Re: Image manipulation and Scaling

[Dov Grobgeld <dov grobgeld gmail com>]

The following code does it:

// your original data assumed to be in a continous structure of gray.
// Preferably in a structure.
float *src_buf;
int img_width = 256;
int img_height = 256;

// You destination
GdkPixbuf *dst = gdk_pixbuf_new(...);
guint8 *dst_buf = gdk_pixbuf_get_data();
guint src_stride = gdk_pixbuf_get_row_stride(dst);

// Find min and max unless you have user min and user max
float min = HUGE;
float max = -HUGE;
for (int i=0; i<img_width*img_height; i++) {
    float gl = src_buf[i];
    if (gl < min)
        min = gl;
    else if (gl > max)
        max = gl;
}

// Rescale
for (int row_idx=0; row_idx<img_height; row_idx++) {
    guint *dst_row = src_buf + row_stride;
    for (int col_idx=0; col_idx<img_height; col_idx++) {
        float src_gl = src_buf[row_idx*img_width + col_idx];
        float dst_gl = (src_gl - min) / (max-min) * 255;
        // clip
        if (dst_gl < 0)
            dst_gl = 0;
        else if (dst_gl > 255)
            dst_gl = 255;
        // Assign to rgb
        for (int i=0; i<3; i++) {
            dst_row[col_idx*3+i] = dst_gl;
    }
}

Changing to support user min and max and source RGB image is left as an
exercise to the reader.

And regarding whether you can support zoom without GtkImageView or
GtkImageViewer, obviously yes since these are written based on lower level
gtk structures. The trivial (and memory wasteful way) is to rescale the
image based on zoom level and show it in a view port.

Regards,
Dov

Wed, Feb 3, 2010 at 08:41, Gorav <gorav s mst-india com> wrote:
On Wed, Feb 3, 2010 at 08:41, Gorav <gorav s mst-india com> wrote:

Thanks for reply.
> Can you please elaborate more on Converting More than 8bit image to 8 bit
> image.
>
> And, apart from GtkImageView, is there no other way of image scaling?
>
>
> Thanks
> Gorav
>
>
> On 02/03/2010 12:02 PM, Dov Grobgeld wrote:
>
> > Even if your image has more than eight bits you can always convert it to
> > 8-bit according to a user setting defining the grey level max and min to
> > be
> > used for the convertion (known as window and level in the medical image
> > community). That's exactly how I do it in my image viewer giv. The image
> > is
> > held in a GivImage that is overloaded for various bit integer or floating
> > widths and is then converted according to the user level setting before
> > being displayed.
> >
> > Btw, if you would like to have interactive zooming of the image being
> > displayed you may want to consider using my GtkImageViewer instead of
> > GtkImage. (There is also the GtkImageView by Björn Lindquist with similar
> > and different functionality.)
> >
> > See: http://giv.sourceforge.net/gtk-image-viewer/
> >
> > Regards,
> > Dov
> >
> > On Wed, Feb 3, 2010 at 04:19, Lars Wirzenius<liw liw fi>  wrote:
> >
> >
> >
> > > On Tue, 2010-02-02 at 17:25 +0530, Gorav wrote:
> > >
> > >
> > > > Hi
> > > >
> > > >
> > > > I need to do some image manipulation using GTK, and I want to view some
> > > > proprietary image formats. So, I can prepare RGB data. But, which widget
> > > > and API to be use to draw pixels on screen.
> > > >
> > > >
> > > > I used GtkImage using Pixbuf, but it supports only 8 bits per sample.
> > > Have you looked at GdkPixbuf for holding the image data? You may need to
> > > write converter plugins to load and store images from files for your
> > > proprietary formats, but after that, all the in-memory stuff should work
> > > fine.
> > >
> > >
> > > _______________________________________________
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> > > http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
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