Moxie Data Weblog - Blending Two Images Using GDIPlusX

Thursday, October 02, 2008

Blending Two Images Using GDIPlusX

After seeing a post on the Micrsoft forums. I set out to try and solve how to blend two images using GDI+. I could find little information on the web on how to solve this particular problem, so I came up with my own technique (with some excellent help from Craig Boyd).

Here is a sample blended image and the VFP / GDIPlusX code that I used to create it.

Paste this code into a PRG and run it. This code requires the GDIPlusX library from VFPX.

Local lcPict1, lcPict2

m.lcPict1 = Getpict()

If File(m.lcPict1)

m.lcPict2 = Getpict()

If File(m.lcPict2)

ImageAlphaBlend(m.lcPict1, m.lcPict2)

Endif

**********************************************************

Function ImageAlphaBlend(tcPictLeft, tcPictRight)

**********************************************************

Local loColorMatrix As xfcCOlorMatrix

Local loImageLeft As xfcImage

Local loImageRight As xfcImage

Local loBitmapPart As xfcBitmap

Local loBitmapLeft As xfcBitmap

Local laImageAttribs[1]

Local loGfxLeft As xfcGraphics

Local loGfxPart As xfcGraphics

Local loGfxScreen As xfcGraphics

Local lnAlphaSteps, lnBlendPercentage, lnWidthOpaque, lnStep, lnHeightImage, lnLeftStart

** Sets the number of Alpha blend steps used to render the blend.

** The max is 256. lower steps equals lower quality, but higher speed

m.lnAlphaSteps = 128

** Sets the percentage of the image that is blended

m.lnPercentageBlend = .75

Dimension laImageAttribs[m.lnAlphaSteps]

** Requires the GDIPlusX library (version 1.20 beta)

** http://www.codeplex.com/VFPX/Release/ProjectReleases.aspx?ReleaseId=15083

Do (Locfile("SYSTEM.APP"))

With _Screen.System.Drawing

m.loImageRight = .Image.FromFile(m.tcPictLeft)

m.loImageLeft = .Image.FromFile(m.tcPictRight)

** Force the left image to be the same size as the right image

m.loBitmapLeft = .Bitmap.New(m.loImageRight.Width, m.loImageRight.Height)

m.loGfxLeft=.Graphics.FromImage(m.loBitmapLeft)

m.loGfxLeft.Clear(.Color.Transparent)

m.loGfxLeft.DrawImage(m.loImageLeft,0,0,m.loBitmapLeft.Width,m.loBitmapLeft.Height)

m.lnWidthOpaque = m.loImageRight.Width * (1 - m.lnPercentageBlend) / 2

m.lnWidthPart = Ceiling((m.loBitmapLeft.Width-m.lnWidthOpaque*2)/m.lnAlphaSteps)

m.loBitmapPart = .Bitmap.New(m.lnWidthPart, m.loBitmapLeft.Height)

m.loGfxPart=.Graphics.FromImage(m.loBitmapPart)

m.loGfxPart.Clear(.Color.Transparent)

** Pre-fill ImageAttributes with Alpha ColorMatrix blend for performance

** The biggest advantage to doing this is if you were processing multiple

** set of images at a time, which we aren't doing here.

m.loColorMatrix=.Imaging.ColorMatrix.New()

For m.lnCurrentStep = 1 To m.lnAlphaSteps

laImageAttribs[m.lnCurrentStep] = .Imaging.ImageAttributes.New()

m.loColorMatrix.Matrix33 = m.lnCurrentStep/m.lnAlphaSteps

laImageAttribs[m.lnCurrentStep].SetColorMatrix(m.loColorMatrix)

Endfor

** Adjust these for preferred image quality vs. speed

*m.loGfxLeft.InterpolationMode = .Drawing2D.InterpolationMode.Default

*m.loGfxLeft.CompositingQuality = .Drawing2D.CompositingQuality.Default

*m.loGfxLeft.SmoothingMode = .Drawing2D.SmoothingMode.Default

** Use integers instead of floats for performance

m.loGfxLeft.UsePrecision = .F.

** Minor speed increase accessing this property once

m.lnHeightImage = m.loImageRight.Height

For m.lnCurrentStep = 1 To m.lnAlphaSteps

m.lnLeftStart = m.lnCurrentStep*m.lnWidthPart + m.lnWidthOpaque

** Draw partial right image to part

m.loGfxPart.DrawImage(m.loImageRight, ;

0,0,m.lnWidthPart,m.lnHeightImage, ;

m.lnLeftStart,0,m.lnWidthPart,m.lnHeightImage, ;

.GraphicsUnit.Pixel)

** Draw part to left image with Alpha blend

m.loGfxLeft.DrawImage(m.loBitmapPart, ;

m.lnLeftStart,0,m.lnWidthPart,m.lnHeightImage, ;

0,0,m.lnWidthPart,m.lnHeightImage, ;

.GraphicsUnit.Pixel, ;

laImageAttribs[m.lnCurrentStep])

Endfor

** Draw last opaque part of right image

m.loGfxLeft.DrawImage(m.loImageRight, ;

m.loImageRight.Width-m.lnWidthOpaque, 0, m.lnWidthOpaque, m.lnHeightImage, ;

.GraphicsUnit.Pixel)

** Render to the screen

m.loGfxScreen = .Graphics.FromHWnd(_Screen.HWnd)

m.loGfxScreen.Clear(.Color.White)

m.loGfxScreen.DrawImage(m.loBitmapLeft,0,0,1024,768)

** Or you can save it to a file

**m.loBitmapLeft.Save("MyBlendedImage.png")

Endwith

Return

Endfunc

Thursday, October 02, 2008 3:43:52 PM (Eastern Daylight Time, UTC-04:00)

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