For anyone just starting with digital images, or having trouble getting started, here is an review of the first basics we need, about how to USE our digital images, about how to resize them for viewing them on the video screen or for printing. This is about those first basics of resizing images (i.e., the necessary steps to be able to USE and show your images). These methods apply to digital camera images, and scanned photos or documents, any digital image.
This is about the Least that we need to know about using images
ReSample 1.1.5 Free Download for Mac - An intuitive audio editor. An user-friendly audio editor featuring waveform display and numerous software tools for altering the song, along with other other recording options and a built-in equalizer. Much better to provide audio editor,ReSample,audio editor for Mac,ReSample for Mac,ReSample Download, ReSample Free Download, ReSample Full version Download. Scipy.signal.resample¶ scipy.signal.resample (x, num, t = None, axis = 0, window = None, domain = 'time') source ¶ Resample x to num samples using Fourier method along the given axis. The resampled signal starts at the same value as x but is sampled with a spacing of len(x) / num. (spacing of x). Because a Fourier method is used, the.
Why might you want to know? There is good reason:
The problem if Printing: So, you took some important pictures with your digital camera, and you will send them to Walmart or CVS or wherever to be printed, say some 5x7 inch size and a few 8x10 inch size. How do you prepare that? If you do nothing except simply just send them in, they will print them at specified size you ordered, but humans won’t see them first. Meaning, their printing machine can handle resampling the SIZE, but if they are not the same SHAPE as the paper (and they won’t be), then there will be some cut off areas that won’t fit on the paper shape. This could mean cut-off heads and not centered and such. Not the best results. The machine can’t look, and doesn’t care. The print sizes 4x6, 5x7, 8x10 inches are three different shapes. DSLR cameras are 3:2 aspect which at least does match 4x6 paper shape, but the compact and phone cameras are 4:3 aspect which doesn’t match anything. Camcorders vary, but their stills might be 16:9 or 4:3 shape. The odds are “few to none” that any picture can ignore needing this close attention (and the printing machines can’t look and don’t care).
The solution is that some human (meaning you, to be your choice) first processes each image to prepare it for printing, cropping its shape to match the desired paper shape (centering the scene as you choose) for the best fitting the important scene area into that cropped result. This is really easy to do, maybe only several seconds each after you get the hang of it, but it takes a human who cares about best result. Instead of cutting into the subject, you simply crop away the uninteresting or distracting or blank wasted areas, giving due importance to the desired subject area, also with the result matching the intended paper shape. Details about how are on the next page here, but basically you choose a Crop Tool box the shape of the paper (say 4x6, 5x7 or 8x10, or maybe width x height is 6x4, 7x5, or 10x8 for landscape orientation), and then simply mark that crop box on the image with the mouse, and position and size it as seen to be the best view result that you prefer. This box can change Size as desired, but this tool remains the same Shape (but there is a similar option that does NOT remain the same shape). Then you are expected to say “Wow, that was easy”, and this will be even easier and faster to do the second time you see it. And the print will come out just as you marked it.
One caution: Do NOT overwrite your original file, which would interfere with later future plans. The SAVE operation should specify a different file name. If you will print it on two sizes of paper, you should prepare two appropriate crops (each from the original), and label the final file name as which shape it is so you will know when selecting them to be printed. Otherwise, the printing machine will simply crop them as necessary to fit the paper shape.
This much is all that is actually required to prevent bad cropping results. If necessary, the print shop will resample it to the smaller size required to print, but you may be uploading huge 16 or 24 megapixel images when you only need about 2 megapixels for best 4x6, or about 3 megapixels for 5x7 prints, or 7 megapixels for 8x10. It does need to be large enough (about 250 to 300 pixels of size per inch of print), but too large is simply a waste. It is trivially easy for you to resample them to appropriate size yourself while you’re at it. I’d add that as a desirable plan (this resampling is also on the next page).
![Resample 1 1 5 equals Resample 1 1 5 equals](https://www.mathworks.com/help/examples/signal/win64/ResamplingALinearSequenceExample_02.png)
Or if planning a slide show on a HDTV television set: First, there are no inches or cm defined in video images. Video images show on any size screen, which are also dimensioned in pixels. HDTV screens are 1920x1080 pixels or 1280x720 pixels. That is the image size, and the shape is Aspect 16:9, which is 1.778 times wider than tall. If you don’t know about the TV that will show them, you could just plan on either size and all will be fine (some TV channels send one size, others send the other size). But 1920x1080 will be optimum for all cases. But if you try to show the original huge images, it will seriously slow the TV loading each one. And if not 16:9 shape, they won’t fit the screen shape, so there will be black bands at both sides. The black bands are maybe not so serious for video, except they cause showing a smaller picture than you could show if you cropped the shape to 16:9 for the HDTV showing. If the images will be shown more than once, for guests other than yourself, a little preparation is certainly worthwhile. Images vary, some include wasted space easily cropped to 16:9, but some are already filled tightly, so that 16:9 just won’t work for them, and black side bands may be better for some. So there are choices to be made. But again, the situation is the same as the printing above — with different numbers, but which is to crop to TV shape (16:9) and then resample to TV size (1920x1080 is about 2 megapixels, or 1280x720 is about 1 megapixel).
Again, a very good plan is to Never overwrite your original camera file. This work just mentioned will be awesome for your current plan, but the future could have different plans for the image, unknown now. I’d suggest only making copies, and Never overwriting your original camera file. They are not too big to store some archived place. Maybe on a CD or DVD disc in a desk drawer.
So that is what this article is about, how to do that easily and correctly. Which is how to first crop to shape, and then resample to size, for viewing or printing. In truth (at least for me), our pictures didn’t always frame the scene the best way, so a little additional tighter cropping improves most pictures anyway (getting rid of distracting areas, and excess nothingness wasting space at the edges). Kodak’s Better Photo Tips always said “Get close to your subject”, and cropping is one way, especially when reducing Size for printing or video. And for most of us, this is a fun part of the photography hobby; the creation ain’t done until it is your best result. This actual instruction is on the next page, but first, some more reasons and background are shown here. Knowing why tells you how.
4.1 Basics
4.1.1 What is “resampling”?
“Resampling” means combining interpolation and decimation to change the sampling rate by a rational factor.
4.1.2 Why resample?
Resampling is usually done to interface two systems which have different sampling rates. If the ratio of two system’s rates happens to be an integer, decimation or interpolation can be used to change the sampling rate (depending on whether the rate is being decreased or increased); otherwise, interpolation and decimation must be used together to change the rate
A practical and well-known example results from the fact that professional audio equipment uses a sampling rate of 48 kHz, but consumer audio equipment uses a rate of 44.1 kHz. Therefore, to transfer music from a professional recording to a CD, the sampling rate must be changed by a factor of:
(44100 / 48000) = (441 / 480) = (147 / 160)
There are no common factors in 147 and 160, so we must stop factoring at that point. Therefore, in this example, we would interpolate by a factor of 147 then decimate by a factor of 160.
4.1.3 What is the “resampling factor”?
The interpolation factor is simply the ratio of the output rate to the input rate. Given that the interpolation factor is L and the decimation factor is M, the resampling factor is L / M. In the above example, the resampling factor is 147 / 160 = 0.91875
4.1.4 Is there a restriction on the resampling factor I can use?
Yes. As always, the Nyquist criteria must be met relative to the resulting output sampling rate, or aliasing will result. In other words, the output rate cannot be less than twice the highest frequency (of interest) of the input signal.
4.1.5 When resampling, do I always need to a filter?
Yes. Since resampling includes interpolation, you need an interpolation filter. Otherwise, the images created by the zero-stuffing part of interpolation will remain, and the interpolated signal will not be “the same” as the original.
Likewise, since resampling includes decimation, you seemingly need a decimation filter. Or do you? Since the interpolation filter is in-line with the decimation filter, you could just combine the two filters by convolving their coefficients into a single filter to use for decimation. Better yet, since both are lowpass filters, just use whichever filter has the lowest cutoff frequency as the interpolation filter.
4.1.6 How do I design the resampling filter?
![Resample Resample](https://i0.wp.com/www.real-statistics.com/wp-content/uploads/2015/01/bootstrapping-correlation-coefficient.png?resize=640%2C293)
As hinted at above:
- Determine the cutoff frequency of the decimation filter (as explained in Part 2: Decimation.)
- Determine the cutoff frequency of the interpolation filter (as explained in Part 3: Interpolation)
- Use the lower of the two cutoff frequencies to design the resampling filter.
4.2 Multistage
4.2.1 Can I resample in multiple stages?
Yes, but there are a couple of restrictions:
- If either the interpolation or decimation factors are prime numbers, you won’t be able to decompose those parts of the resampler into stages.
- You must preserve the Nyquist criteria at each stage or else aliasing will result. That is, no stage can have an output rate which is less than twice the highest frequency of interest.
4.2.2 Cool. But why bother with all that?
Just as with interpolation and decimation, the computational and/or memory requirements of the resampling filtering can sometimes be greatly reduced by using multiple stages.
4.3 Implementation
4.3.1 How do I implement resampling?
The straight-forward implementation of resampling is to do interpolation by a factor of L, then decimation by a factor of M. (You must do it in that order; otherwise, the decimator would remove part of the desired signal–which the interpolator could not restore.)
4.3.2 Is that straight-forward implementation efficient?
No. The problem is that for resampling factors close to 1.0, the interpolation factor can be quite large. For example, in the case described above of changing from the sampling rate from 48 kHz to 44.1 kHz, the ratio is only 0.91875, yet the interpolation factor is 147!
Also, you are filtering the signal twice: once in the interpolator and once in the decimator. However, one of the filters has a larger bandwidth than the other, so the larger-bandwidth filter is redundant.
4.3.3 So what’s the cure?
Just combine the computational and memory advantages that FIR interpolator and decimator implementations can provide. (If you don’t already understand those, be sure to read and understand Part 2: Decimation, and Part 3: Interpolation before continuing.)
First, let’s briefly review what makes FIR interpolation and decimation efficient:
Resample 1 1 5 Fraction
- When interpolating by a factor of L, you only have to actually calculate 1/L of the FIR taps per interpolator output.
- When decimating by a factor of M, you only have to calculate one output for every M decimator inputs.
So, combining these ideas, we will calculate only the outputs we actually need, using only a subset of the interpolation coefficients to calculate each output. That makes it possible to efficiently implement even FIR resamplers which have large interpolation and/or decimation factors.
The tricky part is figuring out which polyphase filters to apply to which inputs, to calculate the desired outputs, as a function of L and M. There are various ways of doing that, but they’re all beyond our scope here.
Resample 1 1 5 X 2
4.3.4 Where can I get source code to implement a FIR decimator in C?
Iowegian’s ScopeFIR comes with a free set of multirate algorithms, including FIR resampling functions in C. Just download and install the ScopeFIR distribution file.
Resample 1 1 5 0
4.3.5 How do I test a FIR resampler?
Resample 1 1 5 Equals
- The most obvious method is to put in a sine whose frequency is within the resampler’s passband. If an undistorted sine comes out, that’s a good sign. Note, however, that there will typically be a “ramp up” at the beginning of the sine, due to the filter’s delay line filling with samples. Therefore, if you analyze the spectral content of the sine, be sure to skip past the ramp-up portion.
- Depending on the resampling factor, resampling can be thought of as a general case of other types of multirate filtering. It can be:
- Interpolation: The interpolation factor, L, is greater than one, and the decimation factor, M, is one.
- Decimation: The interpolation factor, L, is one, but the decimation factor, M, is greater than one.
- “Ordinary” Filtering: The interpolation and decimation factors, L and M, are both one.
Therefore, if you successfully test it with all these cases using the methods appropriate for each case, it probably is correct.