FastPix: Rapid Pixel Processing for Dummies and Dudes

[boops boops]

People are forever complaining about the slowness of GetPixel and SetPixel. They probably weren't designed for processing whole images (or if they were, they were designed very badly). DotNet has an answer to that, but it's not an easy one to get your head around: the Bitmap class methods LockBits and UnlockBits.

The main idea of FastPix is to provide a substitute for GetPixel and SetPixel which seem to work about 10 to 15 times as fast as the original ones. But it has more to offer.

There are plenty of examples on the web of classes that encapsulate LockBits/UnlockBits. The ones I have seen are often complicated because they try to deal with many different bitmap formats. But as far as I can see nearly all the bitmaps we deal with are either 24 bits (digital photos, some drawing programs) or 32 bits (drawing programs with transparency). GDI+ converts 24 bit images internally to 32 bits anyway, so I have designed FastPix to work with 32 bits only. It makes the code simpler and opens up the possibility of processing bitmaps as Integer arrays, which are blindingly fast. FastPix includes a ConvertFormat method for converting bitmap pixel formats.

To start using Fastpix, download the attached zip file and unzip it to a convenient folder. In Visual Studio, select Project/Add Existing Item... and import the unzipped .vb file into your project.

Here is an example of how you use the FastPix GetPixel and SetPixel substitutes. Their format is the same as the ones in the Bitmap class:

Using fp as New FastPix(myBitmap)
       Dim myColor As Color =  fp.GetPixel(x, y)
       fp.SetPixel(x, y, Color.Orange)
    End Using

Always declare a FastPix object with a Using loop, or otherwise Dispose it as soon as you have finished with it. The UnLockBits is in the Dispose method, so you will not be able to see your resulting bitmap until Dispose has been called either implicitly (with End Using) or directly.

FastPix also offers you the bitmap in the form of an Integer Array and its performance leaves even the Fastpix GetBitmap/SetBitmap in the dust. Here's an example of how you use it:

Using fp as New FastPix(myBitmap)
           'Make a local reference to the array; it is roughly 4x as fast as direct references to fp.PixelArray:
           Dim pixels as Integer() = fp.PixelArray
 
              For i as integer = 0 to pixels.Length - 1
 
                   'example: substitute a color
                   if pixels(i) = Color.Red.ToArgb then pixels(i) = Color.Blue.ToArgb
 
                   'example: invert the color
                   pixels(i) = pixels(i) XOR $HFFFFFF
 
               Next
            End Using

Note how the inversion is done using only a logical instruction and a bit mask. If you can restrict yourself to techiques like that and to integer arithmetic, and avoid all references to objects outside the Class, you can get fantastic performance. For example, inverting the colors of a 10 MP digital photo can be done over 100x as fast as with old-fashioned GetPixel and SetPixel (150x if you don't count the LockBits/UnlockBits overhead).

Of course, many kinds of pixel processing require you to get at the A, R, G and B bytes of the pixel. You can extract those from an integer using the BitConverter.GetBytes method, but that would slow things down terribly. Instead, it is possible to extract the bytes with masks and logic/shift operations only. They are probably just as fast as integer arithmetic. Here is an example which fades a bitmap by levelling all the Alpha byte values to a maximum level:

Dim _alpha As Byte 'Level Alpha down to this value
 
Using fp as New FastPix(myBitmap)
   Dim pixels as Integer() = fp.PixelArray
   Dim px As Integer = pixels(j)
   Dim pxAlpha As Integer = (px >> 24) And &HFF 'shift alpha byte to bottom end, clear rest
   If pxAlpha > _alpha Then 
      pxAlpha = CInt(_alpha) << 24
      pixels(j) = (px And &HFFFFFF) Or pxAlpha 'replace original alpha value
   End If 
End Using

If you don't like the look of that, FastPix also provides a Byte array to make byte operations a bit less intimidating. Possibly it's not as fast as the integer array version. The bytes are in the order A, R, G, B for each pixel. Here's another example of fading a bitmap. Note the extra parameter in the FastPix declaration:

Using fp As New FastPix(myBitmap, True)
   Dim bytes As byte() = fp.ColorByteArray
   'Modify the Alpha bytes to make the bitmap 50% transparent:
    For i As Integer = 0 to bytes.Length - 1 Step 4    
       bytes(i) = 127
    Next
End Using

I hope you find it useful. Comments and criticism welcome. BB

[tan2010]

Wow, your code looks very lean and effective. How do i apply it to my project so that it can help me sharpen the image using track bar.
Please show me some coding!

[boops boops]

Thanks for the compliment. I may be able to help you improve the performance, but I won't have time today. I'll look at it in the weekend. BB

[formlesstree4]

This is a great entry into the codebank boops, well done!

[Schravendeel]

Wow. Cant believe that this has so few replies. This is just pure epicness! As you said, the slowness of GetPixel and SetPixel has always annoyed me, this finally fixes this issue. Yay!

Many for you sir!

[moti barski]

Using fp as New FastPix(myBitmap)

myBitmap = bitmap variable ?

[boops boops]

@Schravendeel. Thanks for your compliments!
@Moti. Yes, it just stand for the name of your own bitmap. Sorry it wasn't clear.
@Everyone. New version coming soon!

BB

[moti barski]

testing report :
form controls :
picturebox : with image in it, streched
button
textbox

code used with fast pix class :

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim bm As Bitmap
        bm = PictureBox1.Image
        Using fp As New FastPix(bm)
            Dim myColor As Color = fp.GetPixel(20, 20)
            fp.SetPixel(20, 20, Color.Orange)
            TextBox1.Text = myColor.ToString
        End Using
    End Sub
End Class

a glitch fired up :

A first chance exception of type 'System.FormatException' occurred in pixelTest1.exe

in the class line (after the if line):

If pFSize <> 32 OrElse bmp.PixelFormat = PixelFormat.Indexed Then
Throw New FormatException _
("FastPix is designed to deal only with 32-bit pixel non-indexed formats. Your bitmap has " _
& pFSize & "-bit pixels. You can convert it using FastPix.ConvertFormat.")
Else

[formlesstree4]

Moti, it specifically tells you how to deal with the problem right in the error message.

[moti barski]

only .bmp ?

[formlesstree4]

The program tells you the exact call to use in order to (hopefully) remove the error.

[moti barski]

please stop the guessing game

this also glitches:

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim bm As Bitmap
        bm = PictureBox1.Image
        Using fp As New FastPix(bm)
            FastPix.ConvertFormat(bm, Imaging.PixelFormat.Alpha)
            Dim myColor As Color = fp.GetPixel(20, 20)
            fp.SetPixel(20, 20, Color.Orange)
            TextBox1.Text = myColor.ToString
        End Using

    End Sub
End Class

[formlesstree4]

You don't seem to get it. I'm not guessing; I'm telling you exactly what you need to hear. You need to convert it before you actually use the image otherwise you'll throw the exception. You know the method to use to perform the conversion, just change where it's being called. It's not that hard.

[moti barski]

this ? FastPix.ConvertFormat(bm, Imaging.PixelFormat.Alpha)
where should it go ?

[formlesstree4]

Before the Using statement...

[moti barski]

Before the Using statement...

A first chance exception of type 'System.ArgumentException' occurred in System.Drawing.dll

at the situation

[formlesstree4]

How is that my problem? That's an exception in System.Drawing.dll, not FastPixel. Try wrapping Try-Catch statements around it and see what you get. Don't get mad at the person that's hand-feeding you help and try using some common logic to fix a problem.

[moti barski]

I am not mad at you you're cool the glitches are what got to me
I"ll just hope senior boobs hook me up with a walkthrough

[Nightwalker83]

I am not mad at you you're cool the glitches are what got to me
I"ll just hope senior boobs hook me up with a walkthrough

Download the attachment in the first post. The author "boops boops" included a couple of examples in the downloadable file that have be commented out.

[boops boops]

See post #1 in this thread:

nearly all the bitmaps we deal with are either 24 bits (digital photos, some drawing programs) or 32 bits (drawing programs with transparency). GDI+ converts 24 bit images internally to 32 bits anyway, so I have designed FastPix to work with 32 bits only. It makes the code simpler and opens up the possibility of processing bitmaps as Integer arrays, which are blindingly fast. FastPix includes a ConvertFormat method for converting bitmap pixel formats.

BB

[moti barski]

senior convertFormat glitched, before that there was another glitch and
walkthrough pliz

[Milk]

Moti, I propose that you are the glitch.

Imaging.PixelFormat.Alpha is not a pixel format it is a flag, there is not such thing as a bitmap with a format of Alpha.

The ConvertFormat() format parameter is optional you do not need to pass it, if you do pass it use one of the formats that start with Format32bpp.

You must convert the Bitmap before you pass it to the FastPix constructor not after.

PictureBox1.Image must contain a valid GDI Bitmap.

[moti barski]

so, it is a fluke if a bitmap work with the class, thanks milk now I get it

[boops boops]

Edit: follow Milk's advice. The next version of FastPix will make it a bit easier to avoid that mistake. BB

[formlesstree4]

so, it is a fluke if a bitmap work with the class, thanks milk now I get it

No fluke; it's pretty much spelled out how to make it work.

[moti barski]

and if I had wheels I'd be a wagon

[formlesstree4]

and if I had wheels I'd be a wagon

How does that even relate to this situation? You're merely making an analogy that has no reference to the subject at hand. I'm sorry but it wouldn't take very long to work with the code and produce the desired effect you want.

[sacramento]

Hi:

I had download your code but VB don't recognize fastpix...

Type 'Fastpix' is not defined

Any suggestion?

Thanks

[boops boops]

1. download the zip file
2. unzip it to obtain FastPix.vb
3. save the file wherever you like to keep your downloaded code.
4. in Visual Studio, right-click on your project name
5. select Add Existing Item
6. browse to find the FastPix.vb file and select it
7. now you can use Faspix in the project.

BB

[sacramento]

Hi:

Thanks for your answear...
I have one doubt her.e..your code could adapt to rotate images or graphics?

[boops boops]

Hi:

Thanks for your answear...
I have one doubt her.e..your code could adapt to rotate images or graphics?

It could be used for that in theory, but I doubt if it would be worth the effort. The GDI+ plus methods for rotation (Bitmap.RotateFlip, Graphics.RotateTransform etc.) seem pretty efficient to me. I suppose they use the same Math methods as you would use yourself on an array of pixels.

BB

[sacramento]

Hi:

Ok...thanks

[SaxxonPike]

I've been using a different method for about a year without fail. It doesn't involve marshalling anything.

I write this from memory, please excuse me if it is incorrect..

Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.Runtime.InteropServices
 
Public Class DirectBitmap
    
    Private Handle as GCHandle
    Public Readonly Pixels() as Int32
    Public Readonly Bitmap as Bitmap
    Public Readonly Width as Integer
    Public Readonly Height as Integer
    
    Public Sub New(NewWidth as Integer, NewHeight as Integer)
        Dim Area as Integer
        Width = NewWidth
        Height = NewHeight
        Area = Width * Height
        Redim Pixels(Area - 1)
        Handle = GCHandle.Alloc(Pixels, GCHandleType.Pinned)
        Bitmap = New Bitmap(Width, Height, 4 * Width, PixelFormat.Format32bppPArgb, Handle.AddrOfPinnedObject)
    End Sub
    
    Protected Overrides Sub Finalize()
        Bitmap = Nothing
        Handle.Free()
        Handle = Nothing
        Pixels = Nothing
        MyBase.Finalize()
    End Sub
End Class

[boops boops]

Hi SaxxonPike,

I compared the "pinned array" method with "lockbits" when I was developing FastPix. It appeared that the pixel processing speed was more or less identical for the two methods, but the instantiation time for the pinned array was much longer, regardless of the bitmap size. I was also uncertain whether the pinned array code might yield problems further down the line (compared to the well-tried lockbits) so I decided to leave it on the shelf.

It's easy to make mistakes when comparing performance, so now (with more experience) I should take a new look at it. Maybe I could try the code you have posted instead of my own version, which was based on a CodeProject example. So thanks for posting it.

Besides, the pinned array approach has significant advantages when you need to process the same bitmap over and over again. Unlike lockbits, you don't have to unlock the bitmap to get at the results so you only have to create the array once. There may also be some advantage to processing the pinned array in an Unsafe block in Csharp, but from what I have read I wouldn't expect it to make a spectacular difference.

BB

[SaxxonPike]

Hi SaxxonPike,

I compared the "pinned array" method with "lockbits" when I was developing FastPix. It appeared that the pixel processing speed was more or less identical for the two methods, but the instantiation time for the pinned array was much longer, regardless of the bitmap size. I was also uncertain whether the pinned array code might yield problems further down the line (compared to the well-tried lockbits) so I decided to leave it on the shelf.

My guess would be that the garbage collector has to make special provisions as it cannot do anything with a pinned object. It's really useful if it's something like a screen buffer that won't change for the duration of execution. I am currently using it for a game project and notice no significant slowdowns as a result of creating and disposing bitmaps created in this manner, but I haven't done performance testing extensively as you have.

Doesn't seem like I'm able to edit the code, after throwing it into VB I realized that "Bitmap" was a class name being used as a variable. Whoops The code should work otherwise (if you originally try it, all pixels will have value 0- completely transparent).

There may also be some advantage to processing the pinned array in an Unsafe block in Csharp, but from what I have read I wouldn't expect it to make a spectacular difference.

I thought about using the Unsafe block as I also work with C#; however, that might require special permissions for the end-user and a special configuration for the program. I'm not a big fan of this myself

[boops boops]

Doesn't seem like I'm able to edit the code, after throwing it into VB I realized that "Bitmap" was a class name being used as a variable. Whoops The code should work otherwise (if you originally try it, all pixels will have value 0- completely transparent).

Try putting square brackets round the identifier [Bitmap]. BB