What is Compression: Definition and 632 Discussions

Lossless compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data. By contrast, lossy compression permits reconstruction only of an approximation of the original data, though usually with greatly improved compression rates (and therefore reduced media sizes).
By operation of the pigeonhole principle, no lossless compression algorithm can efficiently compress all possible data. For this reason, many different algorithms exist that are designed either with a specific type of input data in mind or with specific assumptions about what kinds of redundancy the uncompressed data are likely to contain.
Lossless data compression is used in many applications. For example, it is used in the ZIP file format and in the GNU tool gzip. It is also often used as a component within lossy data compression technologies (e.g. lossless mid/side joint stereo preprocessing by MP3 encoders and other lossy audio encoders).
Lossless compression is used in cases where it is important that the original and the decompressed data be identical, or where deviations from the original data would be unfavourable. Typical examples are executable programs, text documents, and source code. Some image file formats, like PNG or GIF, use only lossless compression, while others like TIFF and MNG may use either lossless or lossy methods. Lossless audio formats are most often used for archiving or production purposes, while smaller lossy audio files are typically used on portable players and in other cases where storage space is limited or exact replication of the audio is unnecessary.

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  1. Superposed_Cat

    Image Compression you can implement in a day

    I need to implement a decent image compression algorithm in a day or two, without using libraries. So it can't be anything with multiple layers, like jpeg. I was thinking huffman encoding, Which would be a good algorithm I can learn to implement in a day or two that is not terrible at it's job.
  2. DennisN

    Bug Image degradation (compression?) in copied threads

    Hi! I recently noticed that posted images can lose quality when they are copied from a thread to a new thread. It seems they undergo some extra compression, and I don't understand why. Compare for instance the photos in this PF photo contest thread with the photos in the corresponding vote...
  3. MatNX

    What would happen if a Pokéball expelled 999.8kgs of air in 1 second?

    If we were to suppose the pokéball gets rid of the pokémons mass by expelling it as air, what would happen? Imagine we had a pokémon weighing 999.9kgs, being a perfect sphere and having a diameter of 10cms. (Cosmovum). If the Pokéball takes 1 sec to capture or to release a pokémon, and it...
  4. W

    Buffering and delay in video compression

    1) What is the relationship between buffer at encoder and buffer at decoder? 2) How much preloading is necessary to ensure no buffer empties over the length of the simulation I.e. what is the minimum no. of bytes that must be in the buffer? 3)How to estimate delay due to buffering? 4) What is...
  5. C

    Could somebody please explain the vapor compression cycle?

    Heat is taken from food in the refrigerated space to the evaporator which has evaporated (I am assuming saturated vapor) refrigerant flowing through it. My first stumble would be, if this is true, why doesn't the temperature increase for the fluid coming out of the evaporator (unless it is...
  6. LordGfcd

    Compression of an object under it's own weight.

    Let's first consider a cube side length a, mass m, Young's modulus of the block is E. How do we calculate the decrease of the height of the center of mass of that cube ?
  7. M

    Can Infinite Data Compression Potentially Create a Black Hole?

    I am fascinated with data compression, and for the past 7 years i have been trying to create an algorithm that can compress information almost infinitely let's say for example 1GB of information into 1KB of information, and while impossible that sounds after 7 years working at that problem 16...
  8. W

    Capture and re-use the heat generated from Air Compression

    I am trying to fill pipes with a volume of 556 cuft to 15,000 psi. I want to capture and re-use the heat generated from the compression process and re-use it. Is this amount of compression and heat exchanging possible with current technology
  9. J

    Design a non-linear conical compression spring

    What is the method to design a Non - Telescopic, Non - Linear, conical compression spring from a Force - Deflection characteristics
  10. beefbrisket

    Assumed value of pressure during quasistatic compression

    My text (Ian Ford - Statistical physics) describes an ideal gas system in a piston being quasistatically compressed by a piston head of area A under external force f. It assumes the system has a uniform pressure p. All good so far. Then it says: "the force pA equals the applied external force f"...
  11. Another

    Thermodynamics: adiabatic compression

    Homework Statement Question If changed isothermal compression process to adiabatic compression process. find the final temperature of process. Homework Equations ## \alpha = \frac{1}{v} (\frac{∂v}{∂T})_{P} ## expansivity ## \beta = -\frac{1}{v} (\frac{∂v}{∂P})_{T} ## compressibility...
  12. H

    Calculate Force Compression of Crane with Hoisting Slink

    Actually it is a simple one, but the point of view of the force acting in pic attach of some people are different. http://www.imagebam.com/image/ef24231032403754 http://www.imagebam.com/image/01c8e71032403724 The adding weight of hoisting slink blue and the pulley is neglected. I think the...
  13. hawkeye1029

    Compression of a spring by an object in free fall

    Homework Statement A 2.0 kg object starting at rest falls 3.0 m onto a 4.0 N/m spring. How far will the spring be compressed? m = 2.0 kg vo = 0 m/s2 y = 3 m k = 4 N/m g = -9/8 m/s2 Homework Equations eq1: Fg = mg eq2: Fspring = -kx The Attempt at a Solution [/B] eq1: Fg = mg Fg =...
  14. maxd23

    Compression of human bone: forces

    Homework Statement While unrealistic, we will examine the forces on a leg when one falls from a height by approximating the leg as a uniform cylinder of bone with a diameter of 2.3 cm and ignoring any shear forces. Human bone can be compressed with approximately 1.7 × 10^8 N/m2 before...
  15. Dave Mata

    Adiabatic Reversible Compression of a Solid

    Homework Statement Derive an expression for the change of temperature of a solid material that is compressed adiabatically and reversible in terms of physical quantities. (The second part of this problem is: The pressure on a block of iron is increased by 1000 atm adiabatically and...
  16. S

    I Compression of gases that liquefies

    For example we had a closed system with water at 298K, so it's pressure is 0.031atm. To it we add a gas, A such that we get 1atm of total pressure. That gas undergoes a phase transition at 1.5atm and 298K. So initially, the partial pressure of water is a little smaller than 0.031atm due to the...
  17. K

    I Reversible compression of a gas - faulty reasoning?

    Hello, I am trying to figure out where my reasoning falls apart in this thought experiment: To determine if a process "A" is reversible (or at the very least internally reversible), I try to picture a reversible process "B" that involves only heat transfer and links the same two endpoints that...
  18. S

    Plumbing Do pipe fittings work with male compression fittings?

    Does an ordinary pipe fitting, such as an elbow work when screwed onto a male compression fitting"? - or won't the connection seal properly? The situation shown in the photo: I need to replace a 1/4 inch copper tube water supply line (to the ice maker on a refrigerator) with a 1/4 inch braided...
  19. SirMarx01

    Automotive What is the compression force of a ring seated inside a cylinder

    Hello. I am finding out how many normal force between ring and cylinder. I try to find around for many hours but get noting. there are 8.2 mm inner diameters than put in 8.6 mm cylinder. The hardness of sealing element is 55 ShA. Contact area is 48.63 mm^2. I have data and drawing in attachment...
  20. jacobthejones

    Statics - Compression and tension forces in a truss

    Homework Statement I am trying to find the forces in KJ, CJ, and CD. Homework Equations ΣFx=0 The Attempt at a Solution I found the magnitude of KJ to be 26.8kN, which is correct (according to answers in the back of the book). I believe it is a compressive force. The book lists all 3 forces...
  21. BransonMO

    Effect of zero gravity on spinal compression

    I am trying to compare an experiment on spinal changes due to zero-g in astronauts. Researchers simulated zero-g spinal elongation by suspending human subjects so that no part of their body touched the ground. This figure shows the % change in disc thickness for each subject compared to data...
  22. B

    Data compression with lissajous curve

    I was hoping this c++ file could be adapted to use as data compression or encryption #include <iostream> #include <cmath> using namespace std; double asil(double t) { cout<<"asil\n"; cout<< cos(t) << endl; double two = 2.0; cout<< sin(sqrt(two)*t) << endl; return sin(sqrt(two)*t); } int...
  23. M

    Isothermic and adiabatic compression

    Homework Statement Determine the ratio of the work that you must expend when a single-atom ideal Gas once isothermic and once adiabatic to 1/10 of its original volume is compressed. In both cases the initial pressure, initial volume and gas amount are all equal. The Attempt at a Solution Case...
  24. isukatphysics69

    Find the max compression of the spring

    Homework Statement Homework Equations ke = .5mv^2 The Attempt at a Solution Ei= .5m1v21 + .5m2v22 + PEs(PEs initially 0) Ef= .5m1v21 + .5m2v22 + PEs(PEs is now .5(16.2)(.2672)set them equal and then solve for velocity right? is this the right approach?
  25. bravopipo

    Calculate the characteristics of this compression spring

    Homework Statement Hello; I have as shown in the picture, a rope (in green), this rope is located between a support A and a support B. The Support A doesn't move and attached to the ground. The support B apply a force F1 against the rope, this force is made by a helical compression spring...
  26. Philip Koeck

    The exact formula for PV-work in an irreversible process

    I've written a short text adapted from a previous post by Count Iblis. I'll append it below. It shows that irreversible PV-work is always smaller than reversible, which fits very nicely with W = Pext ΔV. I'd be interested if there's a way to show that W is exactly equal to Pext ΔV for all...
  27. B

    Compression and Expansion of a Volume of Air

    Homework Statement Air with an initial volume of 0.12m³, pressure 1 bar and temperature 18°C is compressed according to the law pV1.3 = c through an 8:1 compression ratio. It is then allowed to expand isothermally back to its initial volume. Determine: i) the pressure and temperature after...
  28. Cianturyo

    How to calculate changes in the radius of a surface under compression?

    How do i calculate percentage of changes in radius, when the surface which cause the radius, will be compressed by a certain percentage? To illustrate better, i have drawn the picture of the question. How to calculate radius ?? if radius A Is known. Changes in the surface is also known. Thank...
  29. B

    I Hydrogen plasma compression with liquid Mercury piston

    I'm working on a thought experiment. I want to know how much of the kinetic energy from a liquid mercury piston will be converted into work done on the hydrogen plasma in the form of compression, and how much work will be done on the piston in the form of compression. Note: assume piston walls...
  30. E

    How Much Does the Spring Compress When a Man Jumps on a Scale?

    Homework Statement As a 75.0 kg man steps onto a scale, the spring inside the scale compresses by 0.65 mm. Excited to see that he has lost 2.5 kg since his last weighing, he jumps 0.3 m straight up into the air and lands directly on the scale. What is the spring’s maximum compression? What...
  31. T

    Quadratic equation for maximum compression of a spring

    Homework Statement A 1.2 kg block is dropped from a height of 0.5 m above an uncompressed spring. The spring has a spring constant k = 160 N/m and negligible mass. The block strikes the top end of the spring and sticks to it Find the compression of the spring when the speed of the block...
  32. M

    B Elements capable of cooling without compression?

    Wondering if anybody had information on cooling elements such as coils or plastics?
  33. Q

    Inverse bulk modulus / compression or shear?

    Hi, I'm afraid I not very good at these questions just yet and would like a walk through a bit better than the one I was given by my tutors. Thank you, please refer to the inline image.
  34. D

    Resources for air flow/air compression physics

    I am attempting to identify how long it would take to bring different volumes to a specific pressure using air compressors. I understand that the flow rate given for an air compressor will change as the outlet pressure increases, but I am having some trouble finding the equations to describe...
  35. A

    Automotive Air compression firing mechanism

    Hello, I am high school student working on a project to design an air cylinder, which would fire seed pellets from the drone at specific time intervals with sufficient pressure to embed them into the soft soil. I looked up on the Internet about airguns and other stuff but couldn't find...
  36. R

    Reversible work of compression

    Homework Statement Air enters a compressor at 100 [Kpa] and 10 [c], the air leave the compressor at 12[Mpa] the isentropic efficiency η is 87%, calculate: work done reversible work irreversibility Homework Equations [/B] T2=T1(P2/P1)(1.4-1)/1.4 W = (Cp(T2-T1))/η Wrev=Δh - T0Δs Δs =...
  37. V

    Initial compression of a spring

    My question here is a simple one. Most tension springs come with an initial tension requirement for spring action. Is it that tension springs are usually used for measuring through some range while compression springs are usually energy absorbers that such a difference is built into them? Also...
  38. B

    Compressing Gas: Work Done Calculation

    Homework Statement [/B] A closed cylinder with a piston is used to compress gas that is initially at 1bar and temperature 293K. The compression is performed adiabatically until the volume is 1m3 and the pressure is 10bar, calculate the work done. Homework Equations [/B] pV = nR0T - ideal gas...
  39. kq6up

    Time to Max Compression of a Spring

    Homework Statement [/B] A block of mass m slides down an incline with a height h. Later, it collides with a spring and compresses the spring to some maximum displacement. How long does it take to reach maximal compression.Homework Equations [/B] 1) ##mgh=\frac{1}{2}mv^2+\frac{1}{2}kx^2## 2)...
  40. H

    Height of falling object vs. compression of spring

    1. Question Given an idea spring with constant K, a mass of M is dropped onto the spring from a height of H1. The spring compresses D distance. We take the mass off, and drop the mass again at a height of H2, where H2 is significantly greater than H1. This time, will the spring compress a...
  41. Deadawake

    Bullet & Spring compression

    Hi, Please see the attach picture. I solved 3 quetions regarding this problem and I struggle with the 4th one. What I found was that the initial velocity after the collision is 1.98 m/s (Edit: 0.2m/s), and the maximum compression of the spring with no friction beneath is 0.44m (Edit: 0.044m) (I...
  42. olgkd123

    How does compression cool water in a household water cooler?

    How does compression cool water in a household water cooler? I was reading and it says, " The water inside the water cooler is fed into a reservoir, where it is cooled using a refrigerant. A refrigerant is a cooling medium that is circulated in pipes that are located close to the reservoir in...
  43. Atom

    Determine the highest tension stress and the highest compression stress

    Homework Statement Determine the highest tension stress and the highest compression stress along the top edge of the intel. Homework Equations stressx = Mx*y / Ix Ztop = Ix / ytop stress (max top) = Mx - Ztop The Attempt at a Solution
  44. R

    How does pressure ratio and intercooling affect gas turbine performance?

    Hey Mech Eng Forum, I'm currently examining the performance on gas turbine and wondering: How is the performance of gas turbines (Primarily thermal efficiency and net-work output) influenced by the pressure ratio and temperature constraints? Additionally, what is the benefit of 2 stage...
  45. M

    Mechanical expansion or compression of a material

    Would you explain what "mechanical expansion or compression of a material" is? It makes no sense to me I only know thermal expansion or compression. https://www.google.tl/patents/US5004946 Thank you.
  46. G

    Calculation of heat created during compression

    Homework Statement Hello, I have a task to make a heat balance of the evaporator. To do this, I was told to carry a few smaller energy balances in different parts of the evaporator. One of the things I had to calculate was the heat generated during steam compression. -steam is entering...
  47. A

    Compression/Tension in Steel I Beams

    Homework Statement Why is a steel beam shaped in the form of the letter "I" still strong enough to bear a load? 1) Its compression area is located on the top of the I beam. 2) Its tension area is located on the top of the I beam. 3) Its neutral area is located on the top of the I beam. 4) Its...
  48. M

    Thermodynamics: Compression of an Adiabatic Gas

    Homework Statement Assume 1.500 mol of a monatomic ideal gas is compressed from 3.00 L to 1.00 L. a. If the initial and final temperature is 10.0 °C, what are the initial and final pressures (in atm)? b. How much work input (in kJ) is required if a reversible isothermal path at 10.0 °C is...
  49. dannyboy2233

    How to analyze the compression of a clay ball

    Hello all! This is my first post on the forum. As some background, this issue pertains to the IB Physics Internal Assessment that I am in the process of writing. Thanks in advance for your help! Homework Statement My research question is: How does the drop height of a consistent-size clay ball...
  50. G

    How to calculate stress on a pipe wall

    I have a PVC fitting that keeps cracking. The fitting consists of 2 parts. One piece is placed over the end of a flexible PVC ribbed hose, and the other is inserted inside the hose. The 2 parts act as a compression fitting to attach to the end of the hose. The hose typically has an outside...
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