APIGettingImageInformation

Getting Image File Information with GDI32

While it is possible to open and read any image file as a sequential file to find the image width and height , it may be easier to use the GDI32 GetObjectA . GetObjectA retrieves information for all bitmaps in memory. Load the image first with GDIPlus with a call to GdipCreateBitmapFromFile . Once the image is loaded, call GetObjectA to retrieve information. This code is based in part upon Alyce Watson's demo Sprite in a Box in the Liberty BASIC Newsletter, Issue #108 API Graphics Series . The code also uses Dan Teel's demo Load Any Image with GDIPlus .

Two structs are needed. The first is for the GetObjectA code. The struct holds the bitmap information.

 Struct ImageInfo, _ 
 imgType as Long, _ 
 imgWidth as Long, _ 
 imgHeight as Long, _ 
 imgWidthBytes as Long, _ 
 imgPlanes as Word, _ 
 imgBitsPixel as Word, _ 
 imgBits as Long 

The second struct is for the GdipCreateBitmapFromFile code.

 Struct doubleWord, a as uLong 

Once the image is loaded and GetObjectA is called, the ImageInfo struct will contain the bitmap. Copy the width and height information from the struct to numeric variables.

 imgWidth = ImageInfo.imgWidth.struct 
 imgHeight = ImageInfo.imgHeight.struct 

The advantages to loading an image with GdipCreateBitmapFromFile and then calling GetObjectA to find the width and height of the image are

• 1. No parsing of the image extension is needed to identify the image format
• 2. No complicated math formulas are needed to extract the width and height of the format
• 3. No error is given when trying to access a file path longer than 128 characters

When the image is no longer needed, delete the image from memory with DeleteObject .

 Call DeleteObject hImage 
 
 Sub DeleteObject hImage 
 CallDLL #gdi32, "DeleteObject", _ 
 hImage as uLong, _ 
 result as Long 
 End Sub 

Demo to Load an Image with GdipCreateBitmapFromFile and Find Dimensions with GetObjectA

 
 ' Extension variable for Filedialog 
 ' Valid image formats are bmp, gif, ico, jpg, png, and tiff 
 iExt$ = "*.bmp;*.gif;*.ico;*.jpg;*.png;*.tiff" 
 
 ' Variables to hold the width and height of the image 
 imageWidth = 0 
 imageHeight = 0 
 
 ' Struct necessary for loading an image with GDIPlus 
 Struct doubleWord, a as uLong 
 
 ' Struct necessary for returning image file information 
 Struct ImageInfo, _ 
 imgType as Long, _ 
 imgWidth as Long, _ 
 imgHeight as Long, _ 
 imgWidthBytes as Long, _ 
 imgPlanes as Word, _ 
 imgBitsPixel as Word, _ 
 imgBits as Long 
 
 ' Design a GUI to host the image 
 WindowWidth = 800 
 WindowHeight = 600 
 UpperLeftX = Int((DisplayWidth - WindowWidth) / 2) 
 UpperLeftY = Int((DisplayHeight - WindowHeight) / 2) 
 
 ' Design a graphicbox to display the image 
 Stylebits #main.g, 0, _WS_BORDER, 0, 0 
 Graphicbox #main.g, 0, 0, 792, 580 
 
 Open "Getting the Image Width and Height with GetObjectA" for Window_nf as #main 
 #main "Trapclose [closeApp]" 
 #main "Font Verdana 10 Bold" 
 hMain = hWnd(#main) 
 hG = hWnd(#main.g) 
 #main.g "Down" 
 ' Load an image file 
 Filedialog "Image to Load", iExt$, imagePathFile$ 
 ' Load the image using GDIPlus, hImage is the returned handle to the bitmap in memory 
 hImage = LoadImgFromFile(imagePathFile$) 
 ' Get the bitmap information using GetObjectA 
 imageDimen$ = ImageDimensions$(hImage) 
 imageW = Val(Word$(imageDimen$, 1, Chr$(0))) 
 imageH = Val(Word$(imageDimen$, 2, Chr$(0))) 
 ' Load the bitmap in memory 
 Loadbmp "pic", hImage 
 ' Draw the image using native LB command Drawbmp 
 #main.g "Drawbmp pic 10 10; Flush" 
 ' Resize the graphicbox to the size of the image 
 #main.g "Locate 0 0 ";imageW + 20;" ";imageH + 20 
 #main "Refresh" 
 ' Give the width and height of the image 
 msg$ = "Image Dimensions";Chr$(10);Chr$(13); _ 
 "Width: ";imageW;" pixels";Chr$(10);Chr$(13); _ 
 "Height: ";imageH;" pixels";Chr$(10);Chr$(13) 
 Notice msg$ 
 Wait 
 
 [closeApp] 
 ' Unload the native LB bitmap 
 Unloadbmp "pic" 
 ' Release memory from GDIPlus loaded image 
 Call DeleteObject hImage 
 Close #main 
 End 
 
 Function ImageDimensions$(hImage) 
 lStruct = Len(ImageInfo.struct) 
 CallDLL #gdi32, "GetObjectA", _ 
 hImage as uLong, _ 
 lStruct as Long, _ 
 ImageInfo as struct, _ 
 result as Long 
 imgWidth = ImageInfo.imgWidth.struct 
 imgHeight = ImageInfo.imgHeight.struct 
 ImageDimensions$ = Str$(imgWidth);Chr$(0);Str$(imgHeight) 
 End Function 
 
 Function wChar$(string$) 
 For i = 1 to Len(string$) 
 wChar$ = wChar$ + Mid$(string$, i, 1) + chr$(0) 
 Next i 
 wChar$ = wChar$ + Chr$(0) + Chr$(0) 
 End Function 
 
 Function LoadImgFromFile(picFile$) 
 Open "gdiplus.dll" for dll as #gdip 
 gdistart$=Chr$(1) 
 For i = 1 to 15 
 gdistart$ = gdistart$ + Chr$(0) 
 Next i 
 Calldll #gdip,"GdiplusStartup", _ 
 doubleWord as struct, _ 
 gdistart$ as Ptr, _ 
 status as uLong 
 token=doubleWord.a.struct 
 If status <> 0 Then 
 LoadImgFromFile = 0 
 Else 
 wFileLoc$=wChar$(picFile$) 
 Calldll #gdip,"GdipCreateBitmapFromFile", _ 
 wFileLoc$ as Ptr, _ 
 doubleWord as struct, _ 
 status as uLong 
 hPic = doubleWord.a.struct 
 If status <>0 then 
 LoadImgFromFile=0 
 Else 
 CallDLL #gdip,"GdipCreateHBITMAPFromBitmap", _ 
 hPic as uLong, _ 
 doubleWord as struct, _ 
 0 as uLong, _ 
 status as uLong 
 hImage=doubleWord.a.struct 
 If status <> 0 Then 
 LoadImgFromFile = 0 
 Else 
 LoadImgFromFile = hImage 
 End if 
 CallDLL #gdip,"GdipDisposeImage", _ 
 hPic as uLong, _ 
 result as uLong 
 End If 
 CallDLL #gdip,"GdiplusShutdown", _ 
 token as uLong, _ 
 result as uLong 
 End If 
 Close #gdip 
 End Function 
 
 Sub DeleteObject hImage 
 CallDLL #gdi32, "DeleteObject", _ 
 hImage as uLong, _ 
 result as Long 
 End Sub 

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