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wxImage

This class encapsulates a platform-independent image. An image can be created from data, or using wxBitmap::ConvertToImage. An image can be loaded from a file in a variety of formats, and is extensible to new formats via image format handlers. Functions are available to set and get image bits, so it can be used for basic image manipulation.

A wxImage cannot (currently) be drawn directly to a wxDC. Instead, a platform-specific wxBitmap object must be created from it using the wxBitmap::wxBitmap(wxImage,int depth) constructor. This bitmap can then be drawn in a device context, using wxDC::DrawBitmap.

One colour value of the image may be used as a mask colour which will lead to the automatic creation of a wxMask object associated to the bitmap object.

Alpha channel support

Starting from wxWidgets 2.5.0 wxImage supports alpha channel data, that is in addition to a byte for the red, green and blue colour components for each pixel it also stores a byte representing the pixel opacity. The alpha value of 0 corresponds to a transparent pixel (null opacity) while the value of 255 means that the pixel is 100% opaque.

Unlike the RGB data, not all images have the alpha channel and before using GetAlpha you should check if this image contains alpha value with HasAlpha. In fact, currently only images loaded from PNG files with transparency information will have alpha channel but support for it will be added to the other formats as well (as well as support for saving images with alpha channel which is not still implemented either).

Available image handlers

The following image handlers are available. wxBMPHandler is always installed by default. To use other image formats, install the appropriate handler with wxImage::AddHandler or wxInitAllImageHandlers.

wxBMPHandler For loading and saving, always installed.
wxPNGHandler For loading (including alpha support) and saving.
wxJPEGHandler For loading and saving.
wxGIFHandler Only for loading, due to legal issues.
wxPCXHandler For loading and saving (see below).
wxPNMHandler For loading and saving (see below).
wxTIFFHandler For loading and saving.
wxIFFHandler For loading only.
wxXPMHandler For loading and saving.
wxICOHandler For loading and saving.
wxCURHandler For loading and saving.
wxANIHandler For loading only.

When saving in PCX format, wxPCXHandler will count the number of different colours in the image; if there are 256 or less colours, it will save as 8 bit, else it will save as 24 bit.

Loading PNMs only works for ASCII or raw RGB images. When saving in PNM format, wxPNMHandler will always save as raw RGB.

Derived from

wxObject

Include files

<wx/image.h>

See also

wxBitmap, wxInitAllImageHandlers

Members

wxImage::wxImage
wxImage::~wxImage
wxImage::AddHandler
wxImage::CleanUpHandlers
wxImage::ComputeHistogram
wxImage::ConvertAlphaToMask
wxImage::ConvertToBitmap
wxImage::ConvertToMono
wxImage::Copy
wxImage::Create
wxImage::Destroy
wxImage::FindFirstUnusedColour
wxImage::FindHandler
wxImage::GetImageExtWildcard
wxImage::GetAlpha
wxImage::GetBlue
wxImage::GetData
wxImage::GetGreen
wxImage::GetImageCount
wxImage::GetHandlers
wxImage::GetHeight
wxImage::GetMaskBlue
wxImage::GetMaskGreen
wxImage::GetMaskRed
wxImage::GetPalette
wxImage::GetRed
wxImage::GetSubImage
wxImage::GetWidth
wxImage::HasAlpha
wxImage::HasMask
wxImage::GetOption
wxImage::GetOptionInt
wxImage::HasOption
wxImage::InitStandardHandlers
wxImage::InsertHandler
wxImage::LoadFile
wxImage::Ok
wxImage::RemoveHandler
wxImage::Mirror
wxImage::Replace
wxImage::Rescale
wxImage::Rotate
wxImage::Rotate90
wxImage::SaveFile
wxImage::Scale
wxImage::SetAlpha
wxImage::SetData
wxImage::SetMask
wxImage::SetMaskColour
wxImage::SetMaskFromImage
wxImage::SetOption
wxImage::SetPalette
wxImage::SetRGB
wxImage::operator =
wxImage::operator ==
wxImage::operator !=

wxImage::wxImage

wxImage()

Default constructor.

wxImage(const wxImage& image)

Copy constructor.

wxImage(const wxBitmap& bitmap)

(Deprecated form, use wxBitmap::ConvertToImage instead.) Constructs an image from a platform-dependent bitmap. This preserves mask information so that bitmaps and images can be converted back and forth without loss in that respect.

wxImage(int width, int height, bool clear=true)

Creates an image with the given width and height. If clear is true, the new image will be initialized to black. Otherwise, the image data will be uninitialized.

wxImage(int width, int height, unsigned char* data, bool static_data=false)

Creates an image from given data with the given width and height. If static_data is true, then wxImage will not delete the actual image data in its destructor, otherwise it will free it by calling free().

wxImage(const wxString& name, long type = wxBITMAP_TYPE_ANY, int index = -1)

wxImage(const wxString& name, const wxString& mimetype, int index = -1)

Loads an image from a file.

wxImage(wxInputStream& stream, long type = wxBITMAP_TYPE_ANY, int index = -1)

wxImage(wxInputStream& stream, const wxString& mimetype, int index = -1)

Loads an image from an input stream.

Parameters

width

height

name

stream

type

mimetype

index

Remarks

Depending on how wxWidgets has been configured, not all formats may be available.

Note: any handler other than BMP must be previously initialized with wxImage::AddHandler or wxInitAllImageHandlers.

Note: you can use GetOptionInt to get the hotspot for loaded cursor file: 

    int hotspot_x = image.GetOptionInt(wxIMAGE_OPTION_CUR_HOTSPOT_X);
    int hotspot_y = image.GetOptionInt(wxIMAGE_OPTION_CUR_HOTSPOT_Y);
See also

wxImage::LoadFile

wxPython note: Constructors supported by wxPython are:

wxPerl note: Constructors supported by wxPerl are:

wxImage::~wxImage

~wxImage()

Destructor.

wxImage::AddHandler

static void AddHandler(wxImageHandler* handler)

Adds a handler to the end of the static list of format handlers.

handler

See also

wxImageHandler

bool CanRead(const wxString& filename)

returns true if the current image handlers can read this file

wxPython note: In wxPython this static method is named wxImage_AddHandler.

wxImage::CleanUpHandlers

static void CleanUpHandlers()

Deletes all image handlers.

This function is called by wxWidgets on exit.

wxImage::ComputeHistogram

unsigned long ComputeHistogram(wxImageHistogram& histogram) const

Computes the histogram of the image. histogram is a reference to wxImageHistogram object. wxImageHistogram is a specialization of wxHashMap "template" and is defined as follows:

class WXDLLEXPORT wxImageHistogramEntry
{
public:
    wxImageHistogramEntry() : index(0), value(0) {}
    unsigned long index;
    unsigned long value;
};

WX_DECLARE_EXPORTED_HASH_MAP(unsigned long, wxImageHistogramEntry,
                             wxIntegerHash, wxIntegerEqual,
                             wxImageHistogram);
Return value

Returns number of colours in the histogram.

wxImage::ConvertAlphaToMask

bool ConvertAlphaToMask(unsigned char threshold = 128)

If the image has alpha channel, this method converts it to mask. All pixels with alpha value less than threshold are replaced with mask colour and the alpha channel is removed. Mask colour is chosen automatically using FindFirstUnusedColour.

If the image image doesn't have alpha channel, ConvertAlphaToMask does nothing.

Return value

false if FindFirstUnusedColour returns false, true otherwise.

wxImage::ConvertToBitmap

wxBitmap ConvertToBitmap() const

Deprecated, use equivalent wxBitmap constructor (which takes wxImage and depth as its arguments) instead.

wxImage::ConvertToMono

wxImage ConvertToMono(unsigned char r, unsigned char g, unsigned char b) const

Returns monochromatic version of the image. The returned image has white colour where the original has (r,g,b) colour and black colour everywhere else.

wxImage::Copy

wxImage Copy() const

Returns an identical copy of the image.

wxImage::Create

bool Create(int width, int height, bool clear=true)

Creates a fresh image. If clear is true, the new image will be initialized to black. Otherwise, the image data will be uninitialized.

Parameters

width

height

Return value

true if the call succeeded, false otherwise.

wxImage::Destroy

bool Destroy()

Destroys the image data.

wxImage::FindFirstUnusedColour

bool FindFirstUnusedColour(unsigned char * r, unsigned char * g, unsigned char * b, unsigned char startR = 1, unsigned char startG = 0, unsigned char startB = 0)

Parameters

r,g,b

startR,startG,startB

Finds the first colour that is never used in the image. The search begins at given initial colour and continues by increasing R, G and B components (in this order) by 1 until an unused colour is found or the colour space exhausted.

Return value

Returns false if there is no unused colour left, true on success.

Notes

Note that this method involves computing the histogram, which is computationally intensive operation.

wxImage::FindHandler

static wxImageHandler* FindHandler(const wxString& name)

Finds the handler with the given name.

static wxImageHandler* FindHandler(const wxString& extension, long imageType)

Finds the handler associated with the given extension and type.

static wxImageHandler* FindHandler(long imageType)

Finds the handler associated with the given image type.

static wxImageHandler* FindHandlerMime(const wxString& mimetype)

Finds the handler associated with the given MIME type.

name

extension

imageType

mimetype

Return value

A pointer to the handler if found, NULL otherwise.

See also

wxImageHandler

wxImage::GetImageExtWildcard

static wxString GetImageExtWildcard()

Iterates all registered wxImageHandler objects, and returns a string containing file extension masks suitable for passing to file open/save dialog boxes.

Return value

The format of the returned string is "(*.ext1;*.ext2)|*.ext1;*.ext2".

It is usually a good idea to prepend a description before passing the result to the dialog.

Example:

    wxFileDialog FileDlg( this, "Choose Image", ::wxGetWorkingDirectory(), "", _("Image Files ") + wxImage::GetImageExtWildcard(), wxOPEN );
See also

wxImageHandler

wxImage::GetAlpha

unsigned char GetAlpha(int x, int y) const

Returns the alpha value for the given pixel. This function may only be called for the images with alpha channel, use HasAlpha to check for this.

The returned value is the opacity of the image, i.e. the value of 0 corresponds to the transparent pixels while the value of 255 -- to the opaque ones.

unsigned char * GetAlpha() const

Returns pointer to the array storing the alpha values for this image. This pointer is NULL for the images without the alpha channel. If the image does have it, this pointer may be used to directly manipulate the alpha values which are stored as the RGB ones.

wxImage::GetBlue

unsigned char GetBlue(int x, int y) const

Returns the blue intensity at the given coordinate.

wxImage::GetData

unsigned char* GetData() const

Returns the image data as an array. This is most often used when doing direct image manipulation. The return value points to an array of characters in RGBRGBRGB... format in the top-to-bottom, left-to-right order, that is the first RGB triplet corresponds to the pixel first pixel of the first row, the second one --- to the second pixel of the first row and so on until the end of the first row, with second row following after it and so on.

You should not delete the returned pointer nor pass it to wxImage::SetData.

wxImage::GetGreen

unsigned char GetGreen(int x, int y) const

Returns the green intensity at the given coordinate.

wxImage::GetImageCount

static int GetImageCount(const wxString& filename, long type = wxBITMAP_TYPE_ANY)

static int GetImageCount(wxInputStream& stream, long type = wxBITMAP_TYPE_ANY)

If the image file contains more than one image and the image handler is capable of retrieving these individually, this function will return the number of available images.

name

stream

type

Return value

Number of available images. For most image handlers, this is 1 (exceptions are TIFF and ICO formats).

wxImage::GetHandlers

static wxList& GetHandlers()

Returns the static list of image format handlers.

See also

wxImageHandler

wxImage::GetHeight

int GetHeight() const

Gets the height of the image in pixels.

wxImage::GetMaskBlue

unsigned char GetMaskBlue() const

Gets the blue value of the mask colour.

wxImage::GetMaskGreen

unsigned char GetMaskGreen() const

Gets the green value of the mask colour.

wxImage::GetMaskRed

unsigned char GetMaskRed() const

Gets the red value of the mask colour.

wxImage::GetPalette

const wxPalette& GetPalette() const

Returns the palette associated with the image. Currently the palette is only used when converting to wxBitmap under Windows.

Eventually wxImage handlers will set the palette if one exists in the image file.

wxImage::GetRed

unsigned char GetRed(int x, int y) const

Returns the red intensity at the given coordinate.

wxImage::GetSubImage

wxImage GetSubImage(const wxRect& rect) const

Returns a sub image of the current one as long as the rect belongs entirely to the image.

wxImage::GetWidth

int GetWidth() const

Gets the width of the image in pixels.

See also

wxImage::GetHeight

wxImage::HasAlpha

bool HasAlpha() const

Returns true if this image has alpha channel, false otherwise.

See also

GetAlpha, SetAlpha

wxImage::HasMask

bool HasMask() const

Returns true if there is a mask active, false otherwise.

wxImage::GetOption

wxString GetOption(const wxString& name) const

Gets a user-defined option. The function is case-insensitive to name.

For example, when saving as a JPEG file, the option quality is used, which is a number between 0 and 100 (0 is terrible, 100 is very good).

See also

wxImage::SetOption, wxImage::GetOptionInt, wxImage::HasOption

wxImage::GetOptionInt

int GetOptionInt(const wxString& name) const

Gets a user-defined option as an integer. The function is case-insensitive to name.

See also

wxImage::SetOption, wxImage::GetOption, wxImage::HasOption

wxImage::HasOption

bool HasOption(const wxString& name) const

Returns true if the given option is present. The function is case-insensitive to name.

See also

wxImage::SetOption, wxImage::GetOption, wxImage::GetOptionInt

wxImage::InitStandardHandlers

static void InitStandardHandlers()

Internal use only. Adds standard image format handlers. It only install BMP for the time being, which is used by wxBitmap.

This function is called by wxWidgets on startup, and shouldn't be called by the user.

See also

wxImageHandler, wxInitAllImageHandlers

wxImage::InsertHandler

static void InsertHandler(wxImageHandler* handler)

Adds a handler at the start of the static list of format handlers.

handler

See also

wxImageHandler

wxImage::LoadFile

bool LoadFile(const wxString& name, long type = wxBITMAP_TYPE_ANY, int index = -1)

bool LoadFile(const wxString& name, const wxString& mimetype, int index = -1)

Loads an image from a file. If no handler type is provided, the library will try to autodetect the format.

bool LoadFile(wxInputStream& stream, long type, int index = -1)

bool LoadFile(wxInputStream& stream, const wxString& mimetype, int index = -1)

Loads an image from an input stream.

Parameters

name

stream

type

mimetype

index

Remarks

Depending on how wxWidgets has been configured, not all formats may be available.

Note: you can use GetOptionInt to get the hotspot for loaded cursor file: 

    int hotspot_x = image.GetOptionInt(wxIMAGE_OPTION_CUR_HOTSPOT_X);
    int hotspot_y = image.GetOptionInt(wxIMAGE_OPTION_CUR_HOTSPOT_Y);
Return value

true if the operation succeeded, false otherwise. If the optional index parameter is out of range, false is returned and a call to wxLogError() takes place.

See also

wxImage::SaveFile

wxPython note: In place of a single overloaded method name, wxPython implements the following methods:

wxPerl note: Methods supported by wxPerl are:

wxImage::Ok

bool Ok() const

Returns true if image data is present.

wxImage::RemoveHandler

static bool RemoveHandler(const wxString& name)

Finds the handler with the given name, and removes it. The handler is not deleted.

name

Return value

true if the handler was found and removed, false otherwise.

See also

wxImageHandler

wxImage::Mirror

wxImage Mirror(bool horizontally = true) const

Returns a mirrored copy of the image. The parameter horizontally indicates the orientation.

wxImage::Replace

void Replace(unsigned char r1, unsigned char g1, unsigned char b1, unsigned char r2, unsigned char g2, unsigned char b2)

Replaces the colour specified by r1,g1,b1 by the colour r2,g2,b2.

wxImage::Rescale

wxImage & Rescale(int width, int height)

Changes the size of the image in-place: after a call to this function, the image will have the given width and height.

Returns the (modified) image itself.

See also

Scale

wxImage::Rotate

wxImage Rotate(double angle, const wxPoint& rotationCentre, bool interpolating = true, wxPoint* offsetAfterRotation = NULL)

Rotates the image about the given point, by angle radians. Passing true to interpolating results in better image quality, but is slower. If the image has a mask, then the mask colour is used for the uncovered pixels in the rotated image background. Else, black (rgb 0, 0, 0) will be used.

Returns the rotated image, leaving this image intact.

wxImage::Rotate90

wxImage Rotate90(bool clockwise = true) const

Returns a copy of the image rotated 90 degrees in the direction indicated by clockwise.

wxImage::SaveFile

bool SaveFile(const wxString& name, int type) const

bool SaveFile(const wxString& name, const wxString& mimetype) const

Saves an image in the named file.

bool SaveFile(const wxString& name) const

Saves an image in the named file. File type is determined from the extension of the file name. Note that this function may fail if the extension is not recognized! You can use one of the forms above to save images to files with non-standard extensions.

bool SaveFile(wxOutputStream& stream, int type) const

bool SaveFile(wxOutputStream& stream, const wxString& mimetype) const

Saves an image in the given stream.

Parameters

name

stream

type

mimetype

Return value

true if the operation succeeded, false otherwise.

Remarks

Depending on how wxWidgets has been configured, not all formats may be available.

Note: you can use GetOptionInt to set the hotspot before saving an image into a cursor file (default hotspot is in the centre of the image): 

    image.SetOption(wxIMAGE_OPTION_CUR_HOTSPOT_X, hotspotX);
    image.SetOption(wxIMAGE_OPTION_CUR_HOTSPOT_Y, hotspotY);
See also

wxImage::LoadFile

wxPython note: In place of a single overloaded method name, wxPython implements the following methods:

wxPerl note: Methods supported by wxPerl are:

wxImage::Scale

wxImage Scale(int width, int height) const

Returns a scaled version of the image. This is also useful for scaling bitmaps in general as the only other way to scale bitmaps is to blit a wxMemoryDC into another wxMemoryDC.

It may be mentioned that the GTK port uses this function internally to scale bitmaps when using mapping modes in wxDC.

Example:

    // get the bitmap from somewhere
    wxBitmap bmp = ...;

    // rescale it to have size of 32*32
    if ( bmp.GetWidth() != 32 || bmp.GetHeight() != 32 )
    {
        wxImage image = bmp.ConvertToImage();
        bmp = wxBitmap(image.Scale(32, 32));

        // another possibility:
        image.Rescale(32, 32);
        bmp = image;
    }
See also

Rescale

wxImage::SetAlpha

void SetAlpha(unsigned char *alpha = NULL)

This function is similar to SetData and has similar restrictions. The pointer passed to it may however be NULL in which case the function will allocate the alpha array internally -- this is useful to add alpha channel data to an image which doesn't have any. If the pointer is not NULL, it must have one byte for each image pixel and be allocated with malloc(). wxImage takes ownership of the pointer and will free it.

void SetAlpha(int x, int y, unsigned char alpha)

Sets the alpha value for the given pixel. This function should only be called if the image has alpha channel data, use HasAlpha to check for this.

wxImage::SetData

void SetData(unsigned char*data)

Sets the image data without performing checks. The data given must have the size (width*height*3) or results will be unexpected. Don't use this method if you aren't sure you know what you are doing.

The data must have been allocated with malloc(), NOT with operator new.

After this call the pointer to the data is owned by the wxImage object, that will be responsible for deleting it. Do not pass to this function a pointer obtained through wxImage::GetData.

wxImage::SetMask

void SetMask(bool hasMask = true)

Specifies whether there is a mask or not. The area of the mask is determined by the current mask colour.

wxImage::SetMaskColour

void SetMaskColour(unsigned char red, unsigned char green, unsigned char blue)

Sets the mask colour for this image (and tells the image to use the mask).

wxImage::SetMaskFromImage

bool SetMaskFromImage(const wxImage& mask, unsigned char mr, unsigned char mg, unsigned char mb)

Parameters

mask

mr,mg,mb

Sets image's mask so that the pixels that have RGB value of mr,mg,mb in mask will be masked in the image. This is done by first finding an unused colour in the image, setting this colour as the mask colour and then using this colour to draw all pixels in the image who corresponding pixel in mask has given RGB value.

Return value

Returns false if mask does not have same dimensions as the image or if there is no unused colour left. Returns true if the mask was successfully applied.

Notes

Note that this method involves computing the histogram, which is computationally intensive operation.

wxImage::SetOption

void SetOption(const wxString& name, const wxString& value)

void SetOption(const wxString& name, int value)

Sets a user-defined option. The function is case-insensitive to name.

For example, when saving as a JPEG file, the option quality is used, which is a number between 0 and 100 (0 is terrible, 100 is very good).

See also

wxImage::GetOption, wxImage::GetOptionInt, wxImage::HasOption

wxImage::SetPalette

void SetPalette(const wxPalette& palette)

Associates a palette with the image. The palette may be used when converting wxImage to wxBitmap (MSW only at present) or in file save operations (none as yet).

wxImage::SetRGB

void SetRGB(int x, int y, unsigned char red, unsigned char green, unsigned char blue)

Sets the pixel at the given coordinate. This routine performs bounds-checks for the coordinate so it can be considered a safe way to manipulate the data, but in some cases this might be too slow so that the data will have to be set directly. In that case you will have to get access to the image data using the GetData method.

wxImage::operator =

wxImage& operator =(const wxImage& image)

Assignment operator. This operator does not copy any data, but instead passes a pointer to the data in image and increments a reference counter. It is a fast operation.

Parameters

image

Return value

Returns 'this' object.

wxImage::operator ==

bool operator ==(const wxImage& image) const

Equality operator. This operator tests whether the internal data pointers are equal (a fast test).

Parameters

image

Return value

Returns true if the images were effectively equal, false otherwise.

wxImage::operator !=

bool operator !=(const wxImage& image) const

Inequality operator. This operator tests whether the internal data pointers are unequal (a fast test).

Parameters

image

Return value

Returns true if the images were unequal, false otherwise.