Averaging them does tent to blr the result. I did that with my old camera. This
one has it's own sensor, which is good. However, the last few images at dusk
are pretty pror quality. I tried to count the number of discrete colours in the
image
NumColours=`identify -verbose /var/www/html/weather/images/current.jpg | grep
Colors: | awk '{print $2}'`
but it's not really any use. Identify does give you a min/max/ave/std dev on
each channel, which may help?
Steve
On Tue, 10 Oct 2006 19:57:16 +1300
Craig FALCONER <[EMAIL PROTECTED]> wrote:
> Just keep the last 10 images or something... Not really a big deal.
>
> -----Original Message-----
> From: Andrew Errington [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, 10 October 2006 2:51 p.m.
> To: [email protected]
> Subject: OT: Light-level in an image
>
>
> Hi,
>
> Can anyone comment knowledgably on determining the light level in a JPG
> image snapped by a webcam?
>
> I have the simple requirement of taking hourly snapshots from my webcam in
> the back garden and posting them on my webpage. At the moment I have a
> cron job, which I tweak during the year to adjust when it takes a picture
> (i.e from 8 to 5 in winter to 5 till 10 in summer), but really it should be
> automated. I could rig up a light sensor, and the PC could query it before
> taking a webcam image, but really, the webcam itself is a light sensor
> (duh!).
>
> I am thinking of the imagemagick 'identify' command, and maybe extracting
> the mean value of the red, green and blue channels and comparing them to a
> hard limit. Does this idea have merit, or is there a better tool?
>
> I could also just look at the file size: at night the images are mostly
> black, which compresses to a very small file size.
>
> Comments are welcome,
>
> Thanks,
>
> Andrew
>
>
