Re: Acquring RGB values from GdkPixbuf

[Christopher Anderson <sidewinder asu gmail com>]

Are you displaying the captured pixbuf to the screen so you can see
what it looks like? If so, does it look as you would expect?

Chris Anderson


On 6/15/05, Michal Porzuczek <mporzuczek gmail com> wrote:
> Hi,
> 
> I am getting RGB videofeed from a camera and I am storing it in a
> PixBuf, from this PixBuf I wish to be able to acquire the shade
> (grayscale) value of pixels located at a particular x and y location.
> 
> I have looked at the put_pixel() example in the API reference
> http://www.gtk.org/api/2.6/gdk-pixbuf/gdk-pixbuf-gdk-pixbuf.html
> I acquired the red/green/blue values from the p[0]..p[2] values and
> then I performed the following transformation that should give me a
> grayscale image 0.299*Red+0.587*Green+0.114*Blue.
> 
> I then attempted to test out how it would acquire pixel values so what
> I did was I took a white sheet of paper and drew thick black lines to
> see if they can be detected amongst the white paper. When I checked
> the values I noticed that there was almost no difference between the
> pixels that were white and black. On the other hand if I covered up
> the whole viewport of the camera I would get very low values and if I
> put a light source right up to it I would get really high values. I am
> wondering why it isn't detecting the dark lines on a sheet of paper
> but it does detect it if I cover the whole camera so it's dark or make
> it very bright.
> 
> I was wondering if may be due to the fact that the example is for RGBA
> images and not RGB and the calculations for Pixel would be different
> for RGB images although this dosen't necessarily make sense to me
> since it assumes they are 8 bit images.
> 
> Thanks for the help,
> 
> Michal
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