function?y?=?im2jpeg（x?quality）?
%IM2JPEG?Compresses?an?image?using?a?JPEG?approximation.
%???Y?=?IM2JPEG（X?QUALITY）?compresses?image?X?based?on?8?x?8?DCT
%???transforms?coefficient?quantization?and?Huffman?symbol
%???coding.?Input?QUALITY?determines?the?amount?of?information?that
%???is?lost?and?compression?achieved.??Y?is?an?encoding?structure
%???containing?fields:?
%
%??????Y.size??????Size?of?X
%??????Y.numblocks?Number?of?8-by-8?encoded?blocks
%??????Y.quality???Quality?factor?（as?percent）
%??????Y.huffman???Huffman?encoding?structure?as?returned?by
%??????????????????MAT2HUFF
%
%???See?also?JPEG2IM.

%???Copyright?2002-2006?R.?C.?Gonzalez?R.?E.?Woods?&?S.?L.?Eddins
%???Digital?Image?Processing?Using?MATLAB?Prentice-Hall?2004
%???$Revision:?1.5?$??$Date:?2006/07/15?20:44:34?$
%
%???Revised:?3/20/06?by?R.Woods?to?correct?an?‘eob‘?coding?problem?to
%???check?the?‘quality‘?input?for?<=?0?and?to?fix?a?warning?when
%???struct?y?is?created.

error（nargchk（1?2?nargin））;?????????????%?Check?input?arguments
if?ndims（x）?~=?2?|?~isreal（x）?|?~isnumeric（x）?|?~isa（x?‘uint8‘）
???error（‘The?input?must?be?a?UINT8?image.‘）;??
end
if?nargin?==2?&&?quality?<=?0
???error（‘Input?parameter?QUALITY?must?be?greater?than?zero.‘）;
end
if?nargin????quality?=?1;???%?Default?value?for?quality.
end???????

m?=?[16?11??10??16??24??40??51??61????????%?JPEG?normalizing?array
?????12??12??14??19??26??58??60??55???????%?and?zig-zag?redordering
?????14??13??16??24??40??57??69??56???????%?pattern.
?????14??17??22??29??51??87??80??62
?????18??22??37??56??68??109?103?77
?????24??35??55??64??81??104?113?92
?????49??64??78??87??103?121?120?101
?????72??92??95??98??112?100?103?99]?*?quality;

order?=?[1?9??2??3??10?17?25?18?11?4??5??12?19?26?33??...
????????41?34?27?20?13?6??7??14?21?28?35?42?49?57?50??...
????????43?36?29?22?15?8??16?23?30?37?44?51?58?59?52??...
????????45?38?31?24?32?39?46?53?60?61?54?47?40?48?55??...
????????62?63?56?64];

[xm?xn]?=?size（x）;????????????????%?Get?input?size.
x?=?double（x）?-?128;???????????????%?Level?shift?input
t?=?dctmtx（8）;?????????????????????%?Compute?8?x?8?DCT?matrix

%?Compute?DCTs?of?8x8?blocks?and?quantize?the?coefficients.
y?=?blkproc（x?[8?8]?‘P1?*?x?*?P2‘?t?t‘）;
y?=?blkproc（y?[8?8]?‘round（x?./?P1）‘?m）;

y?=?im2col（y?[8?8]?‘distinct‘）;??%?Break?8x8?blocks?into?columns
xb?=?size（y?2）;???????????????????%?Get?number?of?blocks
y?=?y（order?:）;???????????????????%?Reorder?column?elements

eob?=?max（y（:））?+?1;???????????????%?Create?end-of-block?symbol
r?=?zeros（numel（y）?+?size（y?2）?1）;
count?=?0;
for?j?=?1:xb???????????????????????%?Process?1?block?（col）?at?a?time
???i?=?max（find（y（:?j）））;?????????%?Find?last?non-zero?element
???if?isempty（i）???????????????????%?No?nonzero?block?values
??????i?=?0;
???end
???p?=?count?+?1;
???q?=?p?+?i;
???r（p:q）?=?[y（1:i?j）;?eob];??????%?Truncate?trailing?0‘s?add?EOB
???count?=?count?+?i?+?1;?????

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----
?????目錄???????????0??2007-12-04?12:46??jpeg\
?????文件????????3259??2006-07-15?17:06??jpeg\im2jpeg.m
?????文件????????2472??2006-07-15?17:06??jpeg\jpeg2im.m
?????文件????????2817??2006-07-15?17:06??jpeg\mat2huff.m