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Understanding Digital Camera Sensors
A digital camera uses a sensor array of millions of tiny pixels in order to produce the final image. When you press your camera’s shutter button and the exposure begins, each of these pixels has a “photosite” which is uncovered to collect and store photons in a cavity. Once the exposure finishes, the camera closes each of these photosites, and then tries to assess how many photons fell into each. The relative quantity of photons in each cavity are then sorted into various intensity levels, whose precision is determined by bit depth (0 – 255 for an 8-bit image).
Each cavity is unable to distinguish how much of each color has fallen in, so the above illustration would only be able to create grayscale images. To capture color images, each cavity has to have a filter placed over it which only allows penetration of a particular color of light. Virtually all current digital cameras can only capture one of the three primary colors in each cavity, and so they discard roughly 2/3 of the incoming light. As a result, the camera has to approximate the other two primary colors in order to have information about all three colors at every pixel. The most common type of color filter array is called a “Bayer array,” shown below.
A Bayer array consists of alternating rows of red-green and green-blue filters. Notice how the Bayer array contains twice as many green as red or blue sensors. Each primary color does not receive an equal fraction of the total area because the human eye is more sensitive to green light than both red and blue light. Redundancy with green pixels produces an image which appears less noisy and has finer detail than could be accomplished if each color were treated equally. This also explains why noise in the green channel is much less than for the other two primary colors (see “Understanding Image Noise” for an example).
Note: Not all digital cameras use a Bayer array, however this is by far the most common setup. The Foveon sensor used in Sigma’s SD9 and SD10 captures all three colors at each pixel location. Sony cameras capture four colors in a similar array: red, green, blue and emerald green.
Digital Photography Tutorial and Tips:
Digital photography has become the medium of choice for both professional and amateur photographers in recent years. Most of the content of these tutorials applies equally to either digital or film photography.
Modern digital cameras, and film cameras, take care of the technical details for us, but because of this, rather than in spite of it, our brains are lulled into non-thinking, automatic
mode, we think the camera is going to do it all for us. The most important pages of this site, therefore, are the photography tutorials.
On the photography tutorials page you will find an introduction to the articles which cover many aspects of photography both artistic and technical, or you can just wade in and start reading using the menu on the left.
If you are not a big reader or just want a ‘quick fix’ solution to a problem, try the Top Ten Photography Tips page first.
I have been giving some thought recently to what you’re going to do with all those photographs that you have taken. Once you start getting some good pictures that are of interest to others there are plenty of opportunities to make a bit of money selling them online. Have a look at my article Making money from your Photographs for some ideas on how to get started.
Free Photography Tips
1 Selection
Select only the best of your pictures to show to others and leave the rest in the drawer. Showing someone every picture you have taken dilutes the effect of the best pictures and gets very boring. You may want to show twenty pictures of little Johnny at the park because they are all quite good and you can’t decide which are the best but, trust me, you will be better off making that decision and showing only the few good ones. – go to Selecting Photos
2 Turn the Camera on it’s SideAt first it feels awkward holding the camera on it’s side, but it is worth getting used to. If the shape of your subject, a person or a building, fits into an upright rectangle, you waste so much picture space if you shoot in landscape. You paid for all those millions of pixels, don’t waste them. – go to Cropping and Framing
3 Framing
One of the easiest ways to improve your photography is with careful attention to framing. Look into the corners of the viewfinder to see what is there. Do you need all that background? Can you get closer to your subject or zoom in? – go to Cropping and Framing
4 Direction of LightingPhotography is all about light, the direction of the light falling on your subject is most important, you must look at your subject carefully and see how the shadows fall.
If you are able to choose the time of day to shoot your pictures, try to pick a time when the sun is low in the sky, either shoot in the early morning or late afternoon. Shooting pictures of people with the sun too high in the sky, tends to mean the subject’s eyes will be in shadow and/or your subject will be squinting in the strong light, both of which tend to look horrible. A nice side effect of shooting in the early morning or late afternoon is that the colour of the light is ‘warmer’, reds and yellows are stronger which generally gives a more pleasing effect.
If you are photographing in sunlight, try to position yourself so that the sun hits your subject from the side, this will give you nice ‘modelling’ and help create a 3D effect in the picture.
Sunlight behind the subject can give a very pleasing ‘backlight’ effect but be careful that you are not getting ‘flare’ in the lens, which degrades the contrast of the image. – go to Photography in Sunlight
5 Direction of Lighting (2)The very worst kind of lighting is provided by the little flash fitted into all modern cameras. Not only does it give your subjects the dreaded red eyes, but also flattens all faces into shadowless featureless blobs. Use the in camera flashlight only in an emergency, when there is no other choice.
6 In Camera FlashWhen you have to use the in camera flash, keep your subject(s) away from walls, especially light coloured ones, if at all possible, and avoid that ugly black shadow which looks like an outline. This will not show up against a dark background.
7 ExposureUsing auto exposure to your advantage.
If you have a modern camera, the chances are that the default metering system is ‘centre weighted average’, which means that, although it takes an average reading of the whole scene, it takes more notice of what is in the middle of the frame. Which is good news for us. The other good news is that it takes this reading at the time when you take ‘first pressure’ on the button to take your picture. When you push it halfway down and it beeps at you, not only is the focus now set (on an auto focus camera) but the exposure reading is taken and the aperture and shutter speed are set. So, if your main point of interest is not in the centre of the frame, it’s a good idea to put it there temporarily while you focus and take your light reading, then move the camera whilst still holding the button halfway down and compose the picture the way you want it to be. A common use for this technique is when you are taking a close up shot of two people and there is space between their heads, if you’re not careful the camera will focus on the wall or trees behind them. If the background is very dark or very light this can alter the exposure significantly and result in faces that are too dark or too light. – go to Exposure
8 Shutter Speeds
When the shutter speed is important as with moving objects, it’s a good idea to set the camera to ‘Shutter Speed Priority’ mode. This is where you select the shutter speed and the camera selects the appropriate aperture according to the light reading. – go to Shutter Speeds and Apertures
9 Apertures
If depth of field is important to either make sure everything is in focus or to throw some things out of focus, select the ‘Aperture Priority’ mode on your camera. In this mode you select the aperture and the camera selects the shutter speed according to the available light. – go to Shutter Speeds and Apertures
10 Neutral Density Filters
If you are shooting in bright light and want to restrict the depth of field, use a neutral density filter in front of the lens to reduce the light entering the lens. These are available in different densities, 2x, 4x, 8x etc. each one cutting the light in half, quarter, eighth etc. In extreme circumstances you can screw a couple of them together. Although they are ‘neutral density’ filters and should not effect the colour balance, if you use two or more together you might need a little colour correction at the printing stage. – go to Shutter Speeds and Apertures
Photography tips for beginners
This site shares some ideas to make better photos. It is intended for you as a beginning photographer or more advanced photographer. The ideas are worked out in tips for several photography subjects.
Before going to our own ideas from dptutorial (with oddities and extremes), you should know there is a pretty standard list of useful tips. Here what we think that every beginner should learn as basics and every advanced photographer at least should keep in mind:
Choose a subject or message of your photo. If there is no clear real subject, nothing of graphical interest and no mood to convey, it is probably not an interesting photo.
Remove things that don’t add to the photo. Especially if they detract from the central message. Don’t only know what to include, but also what to exclude. Find a simple background and look for balance.
In this example the hand of the woman below and the colorful yellow and blue shirts are distracting elements. Waiting until the hand is gone and standing a few steps more to the left, so the people in the back are out of the frame, would both improve the photo.
Don’t be afraid to zoom in or get very close. The most common mistake is that photos are taken from too far away and that there is just too much environment that doesn’t add to the message. Filling the image with the subject underlines what the intended subject is, and removes cluttered background. It achieves simplicity.
Don’t automatically center your subjects. Beginning photographers massively center their main subjects on their photos. This is not illogical because the photographer aims at the subject with the camera viewer. If you rather place the subject outside the center it will often result in a more dynamic composition. Experiment with that.
A popular guideline is the rule of thirds. Imagine the frame divided into thirds, both vertically and horizontally, like a tic-tac-toe board. Then place the subject on or near one of the lines or intersections. This is called the rule of thirds, or the ‘golden mean’. However don’t follow this rule slavishly.
Remember that the eyes are most important for people and animals. When zooming in and the head fills the image, the rule of thirds applies to the position of the eyes.
Be sure to hold your camera level. It will break the strength of your photo if the horizon appears with an apparent angle.
Sometimes photo opportunities appear in a split second, and you have just no time to control the angle of your camera. When at home your photo appears to be tilted, no problem. With imaging tools it’s easy to level the photo afterwards. However this gives a small loss in image quality. So practise your reflex to hold your camera level in the first place.
Eyes are exceptionally important. They tell the story. When photographing people and animals everything else can be hidden or cropped out: the mouth, the nose, the hair. But the eyes must be visible.
In addition, the eyes have to be tack sharp. Unsharpness of the eyes will hurt the attraction to the eyes, and with that the quality of the photo. If the eyes are not sharp, the photo doesn’t look sharp.
Watch the distance with flash. Don’t bother using flash over 30 feet away. Most non professional flashes just completely don’t function at this distance or greater. Flash works best with nearby subjects. When taking a scenery of a bridge at some distance, flash won’t help. Instead of flash, use longer exposure times and a tripod or, if necessary, a higher iso setting.
When photographing multiple people with flash, be aware that persons that are close will be illuminated by the flash much more than persons further away. So if you want all of them as prominent, have all at the same close distance from your camera.
As a rule make use the full range of luminosity: from completely dark (black) to completely white. This makes photos dynamic and vivid.
On the other side don’t over expose with digital camera’s. The information of over exposed parts of the image will be lost definitively and can’t even be recovered by imaging tools. Under exposing is also unfortunate. Image tools can light up the darks and make the tonal visible, however with some or even considerable noise.
Directly after taking a photograph, reading the histogram can be helpful. If the histogram is pegged against the right end, the photo is over exposed. When pegged against the left hand, it is under exposed.
But adjusting the settings of the camera to capture the whole full range of luminosity without over or under exposing can be quite a struggle. Just be sure not to overexpose. Adjusting levels afterwards with an imaging tool will be the rescue.
Make a selection of your photos. Don’t put all your photos, complete with all the flawed versions of the same scene, in your (online) photo album. The bad ones harm the attention that the best ones deserve. Make a critical selection of your photos, keep the very best. This will enhance your the overall quality of the album enormously.
The tree growing out of the subject’s shoulder or head is a classic photographic syndrome.
As you position yourself for the photo look out for power poles, lamp posts and other objects behind the subject that can ruin your photo. When it happens, reposition yourself or the subject.
Also avoid objects in the background that visually merge with the subject because they have the same color. Let the subject be free-standing.
Digital Photograpy
Photoxels is first and foremost a digital photography site where you will find digital photography tutorials written in easy to understand language. Our One-Pager™ digital photography tutorials will help you select the digital camera that is best for you and make sense of difficult technical concepts.
Each digital photography tutorial is short, can be read in one sitting, and is immensely practical — which means you can put what you have just learned to use immediately. Enjoy!
Near Infrared Digital Photography
Near infrared light consists of light just beyond visible red light (wavelengths greater than 780nm). Contrary to popular thought, near infrared photography does not allow the recording of thermal radiation (heat). Far-infrared thermal imaging requires more specialized equipment, and is not the subject of this tutorial. Infrared images exhibit a few distinct effects that give them an exotic, antique look. Plant life looks completely white because it reflects almost all infrared light (because of this effect, infrared photography is commonly used in aerial photography to analyze crop yields, pest control, etc.) The sky is a stark black because no infrared light is scattered. Human skin looks pale and ghostly. I have a photograph of a friend’s black shirt, which looks white in infrared. My dark sunglasses all but disappear in infrared because they don’t block any infrared light, and it’s said that you can capture the near infrared emissions of a common iron.
Infrared photography has been around for at least 70 years, but until recently has not been easily accessible to those not versed in traditional photographic processes. Since the charge-coupled devices (CCDs) used in digital cameras and camcorders are sensitive to near-infrared light, they can be used to capture infrared photos. With a filter that blocks out all visible light (also frequently called a “cold mirror” filter), most modern digital cameras and camcorders can capture photographs in infrared. In addition, they have LCD screens, which can be used to preview the resulting image in real-time, a tool unavailable in traditional photography without using filters that allow some visible (red) light through.
This tutorial will take you through all of the steps necessary to procure and manipulate near infrared photographs through the use of a digital camera (or camcorder). You will need:
- a digital camera
- a Kodak Wratten #89B, #88A, #87, #87B, or #87C filter(in order of how much visible light they block, from low to high)
- a tripod
- a means to fasten the filter to your camera
- an image editing program such as Adobe Photoshop
Before we begin, you will need to check to see if your camera has an infrared blocking filter (also called a “hot mirror” filter) installed. A quick way to test this is to see if your camera can see beams emitted from a common infrared remote control. These beams seem to be fairly bright and are easily seen in a camera’s LCD preview area. If you don’t have an LCD on your camera, your only hope is to try to capture the beam by taking a picture of your remote (while depressing a button on it). If you cannot see the infrared beam, you may have to remove the infrared blocking filter by disassembling the camera. Note that this may void the warranty. Most brands of digital cameras are known to be sensitive to near infrared light.
Get a few different types of filters to play with. A #87C filter will filter out all visible light, but since these filters gradually filter out more and more light as the wavelength increases, the #87C will also filter out a good amount of the infrared light you’re trying to capture! I use the #87 filter because it filters out all visible light, but still lets in enough of the infrared spectrum for clear crisp images. The #25 filter lets in a significant amount of red light, and is often used in traditional photography because it allows image previewing through the viewfinder. These filters do not work well with digital cameras. Supposedly, you can buy a visible light filter from Edmund Scientific for $5, but I’m guessing that it’s not of very high optical quality. (609-573-6250, ask for a 1″ diameter circular filter, part no. H43948)
Here’s a table of % light transmission at different wavelengths for a few of the filters specified above. You should be able to figure out the approximate behavior of the other filters by comparing them to this table.
Night photography tutorial
It’s that time of year when you leave for work in the dark and return home in the evening in the dark, so it’s understandable that your camera may only surface at the weekend. But it doesn’t have to be this way. Many cameras, whether compact 35mm, digital or SLR, have a shutter speed range that will allow low-light pictures to be taken so you can venture out in the evening. The only requirement is a little knowledge of metering and some form of support to ensure that you don’t get blurred pictures as a result of camera shake.
The first thing to do is check that you can override the camera’s automatic flash. Most 35mm and APS compacts have a symbol that has a lightning bolt within a circle with a 45 degree line through it – just like a no entry road sign. This turns off the flash and ensures the camera makes use of its long exposure setting. You can check to see what the long shutter speed is in your camera’s instruction book. Digital cameras have a similar mode, although on models like the Nikon Coolpix 995, Sony DSC-F707 and Minolta Dimage 5 and most makes of SLR you just leave the flash in its down position and ignore the warning light telling you to activate flash.
Blackpool is famous for its illuminations and fortunately it has a pier so you can get far enough back to shoot the illuminated tower and the sea front. Rest on the railings and step the shutter down one stop to allow for the large area of darkness that will fool the meter.
Photography – Lighting
There have been entire books written on one very small aspect of lighting or another, so to do the subject justice in just a few pages is not easy, however I will do my best.
Although I have divided the subject up into different categories, the lighting you ‘find’ and the lighting you create for yourself, it is really the same thing. You need to manipulate the scene to create the effect you want, this might mean moving a light on a stand or moving your subject relative to the sun, or waiting for a better time of day to get the effect you want.
I once met a landscape photographer who, having found the scene he wanted to photograph, would pitch his tent and wait for the light to be right. Sometimes this would take two or three days. I’m not sure I would have that kind of dedication and I certainly don’t have that amount of time, but it is worth spending a little time getting it right.
Hi, interesting post. I have been thinking about this topic,so thanks for writing. I will certainly be coming back to your site.