this week I'll show you four ways to get rid of long exposure noise generally
there are two different types of noise there's high ISO noise and long exposure
noise in today's tutorial we're talking about long exposure noise if you want to
learn about high ISO noise click on the I in the corner or the link in the
description long exposure noise is very different to high ISO noise it's
basically lots of hot pixels all over your shot and they tend to be brighter
in the shadows they're normally made up of red green or blue pixels and they
really stand out especially when you try and bring the shadows back when you
leave your camera on and take a number of shots they'll normally be in exactly
the same place throughout those shots every now and then depending on what
camera brand you have the camera will remap the sensor so basically the
pattern of these hot pixels will change over time also if you click on sensor
clean in your camera I think then it also remaps the sensor so you'll get a
different pattern of hot pixels this isn't so important for certain
techniques but when you're taking a dark frame it just means that you'll need to
take your dark frame at the same time as you took the photographs but more about
that later so these are the ways to get rid of long exposure noise there's an
option in most cameras nowadays called long exposure noise reduction and this
basically gets rid of these little hot pixels however if you're under a time
constraint or you're shooting a time-lapse or ding star trails this
really isn't an option when you take a photograph with this setting switched on
you'll have to wait exactly the same time as the length of exposure that you
took so if you've taken a 1 minute exposure you'll have to wait another
minute before using the camera and this is completely locked down the camera
won't let you do anything at all it'll sit there with processing image on
the monitor now on this first shot I went down to the marina and I took a
long exposure shot so this one was about 4 minutes
I put the long exposure noise reduction on so I had to wait another four minutes
for the shot to be processed if I look at the shot where I don't have long
exposure noise reduction switched on you can see all of these hot pixels in the
shadows and then we go back to the one where long exposure noise reduction was
switched on in the camera you can see all of these hot pixels have gone so you
can see when you have long exposure noise reduction turned on the camera
does a really good job dark frames are really well known in Astro photography
but if you've come from the photography side of things you may not know what
they are it's basically a way of getting a readout from the sensor with just
these hot pixels on it's really simple but you have to do it at the location
where you've taken the photographs for best results what you basically do to
get a dark frame is put the lens cap back on your camera and take another
photograph with exactly the same settings for this example I've only
taken one dark frame but let's say if you are stacking a lot of
astrophotography shots you may want to take a series of dark frames as well
then a program like starry landscape tracker would then use all of these dark
frames and then work out what exactly are hot pixels and what are stars this
is the process of stacking in Astro photography and I'm going to cover this
in a future episode so by taking a dark frame you're separating out water hot
pixels and what are pixels that make up your photograph once again for dark
frames I've taken a shot down the marina I have this shot which I took over four
minutes this was the one where there's noise in that corner and noise pretty
much all over the frame after this shot I took another photo with the lens cap
on and this is my dark frame all the
settings are exactly the same just with no light getting into the camera so to
make these hot pixels stand out I've bumped up my exposure and I've opened up
my shadows what I'm gonna have to do before I take them across to photoshop
is drop these levels back down so go on this one I'm gonna drop the exposure
lights and the shadows back to zero and the same with a dark frame can see all
those hot pixels but again I'm gonna take them all back to zero now what I'll
do is I'll select my photograph and the dark frame and then edit in openers
layers in Photoshop once it's brought them across into
Photoshop make sure your dark frame is on the top and then on this blend mode
click on subtract and then save your image once it's saved go back into
Lightroom and then it'll open this new image as a tiff file so this is the
blended file and this is the original again if we look down in that bottom
corner what I'm going to do is bump up the exposure and the shadows so we can
really see into those shadows and see what's there select the other one that's
sick now if we switch over to the TIFF you can see not all but most of this
long exposure noise has gone so this was before the dark frame this is after the
dark frame there are still a few of these hot pixels but nowhere near as
many as there were to start with so as you can see getting a dark frame in the
field is really worth it it's a very quick and easy process to get rid of
these hot pixels in Photoshop this is the most tedious way of getting rid of
these hot pixels but sometimes it can be the most effective so for manual removal
I've got this image here I did some short star trails above my car you can
already see by the name of this image that I've edited it a couple of times I
blended the image to get the star trails I think I've blended about 400 images so
I've zoomed in on this area where these hot pixels are being quite stubborn so
I'm gonna zoom in probably four to one and you can really see those hot pixels
there so to manually remove them go to this tool here which is the spot removal
to you want to make it as small as the
pixels pretty much then literally just click on these pixels this is a bit of a
tedious task but if you want the best-looking image possible this is what
it takes if the hot pixel falls on a line of a darker and a lighter area just
watch where it samples the image from as you can see here it's sampled a similar
part of the dune as I said this takes a long time to do so all you want to do is
be patient have a cup of tea or coffee or a beer and then just plunge your way
through it if you use this in conjunction with the next technique that
we're going to use all the dark frames it'll really speed up the process and
you'll only have a few of these hot pixels to remove if you don't have the
patience to manually remove them you've forgotten to take a dark frame and you
didn't have long exposure noise reduction on then this is another way to
do it so this is the image that I've got and you can see there's quite a bit of
this long exposure noise in the shadows so what I'm gonna do is right click on
the image edit in Adobe Photoshop I'm going to edit the copy with Lightroom
adjustments so this is a fairly straightforward way of doing things
probably want to do let's click on filter noise dust and scratches you get
your radius to two and then play around with the threshold with this little
preview box if you actually click and hold on it it'll show you what the image
was like and then when you let go it'll show you what the image will be like
once you put this filter on so you can see it's getting rid of a lot of that
noise in the shadows all we want to do is make sure it's not getting rid of too
many of the stars and it really is so I'll bring that threshold down now if
I okay on that you can see this really affects the Stars so if you're doing
Astro shots you've really got to watch what you're doing with this filter and
this is why taking a dark frame at night is really important it's so that the
computer can distinguish between these hot pixels and the stars when the a7 r2
came out there was a firmware that came out that ended up being nicknamed the
star eater and I think this is what it was doing in camera so the way to get
around this is to split up the ground from the sky and they not can just edit
the ground without affecting the stars in the sky
first of all I'll unlock this layer and then I'll duplicate the layer so right
click duplicate layer ok then click on this little box here what I'm doing here
is a bit more technical but if you don't have any stars in your shot you can just
use the dust and scratches filter with this more advanced technique it means
that I'm protecting my stars and getting rid of all of these hot pixels in the
land the foreground and anywhere where there aren't any stars so this is known
as a mask what this does is anything that's white it will show anything
that's black will not show you so in this mask I'm going to create a gradient
I'm going to make sure it's selected from black to white I'm going to hold
down alt or option and click on the mask and this brings up the mask
so I've just got a line up the mask with the ground that's about right
so now with this top layer with this mask all of this white area will be
affected by anything that I do to this top layer and then nothing can be seen
on this black area above so I'll click back on the layer I'll click on filter
noise dust and scratches again you can see when I click and hold I can see the
noise when I let go it's not but it's not affecting the stars anymore so I'll
click on OK now when i zoom in on the ground I've
made that top layer invisible and you can still see all of this noise around
here when I click back on it the majority of that noise is gone once it's
saved go back into Lightroom and then ill open this new image has a tiff file
so you can see with the original image we've still got this long exposure noise
on it and you can see that clearly zoomed in on a one-to-one scale if we go
to the one where I used the dust and scratches filter it's a lot cleaner and
when i zoom out even at this scale you can see it is a lot cleaner now because
I used the mask to block out the sky the stars haven't been affected the problem
with a dust and scratches filter is it can very quickly degrade your image and
make it look a little bit strange so what I try and do is get it just on the
boundary of getting rid of most of the hot pixels and then I'll manually remove
the rest of them and that's about it this long exposure noise can be really
annoying and if you don't know how to get rid of it it can ruin your
photograph however by using at least one of these techniques you can pretty much
get rid of all of that long exposure noise as always if you like what you see
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