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Preface

Years after the previous version, I can tell that the article has survived its author, and even if my opinion on the limits of this library has not changed, an update was really necessary.

Thank you very much to all the people that gave their contribution to this new release, with hundreds of small and big enhancements, my role was mainly to put all the pieces together.

Introduction & License

CxImage is a C++ class that can load, save, display, and transform images in a very simple and fast way.

The class CxImage is free; as for the TIFF, JPEG, PNG and ZLIB libraries : "If you use this source code in a product, acknowledgement is not required but would be appreciated."

CxImage is open source and licensed under the zlib license . In a nutshell, this means that you can use the code however you wish, as long as you don't claim it as your own.

What's New in Version 6.00

The complete list of bugfixes and enhancements is reported in the documentation, (see \doc\cximage_history.htm, or this link). Here I will highlight some of the new features.

An application written with CxImage version 5.99 should work also with the new version; the interface of few methods is different, normally because of new parameters, but the default behaviour is the same.

The applications linked with the old DLL will not work with the new one; but if necessary you can edit the declarations, or add new overloads, and revert to the old interface for the DLL. An issue to take care is ENUM_CXIMAGE_FORMATS: in the old version the CXIMAGE_FORMAT_... can change the value, depending on the supported formats enabled by the corresponding CXIMAGE_SUPPORT_... switch. In the new version, CXIMAGE_FORMAT_... are assigned to unique values. Static methods like GetNumTypes, GetTypeIdFromName, GetTypeIdFromIndex, GetTypeIndexFromId will help the application to manage the new policy.

File Formats & Linked C Libraries

CxImage works with the latest version of these libraries: Zlib (1.2.3), Jasper ( 1.900.1), LibMNG (1.0.10), LibPNG (1.2.24). LibTIFF 3.8.2 can be linked with CxImage, but the version included in the CxImage distribution (3.5.7, patched) can read images with OJPEG compression, or with non standard bit per samples. The choice is up to you.

The j2k library (now openjpeg), and the associated class CxImageJ2K, have been removed from the project. JPEG2000 images are supported through Jasper and CxImageJAS.

CxImage 6.00 includes a new class (CxImageRAW) and a new library (LibDCR) to read RAW images from digital cameras; common file extension are: RAW, CRW, NEF, CR2, DNG, ORF, ARW, ERF, 3FR, DCR, X3F, MEF, RAF, MRW, PEF, SR2. LibDCR is based on Dave Coffin's dcraw.c; and offers the same features of the original dcraw application (see the "dcr.dsw" project included in the \raw directory). The restricted features under the GPL Version 2 are disabled; please read the license terms in "libdcr.h" before enabling the restricted code.

CxImageRAW implements the basic functions to decode the image, the only available option controlled by SetCodecOption, is about the interpolation quality (DECODE_QUALITY_LIN=0, DECODE_QUALITY_VNG=1, DECODE_QUALITY_PPG=2, DECODE_QUALITY_AHD=3).

CxImagePNG has been improved to read and write all of the PNG_COLOR_TYPE_... combinations. PNGs with a "pixel depth" more that 8 bits per channel will be converted down to 8 bits, this is the major limit in CxImage.

CxImageGIF: better support for reading animated GIF, now can decode all frames in a single pass, if enabled with SetRetreiveAllFrames. The CxImage demo implements this option, and shows how to play an animated GIF (when the program asks "File with N images. Read all?", select "Cancel").

CxImageBMP: reads and writes 32 bit images (with alpha layer).
CxImageICO: reads and writes Vista (PNG) icons; and added support for writing multipage icons.
CxImageMNG: reads MNGs with alpha layer.
CxImageSKA: new class for SKA image format, used in some video rental application.

CxImageJPG: new options for the JPEG format subsampling (ENCODE_SUBSAMPLE_422, ENCODE_SUBSAMPLE_444), default is 4:1:1 (high), can be set to 4:2:2 (medium) or 4:4:4 (none).

The next table shows the different amount of artifacts in the compressed image, using to different subsampling. 4:4:4 subsampling is useful in images with sharp edges, to reduce the typical blurring effect of the JPG compression.

original image	JPG image and artefacts, quality 75, subsampling 4:1:1	JPG image and artefacts, quality 75, subsampling 4:4:4

Portability

The class and the projects have been tested with different compilers, from Microsoft VC++6 to VC++2008, with Borland C++ Builder 3 and 6, and partially with wxDev-C++ and MinGW.

UNICODE and non-UNICODE configurations are provided for all the libraries (thanks to Eric Jesover).

A light version (cximage600_lite) without the C libraries and with a small demo is provided for the first time users, or as a basic template, without the clutter of the full demo project.

The console (\demo2) and the CxImageCrtDll projects can be built with VC++Express2005 and the Microsoft Platform SDK. If you get linker errors like "unresolved external...", check if all the C libraries have been compiled (set the correct project dependencies), or add the gdi32.lib and user32.lib modules to the Linker\Input\Additional Dependencies property.

CxImage works also with Pocket PC 2003; a working version and demo (cximage600_ce) are provided for the VC++2005 compiler (thanks to Vincent Richomme). For the old embedded VC compilers, the main limit was the support for exception handling. To overcome this problem, the try, throw and catch statements have been replaced with 3 macros (defined in ximadef.h), and with the definition of CXIMAGE_SUPPORT_EXCEPTION_HANDLING; in this way it is possible to build the library without exception handling support. Maybe the solution is not so elegant, but the impact on the source code is minimal when exception handling is disabled, while there are no changes in case of exception handling enabled.

The compatibility between little-endian and big-endian platforms, for the built in formats (bmp, ico, tga, pcx, gif, ska) is handled by ntohs and ntohl.

Demo

Almost all the new features can be tested in the main CxImage demo application. The demo is just a test bench, even if it offers some nice features, it is not intended to be a serious application.

CQuantizer : the class is used with the DecreaseBpp menu. In the previous version there was a rounding error, clearly visible when in some case the white colour (255,255,255) was converted to (254,254,254). In the new release this error has been fixed.
Copy/Paste : now pastes also metafile pictures (for example, from Office applications). The demo internally uses a custom clipboard format, to test the Dump/Undump methods.
Copy works on the active selection, use \CxImage\Remove Selection to copy the full image.
FloodFill : (\View\Tools\Flood Fill) with a floating dialog, you can test the FloodFill colour, tolerance, opacity, and selection. The case with opacity = 0 and selection enabled acts as a "magic wand".
Graph data extraction : (\Filters\graph data extraction) extracts the numeric data from graphs (acquired from scanners or downloaded from the internet). The converted values are pasted into the clipboard, and can be saved to text or Excel files.

Data Extraction dialog and results
RedEyeRemove : (\Filters\Non Linear\Remove Red Eye) removes the red-eye effect that frequently occurs in pictures. You must select the region around the pupil, where the function will filter the red channel. The selection can also be rectangular, or including part of the iris: the filter works on a circular region centred on the selection.

original image
selection around the pupil
result after RedEyeRemove
SelectiveBlur / UnsharpMask : these non linear filters increase the image quality. SelectiveBlur removes the "granular" noise (jpeg artefacts, or digital camera noise) preserving the details, UnsharpMask enhances the details without adding noise in the "flat" regions.
Custom linear filters : (\Filters\Linear\Custom) a small graphic interface to test new kernels for the Filter function (thanks to Priyank Bolia).
Histogram : (\Colors\Histogram\...) many menus are available to test HistogramStretch with different approaches (0 = luminance, 1 = linked channels , 2 = independent channels); the threshold parameter increases the robustness of the algorithm in case of noisy images. "Half Saturation" and "Full Saturation" test the combination of ConvertColorSpace, Histogram, and Saturate, to stretch the histogram in the YUV colorspace.

original image
+ HistogramStretch(2,0.005f)
+ "Half saturation"
Thresholding : ( \Colors\Threshold... and \Colors\Adaptive Threshold). OptimalThreshold is a new method to find the optimal threshold for image binarization, the available algorithms are:
1 = Otsu;
2 = Kittler & Illingworth;
3 = maximum entropy;
4 = potential difference;
0 = average all methods (default, and used in the demo);
The option "preserve colors less than the threshold" will test Threshold2, useful to filter colored images with a noisy background, the result will be a colored image with a uniform background.
AdaptiveThreshold is an application of OptimalThreshold to build a variable threshold mask. AdaptiveThreshold is useful in case of images with a non uniform lightness, where a single threshold can't be optimal for the whole image; but in general it will give bad results if the parameters are not well tuned.

original image

OptimalThreshold + Threshold

AdaptiveThreshold
Add shadow : (\Filters\Add Shadow...) this menu is a small example on how the simple CxImage methods (selections, GaussianBlur, Mix) can be combined to obtain a common effect.

purple shadow on white background
black shadow on red background
Text smoothing : DrawStringEx implements a new option, through CXTEXTINFO::smooth, that can be tested with the text tool (\View\Tools\Text), checking the "antialias" option.
A similar effect can be obtained in post processing with TextBlur (\Filters\Non Linear\Text Blur): a non linear filter that works only on diagonal or round edges, without affecting vertical or horizontal lines. In the next table there is a comparison between different smoothing methods:

DrawStringEx without smoothing
DrawStringEx with smoothing

post processing with TextBlur
post processing with a linear 3x3 "soften" Filter

CxImage Structure

In the vertical hierarchy of the library, CxImage stays on the top of the other modules, it's not a clean OOP approach, but the result was good since the first release and now it's too late to change again. Anyway you can always use the derived classes to perform the format specific operations, like for CxImageTIF to save multipage TIFFs.

The glue to connect all the modules and the C libraries is CxFile, a virtual class that provides the standard methods to access the data from a file on the disk or in memory.

A Cximage object is basically a bitmap, with the addition of some member variables to store useful information:

 class CxImage
  {
  ...
  protected:
  void* pDib;            //contains the header, the palette, the pixels
  BITMAPINFOHEADER head; //standard header
  CXIMAGEINFO info;      //extended information
  BYTE* pSelection;      //selected region
  BYTE* pAlpha;          //alpha channel
  CxImage** ppLayers;     //generic layers
  CxImage** ppFrames;     //frames for animation
  }

CxImage::head is the bitmap header and CxImage::pDib is a normal bitmap (as you can see in the implementation of CxImageBMP::Encode).

CxImage::info is a handy container of many information shared between different formats, and for all the member functions.

typedef struct tagCxImageInfo {
    DWORD   dwEffWidth;       //DWORD aligned scan line width
    BYTE*   pImage;           //THE IMAGE BITS
    void*   pGhost;           //if this is a ghost, pGhost point to the body
    DWORD   dwType;           //original image format
    char    szLastError[256]; //debugging
    long    nProgress;        //monitor
    long    nEscape;          //escape
    long    nBkgndIndex;      //used for GIF, PNG, MNG
    RGBQUAD nBkgndColor;      //used for RGB transparency
    BYTE    nQuality;         //used for JPEG
    long    nFrame;           //used for TIF, GIF, MNG : actual frame
    long    nNumFrames;       //used for TIF, GIF, MNG : total number of 
                              //frames
    DWORD   dwFrameDelay;     //used for GIF, MNG
    long    xDPI;             //horizontal resolution
    long    yDPI;             //vertical resolution
    RECT    rSelectionBox;    //bounding rectangle
    BYTE    nAlphaMax;        //max opacity (fade)
    bool    bAlphaPaletteEnabled;  //true if alpha values in the palette are 
                              // enabled.
    bool    bEnabled;         //enables the painting functions
    long    xOffset;
    long    yOffset;
    DWORD   dwEncodeOption;   //for GIF, TIF : 0=def.1=unc,2=fax3,3=fax4,
                              // 4=pack,5=jpg
    RGBQUAD last_c;           //for GetNearestIndex optimization
    BYTE    last_c_index;
    bool    last_c_isvalid;
    long    nNumLayers;
    DWORD   dwFlags;
} CXIMAGEINFO;

A CxImage object is also a set of layers. The buffers in each layer are allocated only when necessary.

CxImage::pDib is the background image. CxImage::pAlpha is the transparency layer. CxImage::pSelection is the selection layer, used to create regions of interest for image processing. Over these 3 specific planes, you can add other generic layers, stored in CxImage::ppLayers. The generic layers are full CxImage objects, so you can build complex structures of nested layers. CxImage::ppFrames is reserved for animated images (GIF)

CxImage Class Members & Operations

CxImage is documented using Doxygen , however for historical reasons, many uncommon features are still undocumented. The class members reference, together with release history, and license, can be found here

Supported Formats and Options

The whole library is quite big, in the main header file ximcfg.h you'll find the switches to enable or disable a specific graphic format or feature. Each JPG, PNG and TIFF library adds about 100KB to the final application, while the CxImage impact is about 50KB. So you should support and link only the formats that your application really needs.

formats	#define	required libraries	size [Kbyte]
BMP GIF ICO TGA PCX WBMP WMF SKA	`CXIMAGE_SUPPORT_BMP CXIMAGE_SUPPORT_GIF CXIMAGE_SUPPORT_ICO CXIMAGE_SUPPORT_TGA CXIMAGE_SUPPORT_PCX CXIMAGE_SUPPORT_WBMP CXIMAGE_SUPPORT_WMF CXIMAGE_SUPPORT_SKA`	built in	24
JPEG	`CXIMAGE_SUPPORT_JPG`	jpeg	88
PNG	`CXIMAGE_SUPPORT_PNG`	png, zlib	104
MNG	`CXIMAGE_SUPPORT_MNG`	mng, zlib, jpeg	148
TIFF	`CXIMAGE_SUPPORT_TIF`	tiff, zlib, jpeg	124
JBIG	`CXIMAGE_SUPPORT_JBG`	jbig	28
PNM,PPM,PGM RAS	`CXIMAGE_SUPPORT_PNM CXIMAGE_SUPPORT_RAS`	jasper	176
JPEG-2000	`CXIMAGE_SUPPORT_JP2 CXIMAGE_SUPPORT_JPC CXIMAGE_SUPPORT_PGX`	jasper	176
RAW	`CXIMAGE_SUPPORT_RAW`	libdcr	132

Option	#define	Size [Kbyte]
CxImage core	all switches off	20
geometric transformations	`CXIMAGE_SUPPORT_TRANSFORMATION`	16
image processing	`CXIMAGE_SUPPORT_DSP`	24
drawing and windows specific functions	`CXIMAGE_SUPPORT_WINDOWS`	12
transparency	`CXIMAGE_SUPPORT_ALPHA`	4
selections	`CXIMAGE_SUPPORT_SELECTION`	4
multiple layers	`CXIMAGE_SUPPORT_LAYERS`	< 4
graphic formats conversion	`CXIMAGE_SUPPORT_DECODE CXIMAGE_SUPPORT_ENCODE`	< 4
interpolation functions	`CXIMAGE_SUPPORT_INTERPOLATION`	< 4
exception handling	`CXIMAGE_SUPPORT_EXCEPTION_HANDLING`	< 4

Using CxImage in your Projects

The CxImgLib.dsw workspace shows the libraries required to build an application (demo.exe) including almost all the features and the formats available in CxImage. You must compile all the libraries before you can link the final application.
In the same workspace you'll find the projects to build different libraries and applications:

CxImage : cximage.lib - static library
CxImageCrtDll : cximagecrt.dll - DLL not using mfc
CxImageMfcDll : cximage.dll - DLL using mfc
Demo : demo.exe - program linked with cximage.lib and the C libraries
DemoDll : demodll.exe - program linked with cximagecrt.dll
libdcr,jasper,jbig,jpeg,png,tiff,zlib : static C libraries

Building the projects will need some minutes to complete. When everything is done, select the demo project and launch the application.

CxImgLib.dsw

To use CxImage in your project, you must edit these settings:

Project Settings
 |- C/C++
 |   |- Code Generation
 |   |   |- Use run-time library : Multithreaded DLL (must be the same for 
 |   |   |  all the linked libraries)
 |   |   |- Struct member alignment : must be the same for all the linked 
 |   |   |  libraries
 |   |- Precompiled headers : not using precompiled headers
 |   |- Preprocessor
 |       |- Additional Include Directories:  ..\cximage
 |- Link
    |- General
        |- Object/library modules: ../png/Debug/png.lib  
                                   ../raw/Debug/libdcr.lib
                                   ../jpeg/Debug/jpeg.lib 
                                   ../zlib/Debug/zlib.lib 
                                   ../tiff/Debug/tiff.lib
                                   ../jasper/Debug/jasper.lib
                                   ../cximage/Debug/cximage.lib  ...

In your source code you must add #include "ximage.h"

Note: don't mix debug and release modules; each configuration must use its respective library modules.

Adding your Custom Functions in CxImage

Writing a new function for image processing is not so hard with CxImage. Here I'm going to describe CxImage::Jitter — it's very simple but it shows many aspects to take care of when you work inside CxImage. The first thing, of course, is the declaration : bool Jitter(long radius=2); in the CXIMAGE_SUPPORT_DSP section of ximage.h, you can declare the function everywhere in the public scope of the class. And now the definition:

bool CxImage::Jitter(long radius)
{
    // check if the image is valid, this should be always the first line in 
    // the function 
    if (!pDib) return false;
    
    // local variables
    long nx,ny;
    
    // temporary image to store the partial results of the algorithm
    CxImage tmp(*this,pSelection!=0,true,true);
    
    // limit the effects of the functions only in the smallest rectangle that
    // holds the selected region (defined with the Selection...() functions ),
    // this will speed up the loops.
    long xmin,xmax,ymin,ymax;
    if (pSelection){
        xmin = info.rSelectionBox.left; xmax = info.rSelectionBox.right;
        ymin = info.rSelectionBox.bottom; ymax = info.rSelectionBox.top;
    } else {
        xmin = ymin = 0;
        xmax = head.biWidth; ymax=head.biHeight;
    }
    
    // main loop : scan the image in vertical direction
    for(long y=ymin; y <ymax; y++){
    
        // monitor the progress of the loops
        info.nProgress = (long)(100*y/head.biHeight);
    
        // let the application a way to exit quickly
        if (info.nEscape) break;
    
        // main loop : scan the image in horizontal direction
        for(long x=xmin; x<xmax; x++){
    
        // if the feature is enabled, process only the pixels inside the 
        // selected region
#if CXIMAGE_SUPPORT_SELECTION
            if (SelectionIsInside(x,y))
#endif //CXIMAGE_SUPPORT_SELECTION
            {
                // main algorithm
                nx=x+(long)((rand()/(float)RAND_MAX - 0.5)*(radius*2));
                ny=y+(long)((rand()/(float)RAND_MAX - 0.5)*(radius*2));
                if (!IsInside(nx,ny)) {
                    nx=x;
                    ny=y;
                }

                // save the result in the temporary image.
                // if you can, use PixelColor only for 24 bpp images,
                // and PixelIndex for 8, 4 and 1 bpp images : it's faster
                if (head.biClrUsed==0){
                    tmp.SetPixelColor(x,y,GetPixelColor(nx,ny));
                } else {
                    tmp.SetPixelIndex(x,y,GetPixelIndex(nx,ny));
                }

                // if the feature is enabled, process also the pixels 
                // in the alpha layer
#if CXIMAGE_SUPPORT_ALPHA
                tmp.AlphaSet(x,y,AlphaGet(nx,ny));
#endif //CXIMAGE_SUPPORT_ALPHA

            }
        }
    }

    // save the result and exit
    Transfer(tmp);
    return true;
}

Examples: How to ...

... Convert from One Format to Another

CxImage  image;
// bmp -> jpg


image.Load("image.bmp", CXIMAGE_FORMAT_BMP);
if (image.IsValid()){
    if(!image.IsGrayScale()) image.IncreaseBpp(24);
    image.SetJpegQuality(80);
    image.Save("image.jpg",CXIMAGE_FORMAT_JPG);
}
// png -> tif


image.Load("image.png", CXIMAGE_FORMAT_PNG);
if (image.IsValid()){
    image.Save("image.tif",CXIMAGE_FORMAT_TIF);
}

... Load an Image Resource

//Load the resource IDR_PNG1 from the PNG resource type


CxImage* newImage = new CxImage();
newImage->LoadResource(FindResource(NULL,MAKEINTRESOURCE(IDR_PNG1),
                       "PNG"),CXIMAGE_FORMAT_PNG);

//Load the resource IDR_JPG1 from DLL




CxImage* newImage = new CxImage();
HINSTANCE hdll=LoadLibrary("imagelib.dll");

if (hdll){
    HRSRC hres=FindResource(hdll,MAKEINTRESOURCE(IDR_JPG1),"JPG");
    newImage->LoadResource(hres,CXIMAGE_FORMAT_JPG,hdll);
    FreeLibrary(hdll);
}

//Load a bitmap resource;

HBITMAP bitmap = ::LoadBitmap(AfxGetInstanceHandle(),
                              MAKEINTRESOURCE(IDB_BITMAP1)));
CxImage *newImage = new CxImage();
newImage->CreateFromHBITMAP(bitmap);

... Decode an Image from Memory

CxImage image((BYTE*)buffer,size,image_type);

CxMemFile memfile((BYTE*)buffer,size);
CxImage image(&memfile,image_type);

CxMemFile memfile((BYTE*)buffer,size);
CxImage* image = new CxImage();
image->Decode(&memfile,type);

... Encode an Image in Memory

long size=0;
BYTE* buffer=0;
image.Encode(buffer,size,image_type);
...
image.FreeMemory(buffer);

CxMemFile memfile;
memfile.Open();
image.Encode(&memfile,image_type);
BYTE* buffer = memfile.GetBuffer();
long size = memfile.Size();
...
image.FreeMemory(buffer);

... Create a Multipage TIFF

CxImage *pimage[3];
pimage[0]=&image1;
pimage[1]=&image2;
pimage[2]=&image3;

FILE* hFile;
hFile = fopen("multipage.tif","w+b");

CxImageTIF multiimage;
multiimage.Encode(hFile,pimage,3);

fclose(hFile);

FILE* hFile;
hFile = fopen("c:\\multi.tif","w+b");

CxImageTIF image;
image.Load("c:\\1.tif",CXIMAGE_FORMAT_TIF);
image.Encode(hFile,true);
image.Load("c:\\2.bmp",CXIMAGE_FORMAT_BMP);
image.Encode(hFile,true);
image.Load("c:\\3.png",CXIMAGE_FORMAT_PNG);
image.Encode(hFile);

fclose(hFile);

... Copy/Paste an Image

//copy

HANDLE hDIB = image->CopyToHandle();
if (::OpenClipboard(AfxGetApp()->m_pMainWnd->GetSafeHwnd())) {
    if(::EmptyClipboard()) {
        if (::SetClipboardData(CF_DIB,hDIB) == NULL ) {
            AfxMessageBox( "Unable to set Clipboard data" );
}    }    }
CloseClipboard();


//paste

HANDLE hBitmap=NULL;
CxImage *newima = new CxImage();
if (OpenClipboard()) hBitmap=GetClipboardData(CF_DIB);
if (hBitmap) newima->CreateFromHANDLE(hBitmap);
CloseClipboard();

... Display a File in a Picture Box

HBITMAP m_bitmap = NULL;
CxImage image("myfile.png", CXIMAGE_FORMAT_PNG);
...
CDC* hdc = m_picture.GetDC();
HBITMAP m_bitmap = image.MakeBitmap(hdc->m_hDC);

HBITMAP hOldBmp = m_picture.SetBitmap(m_bitmap);
if (hOldBmp) DeleteObject(hOldBmp);
if (hdc->m_hDC) m_picture.ReleaseDC(hdc);
...
if (m_bitmap) DeleteObject(m_bitmap);

History and Credits

Starting form my CxDib class, that implements memory DIBs only, I tried to add some members to read images from files. Looking for a solution, I found a nice MFC class named CImage on the net, release 1.4 (1998). CImage supports BMP, GIF, PNG and JPG, but suffers many little bugs and uses a complex class structure, so I decided to strip it to the base and merge CxDib with the CImage philosophy, to obtain the new CxImage class. Also I updated the libraries for JPG, PNG and ZLIB.

With CxImage it is very easy to add new image types, so I added the TIFF library (rev. 6) and a minimal support for ICONs, MNG, TGA and PCX. Finally I added some specific functions to obtain an image from global HANDLEs (windows clipboard) and objects (windows resources). This is the story until the early release, the following is written in the documentation.

Thanks to Troels Knakkergaard for his precious work in the earlier versions of CxImage, Rajiv Ramachandran for CTwain code; to Abe for multi page tiffs code; to Chris Shearer Cooper for memory file suggestions and code; to Brent Corkum for BCMenu code.

More specific credits and disclaimers are in every header file of each library.

License

This article, along with any associated source code and files, is licensed under The zlib/libpng License

About the Author

Davide Pizzolato

Supporter

Location:

Italy

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