From time to time I notice on the chats that people have some
problems with their (digital) photos. Underexposure, noise, lack of detail
and/or color, etc. Sometimes I see attempts of improving the result with
the aid of rather destructive filters such as Brightness. I have edited
thousands of photos professionally, and I like to share a few basic techniques
here which you can use to enhance your own photos right away.
Instead of diving in too deep (there are tons of extensive
books on this topic, so if you like to dive in deeper, buy a 500 page
book!), consider these techniques as a starting point for your own explorations.
This also means that sometimes I chose to compromise functionality for
simplicity. I fully recommend you buy an advanced book for the program
of your choice if you want to take things further. As I will never be
able to hand you the techniques on a single page on the web, and with
the time I was able to put in!
This article is solely about the editing of photos, and not
about tips & tricks of shooting aurora in the field. There are quite
a lot of tutorials and articles to be found on the web in that area. See
the FAQ for a few suggestions.
Links to some of the programs used in this article: Paint Shop Pro, Gimp (Windows download) and the Gimp plugin Registry.
My thanks go to the next people who helped me create this
article: Annemarie,
Cheryl, Arno
Paanstra, Bud Kuenzli
and Johan op den Dries for letting
me make use of their photos. And to Bud Kuenzli, Robert B Slobins, Peter
Sproule and Beliboko
for proof reading the article (Beliboko in special, thanks both for your
thoughts on the described techniques!) .
This page is also available in Dutch.
Quick links:
1. General Tips
2. Removing 'Hot Pixels'
3. Removing Noise
4. Underexposed Photos
5. Detail Enhancement
6. Enhancing Colors
7. Sharpening Images
1. General tips
- Once you opened a photo, immediately duplicate that image,
and close the original. This way you will not accidentally overwrite
your original.
- I always prefer to work using a layer with a copy of
the photo I am working on. This way I can quickly switch the layer
on and off to see the changes. This just works easier for me then using
un- and redo.
- Sometimes, some effects can be a bit too much, and then
you were looking for a mix between the original, and the edited version.
In that case, I like to place the edited version on top of the original
image as a new layer, and then play with the transparency until I get
the desired effect.
- If you need to do several steps to edit your photo,
start with the big steps first, and work up to the subtle effects in the
end. A logical order would be for example: remove noise, sharpen the image,
enhance details and finally make subtle adjustments to the color. Ofcourse,
you don't always need all these steps.
- Consider using the RAW storage function if your camera
supports that. Using this mode it will store the image it captured
without any processing and JPeg compression. This will allow more freedom
for you to change things like exposure, color adjustments, etc. Often
camera's offering this mode come with software written for such tasks.
There is a downside too, RAW takes a lot more storage space,
so bring enough storage media! Also, it will take a bit longer before
the images are being written to your storage medium. That can be awkward
when you have a full buffer, the camera is still writing, and that arc
is just making the most beautiful curve ...
- It is really easy to 'over do' an effect. Especially
on things like color adjustments when you see a certain effect is working,
it is really easy to over do it. Once done, save the image, and maybe
have a fresh look at it the next day, and see whether you still like the
image.
This is also true for example with noise removal. All photos
carry some amount of noise, and it makes them look natural. Remove too
much, and your image will look oddly smeared out.
- All the techniques explained here affect the entire photo.
Often you only want to have the effect applied to a certain area.
All good paint programs come with selection tools to allow you to do so.
I did not want to make this page too complex, and usually each program
has their own specific way to work with selections, making things even
more complicated for first time users. A tip: often I like to apply the
effect on a layer with a copy of the photo, and then use the eraser with
varying widths, edges and transparencies to remove the unwanted areas.
- Crap in, crap out. Naturally, we like
to have a correctly shot photo to begin with. But if your camera does
not have the needed functionality or you simply used the wrong settings,
or you have an otherwise nice photo which was simply underexposed a bit,
then there are ways to enhance it. Do not expect miracles however, if
the source material is of too low quality, you will never win a price
with it! The FAQ has a few links to articles on
the Net that can help you with the correct settings etc. in the field.
Back to the menu.
2. Removing 'Hot Pixels'
The surface of a CCD inside a digital camera consists of thousand
of pixels, each sensitive to light and building up the final image. Sometimes,
one or more of those pixels can become defective, which results in a so-called
'hot pixel'. They show up as a bright red, green or blue pixel in our
photo. In the case of aurora and astronomy photography this defect is
quite easy to minimize.
First make a long exposure photo with the lens cap on the
camera, at the same resolution as the photo you need to fix. If you do
this correctly, it will create an all black photo with your hot spots.
Next open both the photo you need to fix, and the second (all
black) image in Paint Shop Pro. Copy the second image (make that image
the active one, and press CTRL-C), and then paste that image as a new
layer on top of the photo that needs fixing (Make the photo the active
image, and press CTRL-L.).
The black image will now be on top of your photo. In the layer
panel, change the layer mode from 'normal' to 'difference'. Your hot pixel
should now be at least a lot less visible.
Sometimes (when the hot pixel appears in an area with aurora)
the 'exclusion' layer mode might bring better results.
Back to the menu.
3. Removing Noise
Before I go into the removal of noise by editing let me give
you a tip: set your digital camera at the highest resolution possible.
Memory costs are so low these days that it is not an excuse anymore to
shoot photos at web resolutions. Not just that, but shooting a photo at
an 640x480 resolution won't do you any good if you want to have it professionally
printed on real photo-paper!
Additionally, on digital cameras the noise is often just around
a 1 pixel size, so a simple re-size of the picture downwards can fix a
lot of noise problems. Of course, this is harder on photos originating
from film, as the grain size is usually larger compared to digital cameras.
There are commercial programs like Noiseninja and Neatimage that can aid a lot with removing noise. But, with some looking around, you can also find free alternatives, like Noise Remover for Gimp. See this before and after of one of my photos:
As you can see, it does a more then appropriate job of removing
noise while keeping the edges of objects, and the star, intact.
4. Underexposed Photos
Once
in a while I see someone trying to bring up detail in their underexposed
photos by using the Brightness filter. That is sooooo bad! This is the
worst filter ever invented! Instead of trying to increase the dark parts
you want to be brighter, it just makes the whole image brighter, and you
end up with a grey photo, like the one on the left here.
We want to use the Gamma filter instead. This works in a nonlinear
way, and leaves dark areas as dark as possible, and does not make all
bright areas flat white. See this before and after of the same photo from
Jan Kelderhuis:
To
get the result I first used Gamma with a setting of 1,7. Each time you
have to see again which settings work best. The green arc did come up
quite nicely, but the typical green was still gone, so I added some further
enhancements to get that up as well.
For even more control, you can use the curves tool, which
you can find in Paint Shop Pro from the menu: Adjust -> Brightness
& Contrast -> Curves. We will be using this tool more extensively
in the next tutorial. It allows you to edit the curves per color. For
this photo I selected the curve for the green color, and set some control
points as you can see here on the left, to enhance the green. This photo
was quite a hard one to get a reasonable result from!
5. Detail Enhancement
Take a look at the next photo, which was made by Annemarie
from the Netherlands. The photo has detail in it, and using the curves
tool it is possible to enhance those. Naturally, you can also use this
technique to enhance a photo which already looks quite good on its own.
This
photo has detail, but it is a bit washed out compared to the rest of the
photo. Using a tool called curves in Paint Shop Pro (or any other program
of your choice) we can enhance the detail considerably. The idea is to
bring up the brightness of only the areas that have the detail we want
to enhance, and leave the other areas alone.
Let's take a look at the curves panel which you can find
from the menu: Adjust -> Brightness & Contrast -> Curves
I always start with clicking both eye icons top right. This
will make the changes in real-time to the photo in the program so you
do not have to rely on the small preview images in this panel.
Then to the most important part of the panel, the black and
white graph with the red line. This is the area we will be working in.
The line represents the values in the photo. It starts from bottom left
for pure black, to pure white top right, with all values in-between.
If you click on this red line, you will be able to add points.
You can add a few of these control points, and then drag them with your
left mouse button up and down the graph. You see what happens? The dragging
of a point will intensify the corresponding values if you drag the point
up, or make them darker if you drag it downwards.
Our
goal is now to add a control point just before the brighter lines in the
photo, to 'anchor' the darker intensities we want to leave alone, one
right on the lighter values to be able to drag them up, and possibly one
after the lighter values of the detail to anchor all brighter details
we do not want to change (the stars in this case). Photoshop has a pipette
tool which allows you to click the areas you want to edit. This is one
of the benefits of a program that costs a lot more!
If you played enough with the curves described above, you
might end up with something similar to my curves on the image to the right.
Here is another example I did with a photo from Arno_Veenendaal
from the Dutch chat:
Once you familiarize yourself working with the curves tool, move on to using the curves per color channel for even more control.
6. Enhancing Colors
Controversial subject, should you change the colors as they
were captured by your camera/film? This is something many will never end
the debate over. Fact is, some films capture colors differently then others,
as do digital cameras. Also scanning in a photo on a flatbed scanner might
change the colors considerably. Let alone making mistakes with setting
the wrong white-balance. There are cases where you might want to enhance
the colors. For example this image made by Cheryl:
To get the result on the right I used the Vivid
Saturation plugin for Gimp. It is built specifically to enhance colors
on photographs, and often works in a more natural way then using the basic
contrast filter.
Another way to enhance colors is to manipulate curves, like
we touched in the detail enhancing tutorial. You can also work with curves
per color channel, for even more control. On the above example I used
the red curve to slightly enhance the detail in the reds.
Naturally you don't just need this technique to fix photos,
it can also work to improve photos that already look great on their own.
Note the purple nitrogen fringe, and enhanced oxygen green on this photo
from Bud Kuenzli:
This is one quick and very simple way to enhance the colors
in a photo. There are many other ways to change/add/enhance and otherwise
manipulate the colors in a photo. They can include filters that are available
in most programs such as Contrast and Saturation, but also filters that
have been written by the vendor specifically for that program. In my opinion
it will go to far to explain all these filters for this article, as it
would easily double the length of the article (and also my time to write
it), and would steer away from my goal, to get you up and running fast
with a few basic techniques! I encourage you to explore these further.
On the Net there are many tutorial sites for programs such as Photoshop
and Paint Shop Pro that can help you out. Happy exploring!
Back to the menu.
7. Sharpening Images
Sometimes a photo ends up not entirely in focus or it generally
misses a bit of 'crispness' to make it a lot better. Most aurora photos
also suffer from noise - since the lights are quite low in intensity,
we need to use longer exposure times, and also higher ISO/ASA values mean
more noise. Simple sharpening filters enhance this noise. Please note
we can't make the aurora itself any sharper using these techniques, as
they are usually quite blurry themselves. We can however, make buildings,
trees, and other elements more crisp.
See this side by side example, the original, and a version
with a sharpen filter from Paint Shop Pro.
OK,
the branches and horizon got sharper, but look at the enhanced noise in
the aurora and clouds! I used to have a complex workflow of only enhancing
the edges in a photo, and leaving the other parts alone. This involved
duplicating the layer, applying 'greyscale' and 'find edges' filters,
using that as a mask, and .. and ... Well, it was tedious!
Recently I found a plugin for Gimp
(plugin AND Gimp is free software!) called Smart
Sharpening, and basically, it is doing the manual task of finding
and enhancing the edges for me in one easy to use interface.
Once you install the program and plugin, you can find the
plugin from the menu: Script-Fu -> Photokit -> Smart Sharpening.
As you can see, there are just three sliders to determine how much sharpening
you want, and what the threshold is for finding the edges. I usually experiment
with using a new layer for each trial and see which settings work best
for that photo. In the end I got the result on the right here.