Hot answers tagged artifacts
34
Moiré is a form of aliasing whereby false patterns can be observed in an image.
Imagine a lighthouse which sends a pulse of light every 5 seconds, and a camera (or other observer) which sees the lighthouse for three seconds and is then blocked from seeing it for three seconds:
lighthouse: *....*....*....*....*....*....*....*...
observer: ...
26
In digital photography, the moiré effect stems from interference between fine detail in the scene, and the grid of sensels in the sensor. You can also get a moiré pattern when scaling a picture down for display -- in this case, the interference happens between the fine detail in the picture, and the grid of pixels in the display.
Either way, you can get ...
23
Noise is often defined as any deviation from a "pure" signal. The signal is taken to be brightness pattern of the image so any variation in the pixel values that represent the image is noise. These variations arise principally due to:
Shot noise. The random way photons are emitted from a lightsource causes random variations in image brightness. The fewer ...
20
The simple answer is in order to get non-fake looking HDR, or good looking tasteful HDR you have to put lots of work in.
If you entrust artistic decsisons to a computer program the quality is going to suffer. So expect to take a considerable amount of time in your tonemapping software adjusting the settings, and remember that's not the end of the process, ...
20
The key to a good hdr photo is to use the correct amount of processing for the feel you want to achieve.
If your goal is to get the "hdr look", then you're probably doing it about right, because there should be a slightly "fake" feel.
If you are only using hdr as a method to improve a photo, then just be careful and try to under-process it. If you can't ...
18
Some dust spots on the sensor will absolutely not shift with air-pressure (blowing) alone. To shift them you need to wet clean the sensor.
I was nervous the first time I did this as I can understand most people would be. But it is not that difficult or risky, basically it involves wiping the sensor assembly with a soft rubber "wand" with a cleaning fluid ...
16
I'm willing to bet that that's dust on your sensor, not on the lens.
If you stop down to f/22, that can help to confirm that assertion, one way or the other. My sensor dust would really show up at the smaller apertures.
If they are indeed on the sensor (and they really look like the dust spots I got on my d70 and d200), you can try some of the Visible ...
16
This is lens flare, where reflections within the lens end up showing on your photos.
General guidance to minimise it includes:
Avoid getting the sun in shot (and ideally, avoid having it just-out-of-frame too)
Use a lens hood to shade the front element
Try to use lenses that have anti-reflective coatings
Keep the front element clean, but follow the lens ...
15
This looks like the effect of noise reduction at high ISOs. Heavy NR is common in compact cameras with small sensors. Fujifilm does it better than most, but there's only so much blood you can get from a stone.
On most modern high-megapixel point and shoot cameras, you'll see this even at low-ISOs if you pixel peep. It's important to note that in most cases, ...
14
What you're seeing in that shot is overexposure. Unlike overexposure in a day time shot,where the blown highlights tend to go pure white, the red light from the sign caused overexposure in the just the red channel. Thus all the different tones of red have become 100% red and detail is lost.
It can be fixed by reshooting at a faster speed / smaller aperture ...
13
This isn't uncommon to see when you have a UV filter attached to the lens which, generally, a lot of people do because it gets recommended by the camera store as lens protection. If you want a really detailed explanation, there's one on Luminous Landscape showing and explaining the issue.
My take, and it's a personal opinion, is to lose the UV filter if you ...
13
Looks like there was some dust or watter droplets or whatever in the air and that they reflect the flash light. The effect is not very present but as your background is black you can see them. Furtehrmore as they are out of focus they appear as disc rather than dot (in fact you got nice bokeh)
12
This looks to me like it might be dust spots or speckles on the lens, which are getting highlighted by the reflection of the flash back onto the surface of the lens.
Obvious first step: try cleaning the lens with lens cleaning fluid / wipes.
If this doesn't work, we might need more information. You mention this happens when using the flash with the Digital ...
12
If you save a JPEG image with an extremely low quality level, you WILL get compression artifacts. Its just a simple fact of JPEG lossy compression. If you wish to avoid compression artifacts, use a higher quality setting than 2. You won't need to save at maximum quality, as most images can be saved with a fairly low quality setting without noticeable loss in ...
12
You're exactly right — it's the same thing as a monitor pixel error, but on your camera's sensor rather than on an LCD screen. *
You can either fix it in post-processing (automatically, with many RAW-processing packages) or have it mapped out with the camera's firmware.
If you're lucky, your camera model includes a built-in feature to do that yourself in ...
12
JPEG actually uses two types of compression, a lossly and a lossless one. Lossless compression doesn't cause artifacts, so we can ignore that part. The particular type of lossy compression in JPEG, called a discrete cosine transform for the math knurds, allows a tradeoff between compression ratio and fidelity. Most software sufaces this as a "quality" ...
12
What you're seeing is longitudinal chromatic aberration (otherwise known as axial colour), whereby the light at the edge of the bokeh disc undergoes a colour shift depending on whether it is in front of or behind plane of focus. The reason for this is that light of different wavelengths focus at different distances along the axis of the lens.
This is very ...
12
That is the result of using the H4D-50MS in multishot mode with an uncontrolled subject. Notice that everything that is absolutely still comes out just fine, but anything that moves, even slightly, shows registration problems. The vehicle is most obvious since it's moving at a decent clip, but the motion is also visible in the water, grass, and so forth.
In ...
11
Looking at the original at http://i.stack.imgur.com/NC5Ft.jpg - the pattern is caused by an obstructing diamond-mesh fence in the lower part of the photo. The 'brownish diagonal line' across the lower-third appears to be twisted two-strand wire, holding the mesh up.
The fence, being much closer to the camera than the subject, is outside the depth of field, ...
11
Those are almost certainly reflections from the UV filter. I recommend taking it off.
This is a topic of much debate, but the fact is filters do cause artifacts visible in your photos — you've got the evidence right there. You can get better results from a more expensive filter, but then it'll cost almost as much as your lens. Lenses aren't as fragile as ...
10
The effect is caused by diffraction. Typically this occurs stronger at smaller apertures - open your aperture (use a smaller f/number) to reduce the effect.
The shape of the star is caused by how many blades your aperture has. A lens with a rounded blade aperture should also reduce the effect.
You can read some basic, non-super-technical information ...
10
Those look like features of the glass windows that are being revealed by the polarizer. I don't think there is any way to avoid them other than by not using the polarizer, or being careful with the filter orientation and lighting.
I've observed this effect many times in car windows. I can't find a technical explanation but I imagine it's to do with stresses ...
10
Looks like a shutter malfunction (which fits with it only appearing at certain shutter speeds). The shutter is made of a series of metal blades, it looks like one of these blades is misaligned, which is exposing that part of the sensor for longer than it should be, hence the bright area.
You can have the shutter replaced at a Canon service centre.
10
Looks like a hair on the sensor. Use your camera's built-in sensor cleaning function to see if you can dislodge it. If that doesn't work, you may have to clean it manually or take it to a camera shop that offers such a service.
Dust or hairs in the lens won't show up in photographs as they are too far from the plane of focus to be visible; have a look at ...
9
The 580EX should be fired in perfect sync with the 7D. Definitely when below sync speed. You seem to have a lag in your system here so the flash fires a fraction of a second after the 2nd curtain starts to close.
UPDATE - just noticed that the flash is actually mounted on the light stand and shoots through the umbrella - and it looks like you are using a ...
9
JPG compression is done in blocks of pixels. In a highly compressed JPG image the edges of those blocks can be seen: in the original image two pixels may have been very close in brightness and color, but if they are in different blocks, then after compression and decompression (when viewed) each of their values may differ from the original, so you lose ...
9
An example
Using the current photo of the week image. This is the high-quality JPEG:
re-saved in Gimp with JPEG quality 80 (low); please note the general loss of sharpness, "dots" around high-contrast edges, loss of detail in low-contrast areas:
and re-saved in GIMP with JPEG quality 30 (very low); please note evident 8x8 blocks and severe loss of ...
8
You can get all sorts of interesting shapes and colours when shooting directly into a lightsource like that. All pieces of glass reflect a certain amount of light and transmit a certain amount, so you actually get flare from everything in your scene every time you shoot, only it's usually much dimmer than the rest of the picture so you don't see it.
When ...
8
I know mattdm's answer has already been accepted and that focal plane shutter effects are real, but that is not what is happening here. As mattdm said, a focal plane shutter causes distortion because different parts of the frame are exposed at different times. For a spinning blade that moves a fraction of a rotation during the entire exposure, the blade ...
7
Camera Shake and Overexposure
As well as overexposure, I believe there is some camera shake (look at the lighted windows to the left), which will tend to turn anything into a blob.
Camera Shake
I'm guessing that in order to try and get enough light in for this mostly-dark scene, your camera slowed the shutter right down.
When the shutter is slowed down, ...
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