Intro

It possible to extract different components from a picture, like the color or the details (so we can sharpen the picture). To extract this information we first must produce the opposite information. To extract the color we first create a black and white version. To extract the edges we first blur the image.

Extracting the Details (A high pass filter)

1. open up a picture in GIMP
2. duplicate the top layer of your picture
3. blur the top layer. A blur of about 50 pixels is a good number to be able to easily see the effect happening.
4. Change the name of the blurred layer to lf for low frequencies. When we blur an image we remove all the details–the higher frequencies, and we are left with the lower frequencies.
5. Change the layer mode of the lf layer to grain extract.
6. Right click on the lf layer and select new from visible.
7. Rename this new layer to hf for high frequencies. This is where all of the details (edges) are stored
8. Change the layer mode of the hf layer (top layer) to grain merge
9. Change the layer mode of the lf layer (second from the top) to normal
10. Your done. You should be seeing the original image again.

This filter automates the entire process, and gives you the ability to split an image into multiple high and low frequency layers.

Extracting the color

You can continue on keeping the same layers used in the previous example, or you can do this on a new picture.

If you are starting from a new picture

1. duplicate the top layer of your picture
2. Make this layer black and white.
3. Name this new layer b&w

1. Make the lf and hf layers black and white. You should still have the colored background layer as the bottom layer
2. Right click and select new from visible
3. Name this new layer b&w
4. make the lf and hf layers invisible

1. Change the layer mode of the top b&w layer to grain extract
2. Right click on the top layer and select new from visible.
3. name this new layer color
4. Change the layer mode of this new layer (the top layer) to grain merge

1. Change the layer mode of the b&w layer (second from the top) to normal

In the second image I got rid of the green by using the luminosity color information.

Extracting other information

Any information can be extracted from an image, all you have to do is.

1. open an image in GIMP
2. duplicate this layer
3. manipulate the layer in some way
4. set the layer mode to grain extract to extract the manipulated information
5. right click and select new from visible
6. set the new layer to grain merge
7. set the middle layer to normal

A great use for this that hasn’t been described yet is to heal part of an image. This link, and this link (first link looks better) describe two different ways of healing an image by extracting information from it.

Another use is when you have you used a very time consuming filter, and then you would like to increase the intensity of the affect. Instead of having to wait for the filter to process again, you can use a layer with the filter applied to it, and a layer without the filter applied to it to extract the manipulations of the filter (if you don’t have two layers you can copy the layer, undo, create a new layer and paste). Once the information is extracted you just duplicate the extracted layer to increase the intensity of the filter, without having to process. This only intensifies the affect of the filter, you’ll have to rerun the filter to change any of the other parameters.

Miscellaneous Notes

When you extract information, you can use a neutral gray (128,128,128) to erase information on that layer.

If you mix the order of the layer’s you’ll get the opposite of the desired affect. Simply invert the extracted information to get the affect you wanted.

You can stack affects as many times as you want by duplicating the extracted information.

You can assert yourself that the process of splitting the image into layers hasn’t modified the image at all, by right clicking and selecting new from visible, and then check this layer against the original using the blend mode difference. you should see complete black. You can further verify that there are no differences, by creating a new layer from this black layer, and then select color->auto->normalize. If there were any part of the image that was a shade away from being pure black, the image would change to white, and the changed areas would be shown at a much higher intensity.

Further Reading

A great series of articles about low and high frequencies

The thread where I first learned about all this

Article similar to this one (They talk about removing the “luminous color” to give the picture a warmer look. I’ll have to try this out)

My final and best game. You are a cute little character called platy, making your way through this radically awesome platform game.

Please leave any comments, and criticism you have about this game in the comments.

Download

Your mission: collect all of the keys without touching the skulls.

Warning! I made the game a bit too difficult. You do however have the ability to esc back to the main menu and play any of the levels in whatever order you desire.

Download

Download

first pic: close up of original, second pic: color noise removed with bilateral filter, third pic: close up of final image

How We analyze the problem

Sharpening and noise reduction directly affect each other. When reducing noise, the picture becomes blurrier. Increasing sharpness can enhance noise, and create sharpening artifacts. Taken to the extreme, noise can be eliminated, and sharpness can be enhanced, at the cost of loosing all the details in an image. This is undesirable. We need to find an optimal solution that doesn’t blur the image too much when applying noise reduction, and doesn’t produce too many artifacts when sharpening. How much is too much depends on the image and personal taste.

When to sharpen and remove noise

If there is noise remove it, before processing the image. Color noise noise should always be removed. Some people like to keep luminous noise. If you want some noise you can leave some of this type of noise, but you should normally remove this too.

Unless you are going for a soft affect sharpening should be applied to an image. It is often said that you should do this as one of the final steps. It isn’t critical that you apply sharpening as the last step, just know if you don’t, the amount of sharpening applied can change, especially as tones in an image are manipulated. All of your noise removal should be done before you start sharpening.

Where to sharpen and remove noise

Often the luminance channel is the best channel to use, but sometimes other channels are better. Looking at the amount of noise on all of the channels will tell you which one is the best to use. I don’t usually spend time looking at different channels, for the most part the luminosity channel works well.

Noise removal

Using the filters described below I removed the color, speckled, and some luminance noise. There is still some luminance noise, and some bigger patches of noise in the image i.e. the white patches in the shirt. This noise can't easily be removed without destroying the image. I would have to go in and manually do some cloning, or use some other technique to remove this noise.

color noise

This noise is the most annoying yet it is very easy to remove, and does little damage to an image. In most cases all that has to be done is a bilateral filter on either the AB channels in lab mode, or the blue and red chrominances. The bilateral filter will blur the image while keeping the edges of objects from being blurred.

Sometimes color noise will come in large patches. The bilateral filter will be fooled into not blurring the patch of color because it wants to preserve edges. Fortunately the color channels can take a lot of blurring. For best results blur the patches that are causing you trouble. If you don’t want to take time to selectively blur part of the image, you can try different flow and blurring filters. The bilateral filter will also consider less of the image to be edges if you apply a small blur first.

luminance noise

Unlike color noise you need to be much more cautious when removing this type of noise. color noise should be removed first so that the luminance noise is easier to see. luminance noise is difficult to remove, and sometimes you may wish to only partially remove this noise to allow some of the finer details to show through. A few noise reduction filters are described below.

G’MIC’s anistropic filter

This filter blurs areas where noise could appear in a swirly anistropic like fashion. It’s sort of like a bunch of small paint strokes blurring the image. This filter keeps these “anistropic paint strokes” from crossing over edges. It is a good all around filter for reducing luminance noise. This link explains what all the sliders in the anistropic filter mean.

G’MIC’s Patch based filter

This filter doesn’t seem to remove noise that well, instead it blurs the noise into patches. It may work better if bigger patches are used, but the filter goes extremely slow if you try to do this. Use it to reduce noise into bigger but less noisy splotches.

bilateral filter

This filter eliminates detail and noise, but unlike a gaussian blur the edges of an image are preserved. Be careful, this filter is very destructive. Besides using this filter to remove color noise, it should only be used if you actually want to remove detail. This is often the case with shiny metallic or plastic objects.

G’MIC’s hot pixel filtering

This will remove the very bright and dark pieces of noise. This filter is best used when removing little pieces of noise. Recently I’ve found many of my pictures would benefit from this filter. whenever you see speckled noise that is very bright or dark, try this filter. I’ve also had some good luck with this filter at reducing big splotches of high contrasty noise. The filter was really slow when I did this.

wavelet denoise filter

This filter hasn’t seem to work that well, but recently I used it on a picture that had bigger patches of noise, and I found that this filter works well for removing big patches of noise.

Selective Gaussian blur

This is a more rudimentary filter, that I don’t normally use for noise reduction. The filter is the same as a gaussian blur, except that it will not blur pixels that blur more than a given threshold.

Other filters

I don’t normally use these filters, but they can produce some good results. These filters are the NL filter, the despeckle filter, and the median filter.

Sharpening

The most common sharpening filter is the unsharpen mask (USM) filter. A high pass filter is a USM filter before it is merged down. There is no difference. Photoshop’s smart sharpen filter is just a USM filter applied on the luminance channel only. As sharpening is mainly an operation done on the tones of an image, it is best to use the luminocity channel, so you don’t have the colors messing with the sharpening algorithm.

Most sharpening filters are applied to the edges of an image and to the details in an image to. If you only want to sharpen the edges you can use an edge detection filter, and then mask out everything but the edges. You will need to grow the mask a bit when doing this. If you don’t want to detect details the best edge detection filter is the adaptive edge detect filter. A version of this has been implemented in GMIC. Look under the contours section for different edge detection algorithms.

Manually applying a USM

It can be helpful to know how the process of a USM filter works. To manually apply a USM using Gimp

1. open up an image.
2. Duplicate the layer and blur it.
3. Change the layer mode to grain extract.
4. Right click on the layer and select new from visible.
5. change this new layer to grain merge.
6. Go back to the blurred layer. Changing the layer mode back to normal will give you the original image. Deleting this layer will give you a sharpened version of the original image.

This link explains how to manipulate the USM process to sharpen on specific layers, and to mask out everything but the edges when sharpening.

High Pass Filter

This filter is the same as an unsharp mask filter. Seriously. Every time you run the unsharp mask filter a high pass layer is created and merged down. Because the high pass filter gives you less control over the entire process, it is generally better to use a USM filter than a high pass filter.

A good technique is to use this filter on a layer that hasn’t had any noise reduction applied, and then move the high pass layer above all the layers that have had noise removed from them. This will allow you to recover detail that has been smoothed out from the noise reduction.

Shock Filter

This is one of my favorite filters for pictures that have a lot of noise. The shock filter sharpens without increasing noise. However it looks awkward when viewed up close. It creates this wavy pattern as it sharpens the edges of a picture. The first picture I showed of a bird has had a shock filter applied to the last image in the series. You can see the wave-like pattern along the edges of the bird.

RL Deconvolution Filter

This filter seems to enhance the little details and big details an in image evenly. This has the affect of enhancing any noise, so don’t use this filter in noisy images. In G’MIC this filter is simply called deconvolution.

Sharpening with Synthesis FILTER

This filter is very confusing. Using this filter will add a texture to the picture. There was one case where I used this filter, and it was superior to any other sharpening filters, but that case seems to be the exception. If you want to mess with this filter, you’ll need to first get the resynthesize filter. The filter leaves you with a very weird looking image. You’ll want to extract the high frequencies from this image. I will be talking about extracting high frequencies in my next article. The filter is also very time consuming. On my test image I found that a strength of 1 finely sharpened the image. A strength of 2 and 4 completely destroyed the image. A strength of 8 add a thick texture while sharpening the image. A strength of 16 and 32 added too much texture, and didn’t seem to be doing much sharpening anymore.

Sharpening by synthesis example. First Pic: Original image, second pic: strength of 1, third pic: strength of 8

Octave Sharpening Filter

This filter is similar to the unsharp mask. If I showed two images, one done with the octave sharpening filter and one done with the unsharp mask filter, there would be no way to tell the two images apart. It’s hard to say one is better than the other, the two filters are basically interchangeable.

Further Reading

Sharpening Tutorial from Cambridge in Color

Things to think about when sharpening

Manually Sharpening an image

 A technical article talking about sharpening in terms of frequencies

One of my favorite pictures. I used the techniques described below to manipulate the color in this picture.

Methods Of Changing Color

More control can be gained over an image by decomposing an image first and then manipulating the color channels. In Photoshop you can change an image into LAB mode, but I can’t figure out how to change an image into HSV or YCrCb mode. In GIMP it’s easy. Download the G’MIC plug-in, if you don’t already have this great plug-in. Once downloaded and installed open up the color category from inside of G’MIC and you’ll see a lot of filters for decomposing and manipulating different color modes.

Hsv(Hue Saturation Value)

Adding more contrast to the hue channel will create more hues in the picture. A bigger variety of colors! Adding less contrast will unify the colors to a more monochromatic image. For example if you have a background with a lot of foliage varying in different hues of green, you can unify the background by decreasing contrast. Changing brightness shifts the hue (changes color balance).

Increasing contrast in the saturation channel. channel actually doesn’t add more color to an image as you might think. More contrast will make the areas that have are most saturated even more saturated, and all the other areas become less saturated. Changing the brightness on this channel will add more saturation to the image.

The value channel is a black and white copy of the image. You can only change the tonal values of the image by changing the value channel. This is also true when decomposing to YCrCb and Lab. There will be one channel preserving the tones of the image while the other two let you modify the colors.

LAB(Lightness A-color B-Color) and YCrCb(Luminance Red & Blue Chrominances)

YCrCb and LAB split the color into two channels that when changed will have little or no affect on the tonal values of the picture. You can add contrast to one channel like the b color channel to make the yellows yellower and the blues blueer. decreasing the brightness in this channel will have the reverse affect. Changing brightness on a YCrCb chrominance channel will have an affect on more hues and will be more of a drastic color change. It sounds complicated, but there really isn’t much thought process in any of it. You just experiment around with different sliders and see how they affect your image.

Change individual colors

As Silvio mentioned in the comments Lightroom allows you to change the levels and saturation of individual colors. I use Raw Therapee to go through my raw pictures. It has a similar feature. I haven’t used it enough to be able to say too much about this feature, but it seems to be a powerful tool for changing the hue, saturation, or value of a specific color (red, yellow, green, cyan, magenta, and violet). In Raw Therapee this is done gradually, instead of using a threshold, keeping things looking natural when you edit color by color. G’MIC for GIMP has a similar HSV equalizer, but it is uniform in edits up to a threshold, so results look unnatural.

1st pic - original, 2nd pic - HSV Lab and YCrCb color changes, 3rd pic - final picture after tonal adjustments

Guidelines

Moderation

If all of the colors are overly saturated, then none of the colors will stand out. Changing contrast in the color modes talked about above can be used to selectively make part of the image stand out. Don’t overdue the color.

Create a mood

You don’t have to color balance an image to what is most correct. You should be changing the colors to replicate the mood you want to potray.

Warm vs cool colors

cool colors create a lonely cold mood while warm colors give an inviting feel to the scene. Contrasting subjects of a picture with warm vs cool colors can give an interesting affect.

The cool colors in this picture create a calm mood

golden hour

Often colors stand out the best at the time of day photographers like to refer to as the golden hour. See this article if your not familiar with the golden hour.

Change color locally

Using the techniques described above one can change the color on different layers, and then use layer masks to accent specific parts of a picture.

Further Reading:

• Great video series about manipulating color
• A website dedicated to the subject of color (Great site I am looking forward to reading through it)
• The G’MIC plugin
• Using Color in Photography
• Harvard Video about color spaces, how sensors detect color, calibrating devices, and other technical stuff. 

In an article about composition professional photographer Alain Briot said:

No amount of technology can make up for a lack of inspiration

- Cameras and other gear are technical

- Inspiration is artistic

- The two things exist on different planes

- Achieving a personal style in fine art means working as an artist not just as a technician

A few years with a crappy camera and a person who is dedicated to learning composition WILL produce better photography than the enthusiast who buys fancy equipment, expects good pictures to come, and then does little to achieve this goal. The crappy camera will produce crappy pictures, but the photographer will know how to compose his pictures better. with enough work his/her pictures could be worthy of fine art galleries, while the person who does nothing but take a few pictures with expensive equipment will have little more than some high resolution snapshots to stick in a family album.

If you still don’t believe me, let me tell you that I personally have experienced this. Not one of my pictures were taken with an SLR camera, yet I have a few pictures, not as many as I might otherwise have, but I have some really nice looking images.

In another article Alain Briot also said:

“Composing a good photograph is not easy. Teaching others how to create interesting compositions is even harder. In fact, composition is one of the most difficult areas of photography or of any visual art for that matter, so much so that my teacher, Scott McLeay, refused to teach composition. His only guidance in this matter was brief and succinct. He would simply explain that, in regard to composing a photograph, each part of the image is equally important.”

Although it is impossible for me to lay down rules on composing an image. This is something that differs for each photo and must be learned by experience. I can, however, give you a few suggestions on the types of things to look for when taking an image.

know your subject

Rule of Thirds

The rule of thirds is not an actual rule, it’s a guideline that you should be aware of, and then ignore. The rule of thirds dictates where the most interesting points in an image are, but this is far from being correct. On a blank canvas the most interesting pieces would be at the intersections created by dividing a picture in thirds, but in a picture there are many elements that nudge those points of interest in one way or another. Any of the other composition guidelines mentioned below will have a far bigger impact on your photo than this rule. When taking a picture compose the picture in the way you think would work out best, not at the intersections created by the rule of thirds. Images with a simple composition are the exception, these images can sometimes benefit from this “rule”

 

Golden Ratio and Phi Spiral

Same as the rule of thirds (see above point), but uses different intersecting lines to create points of interest. See this article for more info on how these rules work.

 

Off-centering the subject

Where to put the subject of an image is up to your own judgement, but try to avoid putting the subject in the center. If the subject is close to a point created by the rule of thirds, you could try to see if aligning the image this way produces a better composition. But try out other ways of aligning the image. If there are distracting elements on the edge of an image make sure they get cropped out, unless you plan on photoshopping them out later. When composing an image keep in mind any leading lines and eyelines(the invisible line created from a person looking in some direction). Eyelines are the biggest thing I keep in mind when cropping an image, they are a bit more difficult to think about when taking the picture if people are moving around in the image, but if you have someone modelling for you take their eyeline into account when taking the image.

 

centering the subject

I just said not to do this, but now I am saying to do this. You’ll often here that you should never center your subject, but this is not true. Most of the time it is true, but there are a few times when you should do this, mainly when you have a large amount of power or symmetry in an image. It is also often desirable to have a square crop with this type of picture. A square crop puts a lot of emphasis on the center, and keeps out parts of the image that don’t have as much power.

A great example of breaking the rule of thirds is the below image I took of some light trails.  When this picture is aligned by the rule of thirds it looks terrible, but when aligned along the center it looks much better.

The centered picture is much better than the picture that follows the rule of thirds

Make sure you understand that I’m not telling you to go shoot a bunch of pictures with the subject in the center. Rather I want you to know that there are times when a subject should be aligned in the center.

 

leading lines

See if you can align objects in a picture to create leading lines towards the subject. Leading lines will emphasize and add an interest to all the objects involved. An image with a leading line will cause the viewer’s  eyes to move along the line looking at everything in the line’s path. An image with multiple leading lines will cause the viewer’s eyes to lock in to the spot where the lines intersect. This can be a very strong way of focusing the viewer’s attention on the subject.

Let me also mention a very strong type of leading line; the eye-line created from a person looking in some direction. This is probably the strongest type of leading line.

 

Lines

The same principle as leading lines apply to lines created at the edge of an object. These lines are stronger then leading lines, and as a result, care should be taken that they are straight with an edge of the image or are pointing towards the subject, or are in some way helping the composition of the image. These lines can be the subject too. This is often seen with an image that has a road going down the middle of it.The road and the lines associated with it are the subject.

 

winding lines

A winding line creates a sense of movement and can be useful in trying to convey a sense of motion. Leading lines can also be curved, this is usually done by having a series of straight edges that form a curve.

 

framing

An image can be framed by doorways, arches, branches, etc. Framing an image helps create a sense of depth. When using objects to frame an image, make sure the frame is simple, and doesn’t overpower the image. Unless you want the frame to be the main focus of the image, in which case make sure the objects inside the frame doesn’t overpower the frame.

 

hue/value/saturation

Many people think that the hue/value/saturation should be change to be as close as possible to the way your eyes perceived the scene you took a picture of. I am of a different opinion, and I believe most professional photographers would agree that these should be changed to create the desired mood that you want an image to have. If you want an image to have a cozier feel go ahead and shift the image to a hue that’s warmer than what your eyes saw when you took the picture.

hue/value/saturation can also be modified locally(to selective parts of an image) in post-processing. This is an excellent way of drawing the attention of the viewer to the subject of your picture. When done subtly, the effect is unnoticeable to the casual viewer, but they may notice how they are drawn to some part of the picture. When done more extremely some people may cry out that the picture has been over processed, while other people will absolutely love the picture.

 

Depth of Field

Obviously keeping something in sharp focus is going to make it stand out from everything else. Be careful about out of focus areas in the foreground as they can often be distracting. Sometimes the out of focus area can be a main part of the picture. This is can happen if you want to shroud part of the picture in mystery.

 

edges

In the beginning of the article when I quoted Alain Briot he mentioned that his teacher Scott McLeay would say that each part of the image is equally important. Don’t forget the edges of a picture they are just as important as the rest of the picture.

 

cut Off people’s Limbs at appendages

If you must crop out a body part, remember that the missing body part will distract the viewer more if you don’t crop at an appendage.

 

simplicity

This guideline is often seen. It is actually comes from a higher overarching guideline that I talk about  in my first point ‘know your subject’.

 

keep horizon straight

It doesn’t have to be kept straight to the edge of the picture, but it does need to be kept straight to some point of interest. Don’t leave the horizon slanted a few degrees. You can make big tilts to the horizon, if that is the affect you want to create(DO NOT do this to landscapes).

 

Frame Tight

Getting closer to the subject will put an emphasis on the subject but at the same time…

 

negative space can be interesting

…Having a lot of negative space adds serenity to the picture’s mood.

 

eyes are important

When placing a person in a photograph, align their eye’s with a focal point within the picture.

 

bottom right corner

Of the four corners in an image this is the most interesting corner. This only applies to those of us who read top to bottom, left to right.

 

Lighting

This is very important. very very important. I won’t say much about lighting as that is a topic for a different article, but don’t forget to pay attention to your lighting.

Mood, Message

Remember when creating a composition, there is no single right way. It all depends on the mood and the message that you are trying to portray. There are many wrong ways to compose an image, and It takes skill to spot a correct way. Try to stay away from composing an image in the same way as everyone else. Be new. Be creative.

 

Viewpoint, positioning yourself

Move around and find a way of composing an image that you like. Try taking a picture from down low, up high, far away, in close, from the left, from the right, etc.

 

Symmetry and Patterns

Symmetry and patterns stand out when introduced unexpectedly in a scene. This work best when there is a sleight difference in every pattern in a scene, allowing the viewer to compare and contrast the repetitious objects.

 

Lenses

Use a wide angle lens to increase depth, and focus attention away from the edges. Increase it even more with a fish eye.

Use a normal sized lens for a natural feel.

Use a telephoto to compress the depth, and to give the edges more of an emphasis.

Or fake the lens-distortion in post-processing.

 

Depth

Use the appropriate type of lens for the feeling of depth that you want to create. Depth can also be created, or taken away, by a foreground-background realtionship. Make sure there is some kind of relationship when you add a foreground and a background element to a picture.

 

Further Reading:

•  15 Short thoughts on photography from Alain Briot
• Alain Briot’s nine part series on composition!
• Thinking about composition in terms of negative space instead of the rule of thirds
• Thoughts and intriguing pictures about symmetry and patterns
• 10 good composition guidelines
• Some thoughts from Alexander Buisse about image composition