我使用x265和libjasper（jasper Jpeg2000）编解码器实现了图片编码软件，我在无损压缩模式下有奇怪的比率压缩。
我的比例压缩是
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
import Data.List
import Debug.Trace (trace)
main = print $ runUniverse makeUniverse 0.1 0.01
newtype Length = Length {unLength::Double}
newtype Mass = Mass {unMass::Double} deriving (Num,Eq,Show)
newtype Charge = Charge {unCharge::Double} deriving (Num,Eq,Show)
newtype Time = Time {unTime::Double} deriving (Num,Eq,Ord,Fractional)
type Vector = (Double,Double,Double)
newtype Position = Position {unPosition::Vector} deriving (Eq,Show)
newtype Velocity = Velocity {unVelocity::Vector} deriving (Eq,Show)
newtype Acceleration = Acceleration {unAcceleration::Vector}
newtype Force = Force {unForce::Vector} deriving (Eq,Show)
data Widget = Widget {pos :: Position, mass :: Mass, charge :: Charge, velocity :: Velocity} deriving (Eq, Show)
--utils
toScalar :: Vector -> Double
toScalar (x, y, z) = sqrt (x ^^ 2 + y ^^ 2 + z ^^ 2)
toUnit :: Vector -> Vector
toUnit (x, y, z) = (x / scalar, y / scalar, z / scalar)
where
scalar = toScalar (x, y, z)
add :: Vector -> Vector -> Vector
add (x1, y1, z1) (x2, y2, z2) = (x1 + x2, y1 + y2, z1 + z2)
mult :: Vector -> Double -> Vector
mult (x, y, z) k = (k * x, k * y, k * z)
diff :: Vector -> Vector -> Vector
diff (x1, y1, z1) (x2, y2, z2) = (x1 - x2, y1 - y2, z1 - z2)
--calcs
gForce :: Widget -> Widget -> Force
gForce (Widget (Position pos1) (Mass mass1) _ _) (Widget (Position pos2) (Mass mass2) _ _) = Force (mult unitForce scalarForce)
where
unitForce = toUnit posdiff
scalarForce = (g * mass1 * mass2) / (radius ^^ 2)
g = 6.674e-11
radius = toScalar posdiff
posdiff = diff pos1 pos2
eForce :: Widget -> Widget -> Force
eForce (Widget (Position pos1) _ (Charge charge1) _) (Widget (Position pos2) _ (Charge charge2) _) = Force (mult unitForce scalarForce)
where
unitForce = (toUnit posdiff)
--necessary to determine attraction vs repulsion, whereas gravitational is always attractive
scalarForce = ((abs (k_C * charge1 * charge2)) / (radius ^^ 2)) * (signum charge1) * (signum charge2)
k_C = 8.988e9
radius = toScalar posdiff
posdiff = diff pos1 pos2
netForce :: [Force] -> Force
netForce = Force . foldl add (0,0,0) . map unForce
toAccel :: Force -> Widget -> Acceleration
toAccel f (Widget _ mass _ _) = Acceleration (mult (unForce f) (unMass mass))
newVeloc :: Velocity -> Acceleration -> Time -> Velocity
newVeloc v a dt = Velocity (add (unVelocity v) (mult (unAcceleration a) (unTime dt)))
newPos :: Position -> Velocity -> Time -> Position
newPos s v dt = Position (add (unPosition s) (mult (unVelocity v) (unTime dt)))
newWidget :: Widget -> Position -> Velocity -> Widget
newWidget w@(Widget pos1 _ _ vel1) dpos dvel = w { pos=Position ((unPosition dpos)),velocity=Velocity ((unVelocity dvel)) }
tUniverse :: [Widget] -> Time -> [Widget]
tUniverse widgets dt = zipWith3 newWidget widgets (trace (show poses) poses) (trace (show vels) vels)
where
netMassForces = map (\w -> gForcePrime w (widgets \\ [w])) widgets
gForcePrime w ws = netForce $ map (gForce w) ws
netElectricForces = map (\w -> eForcePrime w (widgets \\ [w])) widgets
eForcePrime w ws = netForce $ map (eForce w) ws
volds = map velocity widgets
polds = map pos widgets
accels = zipWith toAccel (map netForce (zipWith (\a b -> a : [b]) netMassForces netElectricForces)) widgets
vels = zipWith (\v a -> newVeloc v a dt) volds accels
poses = zipWith (\s v -> newPos s v dt) polds vels
makeUniverse :: [Widget]
makeUniverse = [Widget (Position (1,0,0)) (Mass 0) (Charge 0) (Velocity (1,0,0))] -- , (Widget (1, 0, 0) 9e-31 1 (0, 0, 0))]
runUniverse :: [Widget] -> Time -> Time -> [Widget]
runUniverse ws t dt
| t < 0 = ws
| otherwise = runUniverse (tUniverse (inelasticCollide ws) dt) (t-dt) dt
inelasticCollide :: [Widget] -> [Widget]
inelasticCollide [] = []
inelasticCollide (w:[]) = [w]
inelasticCollide (w:ws) = (combine w (sameposes w ws)) : (inelasticCollide $ ws \\ (sameposes w ws))
where
sameposes w ws = filter (\w' -> pos w == pos w') ws
combine :: Widget -> [Widget] -> Widget
combine = foldl (\(Widget pos mass1 charge1 veloc1) (Widget _ mass2 charge2 veloc2) -> Widget pos (mass1 + mass2) (charge1 + charge2) (Velocity (newveloc (unMass mass1) (unMass mass2) (unVelocity veloc1) (unVelocity veloc2))))
--inelastic collision, m1v1 + m2v2 = m3v3 therefore v3 = (m1v1 + m2v2)/(m1 + m2)
newveloc m1 m2 v1 v2 = ((v1 `mult` m1) `add` (v2 `mult` m2)) `mult` (1 / (m1 + m2))
大多数研究表明hevc优于jpeg2000但在我的情况下，jpeg2000比率优于x265比率。 我也使用jasper软件和x265软件获得相同的结果。
所以我想也许我的x265输入参数不正确......
通常情况下，我正在处理单色图像，8位深度。但是我用彩色图片做了同样的测试，我得到了相同的结果。
此处有彩色图片的相同结果（原始图片）http://mmspg.epfl.ch/iqa
( 1 - output_stream_size / initial_picture_size).Hevc输出跟踪： Hevc encoder output trace
输出文件大小：
原始输入：6144017字节
hevc bitstream：5637967 bytes
jp2比特流：3261791字节
编解码器版本：
x265 --psy-rd 1.0 --lossless --input-res 1280x1600 --input-csp i420 --fps 1 --preset veryslow --profile mainstillpicture bike_orig.yuv bike_orig.bin
jasper -f bike_orig.ppm -F bike_orig.jp2 -T jp2
有没有人知道我为什么会有这样的结果。
谢谢你。
答案 0 :(得分：0)
在考虑无损编码时，JPEG2000压缩比优于HEVC。这主要原因似乎是JPEG2000中discrete wavelet transformation优于discrete cosine transformation的优势。
有关进一步的详细信息，请参阅this。 （评估：HEVC，H.264 / AVC，JPEG 2000和JPEG LS）
编辑：关于静态图片编码，JPEG2000可能更加优越，因为HEVC无法利用帧间视频压缩。
答案 1 :(得分：0)
感谢您的回答。我已经阅读了这篇论文来证明我的结果。但我注意到这篇文章介绍了有关视频（动态图片）的结果。我们可以将其扩展到静态图片。那么我们可以比较Jpeg2000和HEVC MainStill Picture（MSP）吗？