy(blueData.Scan0, blueBytes, 0, numbBytes);
blueBitmap.UnlockBits(blueData);
blueData = null;
blueBitmap.Dispose();
int mult = 4;
byte[] data = new byte[(numbBytes/3)*mult];
int count = 0;
// Copy every third byte starting at 0 to the final data array (data).
for (int i = 0; i < data.Length / mult; i++)
{
// Check for overflow
if (blueBytes.Length <= count*3 + 2)
{
continue;
}
// First pass, set Alpha channel.
data[i * mult + 3] = 255;
// Set blue byte.
data[i*mult] = blueBytes[count*3];
count++;
}
// Cleanup.
blueBytes = null;
int generation = GC.GetGeneration(this);
GC.Collect(generation);
Bitmap tgreenBitmap = (Bitmap)Image.FromFile(_greenFileName);
Bitmap greenBitmap = new Bitmap(width, height, PixelFormat.Format24bppRgb);
using (Graphics gr = Graphics.FromImage(greenBitmap))
{
gr.DrawImage(tgreenBitmap, 0, 0, width, height);
}
tgreenBitmap.Dispose();
BitmapData greenData = greenBitmap.LockBits(new Rectangle(0, 0, greenBitmap.Width, greenBitmap.Height), ImageLockMode.ReadOnly,
greenBitmap.PixelFormat);
numbBytes = greenData.Stride * greenBitmap.Height;
byte[] greenBytes = new byte[numbBytes];
Marshal.Copy(greenData.Scan0, greenBytes, 0, numbBytes);
greenBitmap.UnlockBits(greenData);
greenData = null;
greenBitmap.Dispose();
count = 0;
for (int i = 0; i < data.Length / mult; i++)
{
if (greenBytes.Length <= count * 3 + 1)
{
continue;
}
// Set green byte
data[i * mult + 1] = greenBytes[count * 3 + 1];
count++;
}
greenBytes = null;
generation = GC.GetGeneration(this);
GC.Collect(generation);
Bitmap tredBitmap = (Bitmap)Image.FromFile(_redFileName);
Bitmap redBitmap = new Bitmap(width, height, PixelFormat.Format24bppRgb);
using (Graphics gr = Graphics.FromImage(redBitmap))
{
gr.DrawImage(tredBitmap, 0, 0, width, height);
}
tredBitmap.Dispose();
BitmapData redData = redBitmap.LockBits(new Rectangle(0, 0, redBitmap.Width, redBitmap.Height), ImageLockMode.ReadOnly,
redBitmap.PixelFormat);
numbBytes = redData.Stride * redBitmap.Height;
byte[] redBytes = new byte[numbBytes];
Marshal.Copy(redData.Scan0, redBytes, 0, numbBytes);
redBitmap.UnlockBits(redData);
redData = null;
redBitmap.Dispose();
count = 0;
for (int i = 0; i < data.Length / mult; i++)
{
if (redBytes.Length <= count * 3+2)
{
count++;
continue;
}
// set red byte
data[i * mult + 2] = redBytes[count * 3 + 2];
count++;
}
redBytes = null;
generation = GC.GetGeneration(this);
GC.Collect(generation);
int stride = (width*32 + 7)/8;
var bi = BitmapSource.Create(width, height, 96, 96, PixelFormats.Bgra32, null, data, stride);
// uncomment out below to see what a bitmap source to bitmap does. So far, it is exactly the same as
// the uncommented out lines below.
// ---------------------------------------------------------------------------------------------------
//return BitmapImage2Bitmap(bi);
unsafe
{
fixed (byte* p = data)
{
IntPtr ptr = (IntPtr)p;
// Trying the commented out lines returns the same bitmap as the uncommented out lines.
// ------------------------------------------------------------------------------------
byte* p2 = (byte*)ptr;
Bitmap retBitmap = new Bitmap(width, height, PixelFormat.Format32bppArgb);
BitmapData fData = retBitmap.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite,
PixelFormat.Format32bppArgb);
unsafe
{
for (int i = 0; i < fData.Height; i++)
{
byte* imgPtr = (byte*)(fData.Scan0 + (fData.Stride * i));
for (int x = 0; x < fData.Width; x++)
{
for (int ii = 0; ii < 4; ii++)
{
*imgPtr++ = *p2++;
}
//*imgPtr++ = 255;
}
}
}
retBitmap.UnlockBits(fData);
//Bitmap retBitmap = new Bitmap(width, height, GetStride(width, PixelFormat.Format32bppArgb),
// PixelFormat.Format32bppArgb, ptr);
return retBitmap;
}
}
}
private Bitmap BitmapImage2Bitmap(BitmapSource bitmapSrc)
{
using (MemoryStream outStream = new MemoryStream())
{
BitmapEncoder enc = new BmpBitmapEncoder();
enc.Frames.Add(BitmapFrame.Create(bitmapSrc));
enc.Save(outStream);
Bitmap bitmap = new Bitmap(outStream);
return new Bitmap(bitmap);
}
}
private int GetStride(int width, PixelFormat pxFormat)
{
int bitsPerPixel = ((int)pxFormat >> 8) & 0xFF;
int validBitsPerLine = width * bitsPerPixel;
int stride = ((validBitsPerLine + 31) / 32) * 4;
return stride;
}
You are missing the gap between the lines. The Stride value is not the amount of data in a line, it's the distance between the start of one line to the next. There may be a gap at the end of each line to align the next line on an even address boundary.
The Stride value can even be negative, then the image is stored upside down in memory. To get the data without the gaps and to handle all cases you need to copy one line at a time:
BitmapData blueData = blueBitmap.LockBits(new Rectangle(0, 0, blueBitmap.Width, blueBitmap.Height), ImageLockMode.ReadOnly, blueBitmap.PixelFormat);
int lineBytes = blueBitmap.Width * 3;
int numbBytes = lineBytes * blueBitmap.Height;
byte[] blueBytes = new byte[numbBytes];
for (int y = 0; y < blueBitmap.Height; y++) {
Marshal.Copy(blueData.Scan0 + y * blueData.Stride, blueBytes, y * lineBytes, lineBytes);
}
blueBitmap.UnlockBits(blueData);
blueBitmap.Dispose();
All the time the size is 1920x1080 but i want it to be for example 10x10 so the process in the function will be faster. I dont mind the size of the bitmap or its quality i just want it to be faster.
In this function im creating an histogram of each Bitmap. The problem is that the FOR loops take very long.
public static long[] GetHistogram(Bitmap b)
{
long[] myHistogram = new long[256]; // histogram סופר כמה יש מכל גוון
BitmapData bmData = null;
//b = new Bitmap(100, 100);
//b.SetPixel(0,0,Color.FromArgb(10,30,40,50)); //run and make it come to here
try
{
ResizeBitmap(b, 10, 10);
//Lock it fixed with 32bpp
bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
int scanline = bmData.Stride;
System.IntPtr Scan0 = bmData.Scan0;
unsafe
{
byte* p = (byte*)(void*)Scan0;
int nWidth = b.Width;
int nHeight = b.Height;
for (int y = 0; y < nHeight; y++)
{
for (int x = 0; x < nWidth; x++)
{
long Temp = 0;
Temp += p[0]; // p[0] - blue, p[1] - green , p[2]-red
Temp += p[1];
Temp += p[2];
Temp = (int)Temp / 3;
myHistogram[Temp]++;
//we do not need to use any offset, we always can increment by pixelsize when
//locking in 32bppArgb - mode
p += 4;
}
}
}
b.UnlockBits(bmData);
}
catch
{
try
{
b.UnlockBits(bmData);
}
catch
{
}
}
return myHistogram; // to save to a file the histogram of all the bitmaps/frames each line contain 0 to 256 values of a frame.
}
So im calling this function: ResizeBitmap(b, 10, 10);
And try to resize each bitmap but after this line i see that the bitmap size is still 1920x1080
This is the ResizeBitmap function:
public static Bitmap ResizeBitmap(Bitmap b, int nWidth, int nHeight)
{
Bitmap result = new Bitmap(nWidth, nHeight);
using (Graphics g = Graphics.FromImage((Image)result))
g.DrawImage(b, 0, 0, nWidth, nHeight);
return result;
}
Maybe there is another way to make the GetHistogram function to work faster ?
The method returns the new bitmap, so you should use the return value:
Bitmap newBitmap = ResizeBitmap(b, 10, 10);
b.Dispose();
b = newBitmap;
Side note: You are ignoring the stride of the image, which means that the pointer can go outside the image data. Consider that the stride is negative if the bitmap is stored upside down.
I've been working on a bitmap decoder, but my algorithm for processing the pixel data doesn't seem to be quite right:
public IntPtr ReadPixels(Stream fs, int offset, int width, int height, int bpp)
{
IntPtr bBits;
int pixelCount = bpp * width * height;
int Row = 0;
decimal value = ((bpp*width)/32)/4;
int RowSize = (int)Math.Ceiling(value);
int ArraySize = RowSize * Math.Abs(height);
int Col = 0;
Byte[] BMPData = new Byte[ArraySize];
BinaryReader r = new BinaryReader(fs);
r.BaseStream.Seek(offset, SeekOrigin.Begin);
while (Row < height)
{
Byte ReadByte;
if (!(Col >= RowSize))
{
ReadByte = r.ReadByte();
BMPData[(Row * RowSize) + Col] = ReadByte;
Col += 1;
}
if (Col >= RowSize)
{
Col = 0;
Row += 1;
}
}
bBits = System.Runtime.InteropServices.Marshal.AllocHGlobal(BMPData.Length);
System.Runtime.InteropServices.Marshal.Copy(BMPData, 0, bBits, BMPData.Length);
return bBits;
}
I can process only monochrome bitmaps and on some, parts of the bitmap is processed fine. None are compressed and they are rendered upside down and flipped around. I really could do with some help on this one.
decimal value = ((bpp*width)/32)/4;
int RowSize = (int)Math.Ceiling(value);
That isn't correct. Your RowSize variable is actually called "stride". You compute it like this:
int bytes = (width * bitsPerPixel + 7) / 8;
int stride = 4 * ((bytes + 3) / 4);
You are ignoring the stride.
Image rows can be padded to the left with additional Bytes to make their size divide by a number such as (1 = no padding, 2, 4, 8 = default for many images, 16, ...).
Also, images can be a rectangle region within a larger image, making the "padding" between lines in the smaller image even larger (since the stride is the larger image's stride). - In this case the image can also have an offset for its start point within the buffer.
Better practice is:
// Overload this method 3 time for different bit per SUB-pixel values (8, 16, or 32)
// = (byte, int, float)
// SUB-pixel != pixel (= 1 3 or 4 sub-pixels (grey or RGB or BGR or BGRA or RGBA or ARGB or ABGR)
unsafe
{
byte[] buffer = image.Buffer;
int stride = image.buffer.Length / image.PixelHeight;
// or int stride = image.LineSize; (or something like that)
fixed (float* regionStart = (float*)(void*)buffer) // or byte* or int* depending on datatype
{
for (int y = 0; y < height; y++) // height in pixels
{
// float* and float or byte* and byte or int* and int
float* currentPos
= regionStart + offset / SizeOf(float) + stride / SizeOf(float) * y;
for (int x = 0; x < width; x++) // width in pixels
{
for (int chan = 0; chan < channel; chan++) // 1, 3 or 4 channels
{
// DO NOT USE DECIMAL - you want accurate image values
// with best performance - primative types
// not a .NET complex type used for nice looking values for users e.g. 12.34
// instead use actual sub pixel type (float/int/byte) or double instead!
var currentValue = value;
currentPos++;
}
}
}
}
}
I find something I don't understand:
decimal value = ((bpp*width)/32)/4;
int RowSize = (int)Math.Ceiling(value);
RowSize, in my opinion, should be (bpp*width) / 8 + (bpp%8==0?0:1)
I'm currently writing a C# implementation of a little program which I have written in Java.
I had used BufferedImage.getRGB(int startX, int startY, int w, int h, int[] rgbArray, int offset, int scansize) function in my Java app. But I couldn't exactly find a version of this in C# and I am not sure how to write it manually.
There's not a direct equivalent in the .NET Framework to this method. However, if your image is a System.Drawing.Bitmap, you can call the LockBits method, and this will return a BitmapData structure that contains the address of the first scanline. You can then use it to create what should be an API-compatible wrapper. I'm assuming you're using C# 3.5 or greater, so I'm using an extension method - if you're using an older flavor, change this to a regular method by dropping the 'this' from the Bitmap argument:
public static void getRGB(this Bitmap image, int startX, int startY, int w, int h, int[] rgbArray, int offset, int scansize)
{
const int PixelWidth = 3;
const PixelFormat PixelFormat = PixelFormat.Format24bppRgb;
// En garde!
if (image == null) throw new ArgumentNullException("image");
if (rgbArray == null) throw new ArgumentNullException("rgbArray");
if (startX < 0 || startX + w > image.Width) throw new ArgumentOutOfRangeException("startX");
if (startY < 0 || startY + h > image.Height) throw new ArgumentOutOfRangeException("startY");
if (w < 0 || w > scansize || w > image.Width) throw new ArgumentOutOfRangeException("w");
if (h < 0 || (rgbArray.Length < offset + h * scansize) || h > image.Height) throw new ArgumentOutOfRangeException("h");
BitmapData data = image.LockBits(new Rectangle(startX, startY, w, h), System.Drawing.Imaging.ImageLockMode.ReadOnly, PixelFormat);
try
{
byte[] pixelData = new Byte[data.Stride];
for (int scanline = 0; scanline < data.Height; scanline++)
{
Marshal.Copy(data.Scan0 + (scanline * data.Stride), pixelData, 0, data.Stride);
for (int pixeloffset = 0; pixeloffset < data.Width; pixeloffset++)
{
// PixelFormat.Format32bppRgb means the data is stored
// in memory as BGR. We want RGB, so we must do some
// bit-shuffling.
rgbArray[offset + (scanline * scansize) + pixeloffset] =
(pixelData[pixeloffset * PixelWidth + 2] << 16) + // R
(pixelData[pixeloffset * PixelWidth + 1] << 8) + // G
pixelData[pixeloffset * PixelWidth]; // B
}
}
}
finally
{
image.UnlockBits(data);
}
}
This wrapper can now be called like this:
Bitmap foo = Bitmap.FromFile(#"somefile.jpg") as Bitmap;
int[] rgbArray = new int[100];
foo.getRGB(1, 1, 10, 10, rgbArray, 0, 10);
Hope this helps, and welcome to .NET!
You'd use Bitmap.LockBits to get direct access to the pixels in a bitmap. Here's a sample implementation, it returns one scanline from the passed bitmap as an int[]:
int[] getRGB(Bitmap bmp, int line) {
var data = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),
System.Drawing.Imaging.ImageLockMode.ReadOnly,
System.Drawing.Imaging.PixelFormat.Format32bppRgb);
try {
var ptr = (IntPtr)((long)data.Scan0 + data.Stride * (bmp.Height - line - 1));
var ret = new int[bmp.Width];
System.Runtime.InteropServices.Marshal.Copy(ptr, ret, 0, ret.Length * 4);
return ret;
}
finally {
bmp.UnlockBits(data);
}
}
I think the closest one is Bitmap.GetPixel(x,y) that return a single pixel color at a point.
In order to simulate the java function, you will need to write some helper.
You may need to check
Bitmap.GetPixel
Bitmap.LockBits
Also check Converting an array of Pixels to an image in C#.
It depends how fast you need to do it.
Bitmap has GetPixel() method which works fine for a pixel.
If you need to do fast image processing you need to use LockBits which you can find a sample here.
Bitmap img = (Bitmap) Image.FromFile(imageFileName);
BitmapData data = img.LockBits(new Rectangle(0,0,img.Width, img.Height), ImageLockMode.ReadWrite, img.PixelFormat);
byte* ptr = (byte*) data.Scan0;
for (int j = 0; j < data.Height; j++)
{
byte* scanPtr = ptr + (j * data.Stride);
for (int i = 0; i < data.width; i++, scanPtr+=NO_OF_CHANNELS)
{
for (int m = 0; m < NO_OF_CHANNELS; m++)
Console.WriteLine(*scanPtr); // value of each channel
}
}
img.UnlockBits(data);