Am 29.01.2023 um 23:36 schrieb Paul B Mahol:
On 1/29/23, Michael Koch <astroelectro...@t-online.de> wrote:
Am 29.01.2023 um 23:07 schrieb Paul B Mahol:
On 1/29/23, Michael Koch <astroelectro...@t-online.de> wrote:
Am 29.01.2023 um 22:05 schrieb Paul B Mahol:
On 1/29/23, Michael Koch <astroelectro...@t-online.de> wrote:
Am 29.01.2023 um 19:32 schrieb Paul B Mahol:
On 1/29/23, Michael Koch <astroelectro...@t-online.de> wrote:
Hello,
if I understood the documentation correctly, the normalize filter
maps
the darkest input pixel to blackpt and the brightest input pixel to
whitept:
darkest pixel --> blackpt
brightest pixel --> whitept
However I need a slightly different mapping:
A black input pixel shall remain black, and the brightest input
pixel
shall become white.
black --> blackpt
brightest pixel --> whitept
With other words: Just multiply all pixels by a suitable constant.
Don't
add or subtract anything.
Is this possible?
Known workaround: Make sure that the input frame contains a black
pixel,
by inserting one in a corner.
Try attached patch.
How must I set the options for the desired behaviour?
Set first strength to reverse of second strength.
So 1.0 and 0.0 or 0.0 and 1.0
I did try with strength=0:strength2=1 but the output isn't as expected.
I'm using this input image:
http://www.astro-electronic.de/flat.png
The pixel values are about 171 in the center and 107 in the top right
corner.
The center to corner ratio is 171 / 107 = 1.6
In the output image I measure 248 in the center (which is almost as
expected, probably correct because I'm measuring the average of a 7x7
neighborhood), but I measure 122 in the top right corner.
The center to corner ratio is 248 / 122 = 2.03
The corner is too dark.
I checked with oscilloscope filter (s=1:tw=1:t=1:x=0), far left pixels
(as they are darkest) and they are not changing (min values are same
with and without filter run)
With default parameters and just strength(2) set to your values, so
the darkest pixels are left untouched. Did not checked brightest
pixels output, but they should be correct too.
But that's not the behaviour I need. All pixels shall be multiplied by
the same suitable constant, so that the brightest pixel becomes white.
Input center: 171
Input corner: 107
constant c = 255 / 171 =1.49
Output center: 171 * c = 255
Output corner: 107 * c = 160
Normalization does not do that and that functionality does not belong
to such filter, it stretches ranges of all pixel values so they reach
maximal possible range.
Can't you just add an option that disables the minimum finding
algorithm, and set the minimum to zero (=black)? That would do the job.
Let me explain why I need this kind of normalization.
Most lenses have vignetting. Especially in astronomical images,
vignetting must be corrected before any other image processing can be
done. For this purpose a flatfield image is taken with the same lens at
the same aperture, but with a uniform white screen in front of the lens.
Normally the flatfield image is exposed at roughly 50% gray level, to
avoid problems with nonlinearity near white level. The linked image is
the flatfield.
Vignetting in an astronomical image is corrected by dividing the image
by the flatfield. That can be done with the blend filter.
If I use the flatfied as-is (with roughly 50% gray level), then the
image is effectively multiplied by a factor 2. That's a problem because
bright pixels might get clipped. To minimize this problem, I want to
normalize the flatfield as close to white level as possible, before
using it.
Michael
_______________________________________________
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-user
To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
