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983 reputation
716
bio website
location ND
age 31
visits member for 2 years, 6 months
seen 8 hours ago

Mar
17
comment Photo stretched at corners?
... projections e.g. in Hugin. What they often call "distortion free", meaning no barrel/pincushion distortion free, is projecting through a point. This is what the idealized thin lens (from middle-school optics) does. It has the property that straight lines in 3D get transformed to straight lines on the photo, but it also "stretches" the corners. This stretching (illustrated in the OP's photo) has nothing to do with "barrel distortion", which refers purely to those lines not being straight any more.
Mar
17
comment Photo stretched at corners?
Actually if the lens has more barrel distortion it will usually have less of this "stretching" (perspective) effect. "Distortion" (while standard terminology) is not the best word for these phenomena, as it implies that the picture doesn't show the subject "true to life", but in a "distorted" way. What actually happens is that the lens needs to project (part of) a sphere (spherical view) onto a plane (the photograph). There are many ways to do this, each with different properties. You can experiment with transforming a photo to various ...
Feb
24
comment Does a larger sensor resolution increase the difficulty of shooting hand-held?
The area ratio is not 2 but 1.5^2 = 2.25 and these two particular sensors have identical pixel pitch. That aside, doing any kind of comparison like this doesn't make sense unless you also talk about what focal length lenses are used on both. If the field of view is the same for both, then the higher resolution sensor will be able to detect smaller motion blur. If the focal lengths are the same for both (and thus the field of you will differ if the sensor sizes are also different) then the smaller pixel pitch sensor will be able to detect motion blur more easily.
Dec
22
comment Demosaic data stored in TIFF
@mattdm Then instead of voting to close, you can vote to migrate it to the right place ... the problem came up in a practical application to photography, so I thought it's more likely I'll find an answer here than on DSP.SE, as more people here would want to do the same thing here. Looking at the other questions on this site I don't see why this is clearly off topic if asking for say noise reduction software is not off topic.
Dec
22
comment Demosaic data stored in TIFF
@mattdm It's not about programming, nor about image processing methods. The question is asking for a software tool to do something, like many other questions on this site.
Nov
14
comment What is the precise definition of SNR, as used by DxOmark?
That is not my question... It is clear to me why a larger sensor will show less noise when its image is viewed at the same size as the image from a smaller sensor. What is not clear is the precise meaning of the numbers DxO uses.
Nov
14
comment What is the precise definition of SNR, as used by DxOmark?
This is a general definition of SNR, but not the whole story. It doesn't explain why a large sensor with more pixels will have a higher snr than a smaller sensor with the same pixel pitch but correspondingly fewer pixels. The standard deviation alone is independent of the number of pixels for a give per pixel noise level. Please see my comment on the main question.
Oct
1
comment Do official extension tubes degrade image quality?
... not have the same performance for closer objects. This much is clear from physics and geometry. Whether this does have a tangible effect in practice, when one uses an extension tube to allow focusing on objects closer than the lens was designed for, I do not know. The effect may be negligible. I do have a subjective feeling that one telephoto lens I use does not perform as well close to the minimum focusing distance as for distant objects, but that's just a subjective observation that I have never tried to test rigorously.
Oct
1
comment Do official extension tubes degrade image quality?
Image quality is a function of the object distance too though. It is impossible to create a lens that will map any one point (the object) into a single point (image). It's possible to design a lens which maps one particular object point into a perfect image point, but it's impossible to create one which maps all object points into perfect image points instead of smudges. (Think about mirrors: for objects at infinity you need a parabolic one, for closer objects you need an elliptic one.) So theoretically if a lens is optimized for objects beyond a certain distance, it may ...
Sep
19
comment What are some Chinese/Asian photo sharing websites similar to Flickr?
@Alendri And even when/where it is not blocked (it changes from region to region within China), it is simply unusably slow, like many other non-Chinese sites.
Sep
13
comment Demosaic data stored in TIFF
@PatrickHurley I have a single channel which looks like no. 2 here. I'm looking for a tool that'll reconstruct no. 4. I'm not looking to implement it myself.
Sep
13
comment Demosaic data stored in TIFF
Use case: same as here.
Sep
12
comment What Windows software can assemble a sequence of photos into a timelapse?
ffmpeg can do this. It's a command line program that works on all major platforms, including Windows. I have used it on Windows to assemble a time lapse. It's free and relatively easy to use (compared to other command line alternatives).
Sep
7
comment Canon 70-200 f2.8 non IS or f4 IS
Take a look here and here
Sep
5
comment Does shooting RAW vs JPEG have a significant effect on battery life?
You don't lose quality by shooting JPEG. You only lose some flexibility of adjustment. Since the result is downscaled anyway, even a small size JPEG is good enough.
Sep
5
comment How does software raise exposure in post-processing?
@Octopus There are no separate channels in RAW sensor data. What you get from the sensor looks like the 2nd picture here. In a RAW converter exposure compensation would be applied before demosaicing, using a formula similar to yours. As I said, your formula is simply incorrect if you apply it to RGB values. It's only correct for (linear) raw data coming form the sensor.
Sep
4
comment How much does a camera move in 1/250 of a second?
The shutter speed needed to avoid motion blur will depend on the focal length of the lens. With a telephoto lens even a slight movement translated to very visible shake in the viewfinder. The guideline I've seen most frequently is to use a shutter speed 1/2f with a lens of focal length f. Thus with a 30mm lens 1/60 s should be rather safe to use.
Sep
4
comment Portable tripod recommendations for those on a budget
@dpollitt I managed to borrow a Benro A0690T today (~$150), I'll try it during the week to get an idea about what compromises I'd be making with this model exactly.
Sep
4
comment Portable tripod recommendations for those on a budget
@DanWolfgang It still seems like most vocal people here are simply not interested in cheap tripods, as they consider them equally bad. That's okay, but I find it unfair to close the question just because of that. There are quite a few options below $100, and many below $150. I'm sure they're not made equally so for those who can't afford sums matching a U.S. salary the discussion is not at all irrelevant.
Sep
2
comment Portable tripod recommendations for those on a budget
@dpollitt ... this particular cheap tripod and it has these particular faults which prompted me to get a better one". All I see is people echoing that "you need to spend more" on just about every topic, to the point where someone asking advice about his first camera is suggested to spend several thousand USD because he mentioned "weddings and picnics". My past experience with other items makes me very skeptical about these opinions. What I'm looking for is opinions and experiences from people who have actually tried to use such a budget tripod.