Image Data

Image data in a pixbuf is stored in memory in uncompressed, packed format. Rows in the image are stored top to bottom, and in each row pixels are stored from left to right. There may be padding at the end of a row. The "rowstride" value of a pixbuf, as returned by gdk_pixbuf_get_rowstride(), indicates the number of bytes between rows.

put_pixel() Example

The following code illustrates a simple put_pixel() function for RGB pixbufs with 8 bits per channel with an alpha channel. It is not included in the gdk-pixbuf library for performance reasons; rather than making several function calls for each pixel, your own code can take shortcuts.

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static void
put_pixel (GdkPixbuf *pixbuf, int x, int y, guchar red, guchar green, guchar blue, guchar alpha)
{
  int width, height, rowstride, n_channels;
  guchar *pixels, *p;

  n_channels = gdk_pixbuf_get_n_channels (pixbuf);

  g_assert (gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB);
  g_assert (gdk_pixbuf_get_bits_per_sample (pixbuf) == 8);
  g_assert (gdk_pixbuf_get_has_alpha (pixbuf));
  g_assert (n_channels == 4);

  width = gdk_pixbuf_get_width (pixbuf);
  height = gdk_pixbuf_get_height (pixbuf);

  g_assert (x >= 0 && x < width);
  g_assert (y >= 0 && y < height);

  rowstride = gdk_pixbuf_get_rowstride (pixbuf);
  pixels = gdk_pixbuf_get_pixels (pixbuf);

  p = pixels + y * rowstride + x * n_channels;
  p[0] = red;
  p[1] = green;
  p[2] = blue;
  p[3] = alpha;
}

This function will not work for pixbufs with images that are other than 8 bits per sample or channel, but it will work for most of the pixbufs that GTK+ uses.

If you are doing memcpy() of raw pixbuf data, note that the last row in the pixbuf may not be as wide as the full rowstride, but rather just as wide as the pixel data needs to be. That is, it is unsafe to do memcpy (dest, pixels, rowstride * height) to copy a whole pixbuf. Use gdk_pixbuf_copy() instead, or compute the width in bytes of the last row as width * ((n_channels * bits_per_sample + 7) / 8).

gdk_pixbuf_get_colorspace ()

GdkColorspace
gdk_pixbuf_get_colorspace (const GdkPixbuf *pixbuf);

Queries the color space of a pixbuf.

gdk_pixbuf_get_n_channels ()

int
gdk_pixbuf_get_n_channels (const GdkPixbuf *pixbuf);

Queries the number of channels of a pixbuf.

gdk_pixbuf_get_has_alpha ()

gboolean
gdk_pixbuf_get_has_alpha (const GdkPixbuf *pixbuf);

Queries whether a pixbuf has an alpha channel (opacity information).

gdk_pixbuf_get_bits_per_sample ()

int
gdk_pixbuf_get_bits_per_sample (const GdkPixbuf *pixbuf);

Queries the number of bits per color sample in a pixbuf.

gdk_pixbuf_get_pixels ()

guchar *
gdk_pixbuf_get_pixels (const GdkPixbuf *pixbuf);

Queries a pointer to the pixel data of a pixbuf.

gdk_pixbuf_get_pixels_with_length ()

guchar *
gdk_pixbuf_get_pixels_with_length (const GdkPixbuf *pixbuf,
                                   guint *length);

Queries a pointer to the pixel data of a pixbuf.

[rename-to gdk_pixbuf_get_pixels]

Since: 2.26

gdk_pixbuf_get_width ()

int
gdk_pixbuf_get_width (const GdkPixbuf *pixbuf);

Queries the width of a pixbuf.

gdk_pixbuf_get_height ()

int
gdk_pixbuf_get_height (const GdkPixbuf *pixbuf);

Queries the height of a pixbuf.

gdk_pixbuf_get_rowstride ()

int
gdk_pixbuf_get_rowstride (const GdkPixbuf *pixbuf);

Queries the rowstride of a pixbuf, which is the number of bytes between the start of a row and the start of the next row.

gdk_pixbuf_get_byte_length ()

gsize
gdk_pixbuf_get_byte_length (const GdkPixbuf *pixbuf);

Returns the length of the pixel data, in bytes.

Since: 2.26

gdk_pixbuf_get_option ()

const gchar *
gdk_pixbuf_get_option (GdkPixbuf *pixbuf,
                       const gchar *key);

Looks up key in the list of options that may have been attached to the pixbuf when it was loaded, or that may have been attached by another function using gdk_pixbuf_set_option().

For instance, the ANI loader provides "Title" and "Artist" options. The ICO, XBM, and XPM loaders provide "x_hot" and "y_hot" hot-spot options for cursor definitions. The PNG loader provides the tEXt ancillary chunk key/value pairs as options. Since 2.12, the TIFF and JPEG loaders return an "orientation" option string that corresponds to the embedded TIFF/Exif orientation tag (if present). Since 2.32, the TIFF loader sets the "multipage" option string to "yes" when a multi-page TIFF is loaded. Since 2.32 the JPEG and PNG loaders set "x-dpi" and "y-dpi" if the file contains image density information in dots per inch.

gdk_pixbuf_set_option ()

gboolean
gdk_pixbuf_set_option (GdkPixbuf *pixbuf,
                       const gchar *key,
                       const gchar *value);

Attaches a key/value pair as an option to a GdkPixbuf. If key already exists in the list of options attached to pixbuf , the new value is ignored and FALSE is returned.

Since: 2.2

gdk_pixbuf_remove_option ()

gboolean
gdk_pixbuf_remove_option (GdkPixbuf *pixbuf,
                          const gchar *key);

Remove the key/value pair option attached to a GdkPixbuf.

Since: 2.36

gdk_pixbuf_get_options ()

GHashTable *
gdk_pixbuf_get_options (GdkPixbuf *pixbuf);

Returns a GHashTable with a list of all the options that may have been attached to the pixbuf when it was loaded, or that may have been attached by another function using gdk_pixbuf_set_option().

See gdk_pixbuf_get_option() for more details.

Since: 2.32

gdk_pixbuf_copy_options ()

gboolean
gdk_pixbuf_copy_options (GdkPixbuf *src_pixbuf,
                         GdkPixbuf *dest_pixbuf);

Copy the key/value pair options attached to a GdkPixbuf to another. This is useful to keep original metadata after having manipulated a file. However be careful to remove metadata which you've already applied, such as the "orientation" option after rotating the image.

Since: 2.36

gdk_pixbuf_read_pixels ()

const guint8 *
gdk_pixbuf_read_pixels (const GdkPixbuf *pixbuf);

Returns a read-only pointer to the raw pixel data; must not be modified. This function allows skipping the implicit copy that must be made if gdk_pixbuf_get_pixels() is called on a read-only pixbuf.

Since: 2.32

enum GdkPixbufError

An error code in the GDK_PIXBUF_ERROR domain. Many gdk-pixbuf operations can cause errors in this domain, or in the G_FILE_ERROR domain.

GDK_PIXBUF_ERROR

#define GDK_PIXBUF_ERROR gdk_pixbuf_error_quark ()

Error domain used for pixbuf operations. Indicates that the error code will be in the GdkPixbufError enumeration. See GError for information on error domains and error codes.

enum GdkColorspace

This enumeration defines the color spaces that are supported by the gdk-pixbuf library. Currently only RGB is supported.

enum GdkPixbufAlphaMode

These values can be passed to gdk_pixbuf_xlib_render_to_drawable_alpha() to control how the alpha channel of an image should be handled. This function can create a bilevel clipping mask (black and white) and use it while painting the image. In the future, when the X Window System gets an alpha channel extension, it will be possible to do full alpha compositing onto arbitrary drawables. For now both cases fall back to a bilevel clipping mask.

GdkPixbuf

typedef struct _GdkPixbuf GdkPixbuf;

This is the main structure in the gdk-pixbuf library. It is used to represent images. It contains information about the image's pixel data, its color space, bits per sample, width and height, and the rowstride (the number of bytes between the start of one row and the start of the next).

The “bits-per-sample” property

  “bits-per-sample”          gint

The number of bits per sample. Currently only 8 bit per sample are supported.

Flags: Read / Write / Construct Only

Allowed values: [1,16]

Default value: 8

The “colorspace” property

  “colorspace”               GdkColorspace

The colorspace in which the samples are interpreted.

Flags: Read / Write / Construct Only

Default value: GDK_COLORSPACE_RGB

The “has-alpha” property

  “has-alpha”                gboolean

Whether the pixbuf has an alpha channel.

Flags: Read / Write / Construct Only

Default value: FALSE

The “height” property

  “height”                   gint

The number of rows of the pixbuf.

Flags: Read / Write / Construct Only

Allowed values: >= 1

Default value: 1

The “n-channels” property

  “n-channels”               gint

The number of samples per pixel. Currently, only 3 or 4 samples per pixel are supported.

Flags: Read / Write / Construct Only

Allowed values: >= 0

Default value: 3

The “pixel-bytes” property

  “pixel-bytes”              GBytes *

Readonly pixel data.

Flags: Read / Write / Construct Only

The “pixels” property

  “pixels”                   gpointer

A pointer to the pixel data of the pixbuf.

Flags: Read / Write / Construct Only

The “rowstride” property

  “rowstride”                gint

The number of bytes between the start of a row and the start of the next row. This number must (obviously) be at least as large as the width of the pixbuf.

Flags: Read / Write / Construct Only

Allowed values: >= 1

Default value: 1

The “width” property

  “width”                    gint

The number of columns of the pixbuf.

Flags: Read / Write / Construct Only

Allowed values: >= 1

Default value: 1