J
Joel Hedlund
Hi!
I'm developing a pygtk application where I need to show images zoomed in
so that the user can see individual pixels. gtk.gdk.Pixbuf.scale()
seemed ideal for this, but if I set offset_x and offset_y to anything
other than 0, the resulting image is heavily distorted and the offset is
wrong. I've searched the internet for any snippet of code that uses this
function with nonzero offset, but even after several hours of searching
I've still come up blank. I think this may be a bug, but since it seems
so fundamental I think it's way more likely that I've misunderstood
something, so I thought I'd pass this by c.l.p first. Any help is
greatly appreciated.
I wrote a test program to show off this behavior. Please find attached
an image of David Hasselhoff with some puppies to help facilitate this
demonstration. (feel free to use any image, but who doesn't like
Hasselhoff and puppies?)
show_hasselhoff.py
#-------------------------------------------------------
import gtk
original = gtk.gdk.pixbuf_new_from_file('hasselhoff.jpeg')
w = original.get_width()
h = original.get_height()
interp = gtk.gdk.INTERP_NEAREST
nice = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, w, h)
ugly = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, w, h)
original.scale(nice, 0, 0, w, h, 0, 0, 2, 2, interp)
original.scale(ugly, 0, 0, w, h, w/2, h/2, 2, 2, interp)
outtake = original.subpixbuf(w/4, h/4, w/2, w/2)
expected = outtake.scale_simple(w, h, interp)
w = gtk.Window()
hbox = gtk.HBox()
hbox.add(gtk.image_new_from_pixbuf(original))
hbox.add(gtk.image_new_from_pixbuf(nice))
hbox.add(gtk.image_new_from_pixbuf(ugly))
hbox.add(gtk.image_new_from_pixbuf(expected))
w.add(hbox)
w.show_all()
w.connect('destroy', gtk.main_quit)
gtk.main()
#-------------------------------------------------------
When you run this, you should see 4 images in a window. From left to
right: original, nice, ugly and expected. nice, ugly and expected are
scaled/cropped copies of original, but ugly and expected are offset to
show less mullet and more face. expected is what I expected ugly to turn
out like judging from the pygtk docs.
Things to note about ugly:
* The topleft pixel of original has been stretched to the area of
offset_x * offset_y.
* The first offset_x - 1 top pixels of original have been scaled by a
factor 2 horizontally and then stretched vertically to the height of
offset_y.
* Vice versa for the first offset_y - 1 leftmost pixels of original.
* The remaining area of ugly is a scaled version of
original(1,1,width/2-1,height/2-1).
Things to note about the methods:
* This behavior is constant for all interpolation methods.
* This behavior is identical in gtk.gdk.Pixbuf.compose().
This can't possibly be how this is supposed to work! Have I
misunderstood something, or is this a bug?
Cheers!
/Joel Hedlund
I'm developing a pygtk application where I need to show images zoomed in
so that the user can see individual pixels. gtk.gdk.Pixbuf.scale()
seemed ideal for this, but if I set offset_x and offset_y to anything
other than 0, the resulting image is heavily distorted and the offset is
wrong. I've searched the internet for any snippet of code that uses this
function with nonzero offset, but even after several hours of searching
I've still come up blank. I think this may be a bug, but since it seems
so fundamental I think it's way more likely that I've misunderstood
something, so I thought I'd pass this by c.l.p first. Any help is
greatly appreciated.
I wrote a test program to show off this behavior. Please find attached
an image of David Hasselhoff with some puppies to help facilitate this
demonstration. (feel free to use any image, but who doesn't like
Hasselhoff and puppies?)
show_hasselhoff.py
#-------------------------------------------------------
import gtk
original = gtk.gdk.pixbuf_new_from_file('hasselhoff.jpeg')
w = original.get_width()
h = original.get_height()
interp = gtk.gdk.INTERP_NEAREST
nice = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, w, h)
ugly = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, w, h)
original.scale(nice, 0, 0, w, h, 0, 0, 2, 2, interp)
original.scale(ugly, 0, 0, w, h, w/2, h/2, 2, 2, interp)
outtake = original.subpixbuf(w/4, h/4, w/2, w/2)
expected = outtake.scale_simple(w, h, interp)
w = gtk.Window()
hbox = gtk.HBox()
hbox.add(gtk.image_new_from_pixbuf(original))
hbox.add(gtk.image_new_from_pixbuf(nice))
hbox.add(gtk.image_new_from_pixbuf(ugly))
hbox.add(gtk.image_new_from_pixbuf(expected))
w.add(hbox)
w.show_all()
w.connect('destroy', gtk.main_quit)
gtk.main()
#-------------------------------------------------------
When you run this, you should see 4 images in a window. From left to
right: original, nice, ugly and expected. nice, ugly and expected are
scaled/cropped copies of original, but ugly and expected are offset to
show less mullet and more face. expected is what I expected ugly to turn
out like judging from the pygtk docs.
Things to note about ugly:
* The topleft pixel of original has been stretched to the area of
offset_x * offset_y.
* The first offset_x - 1 top pixels of original have been scaled by a
factor 2 horizontally and then stretched vertically to the height of
offset_y.
* Vice versa for the first offset_y - 1 leftmost pixels of original.
* The remaining area of ugly is a scaled version of
original(1,1,width/2-1,height/2-1).
Things to note about the methods:
* This behavior is constant for all interpolation methods.
* This behavior is identical in gtk.gdk.Pixbuf.compose().
This can't possibly be how this is supposed to work! Have I
misunderstood something, or is this a bug?
Cheers!
/Joel Hedlund