[fpc-pascal] Why is FPImage dog slow in reading jpeg's?

[Tomas Hajny]

On Mon, May 30, 2011 16:16, michael.vancanneyt at wisa.be wrote:
>
> Try the following code:
>
> Img:=TFPMemoryImage.Create(0,0);
> Img.UsePalette:=False;
> Img.loadFromFile(FileList[i]);
>
> That should work much faster. The reason is probably that the default
> image
> created by the reader uses a palette, which is of course dog slow when
> reading
> large images.

Interesting. What is supposed to be a "large image"? I ask because the
original post mentioned 35 kB and 65 kB (and indirectly also dimensions
around 600x400 if I understand the program output correctly) which I
certainly wouldn't consider as "large" (and the mentioned time necessary
for reading it surely not appropriate regardless of using palette or not).
I guess that some optimization may be reasonable because such pictures
could be loaded and displayed (including conversion from true colour to
256 colours palette) faster even on a 486 machine...

Tomas


>
> On Mon, 30 May 2011, Ben Smith wrote:
>
>> Hi,
>>
>> I wrote this console utility app in 5 minutes. All it is supposed to
>> do, is iterate over *.jpg images (65 at the moment) in a folder (no
>> recursive searches), and generate a snipped of HTML that I need to
>> paste into my wives website.
>>
>> I first thought my utility app is in some recursive loop or something
>> because the output didn't appear instantly - like I thought it would.
>>
>> I added some debug output between the generate HTML. To my surprise
>> the FPImage code reading a 35Kb jpg file takes +- 8 seconds and a 65KB
>> file takes +- 30 seconds - on a Quad Core machine! WTF???
>>
>> Is this normal? Is FPImage really that slow reading small roughly
>> 650x450 pixel jpg images?  Or am I doing something unbelievably
>> stupid? :-/
>>
>> The reason I'm reading in the jpg files is so I can get their Width
>> and Height values. Avg. jpeg file sizes are between 35-45KB, and
>> largest file size is 65KB.
>>
>> Here is the relevant code snippet....
>>
>> var
>>  imgreader: TFPReaderJPEG;
>>  stream: TFileStream;
>>  img:TFPCustomImage;
>>
>> ....
>>
>>  writeln('processing file: ', filelist[i]);
>>  stream := TFileStream.Create(filelist[i], fmOpenRead);
>>  writeln(1);
>>  imgreader := TFPReaderJPEG.Create;
>>  writeln(2, FormatDateTime(' hh:mm:ss.zz', Now) + '  (start reading)');
>>  img := imgreader.ImageRead(stream, nil);
>>  writeln(3, FormatDateTime(' hh:mm:ss.zz', Now) + '  (done)');
>>
>>
>>
>>
>> Here is the program output... Note the timestamps between start
>> reading and done reading (lines marked with '2' and '3').
>>
>>
>> -------------------[ start ]---------------------------
>> $ ./project1 img/babies/full
>> Finished search. Found 65 matches
>> ---------------------------------------
>> <div id="thumbnails">
>> <table cellspacing="10">
>> <tr align="center" valign="middel">	<!--  Row starts  -->
>> <td>
>> processing file: img/babies/full/babies.01.jpg
>> 1
>> 2 16:00:30.210  (start reading)
>> 3 16:00:38.338  (done)
>> <img src="img/babies/full/babies.01.jpg" alt="" id="screen1"
>> class="imglarge" onmouseout="reducethumb(1); return false;"
>> onclick="reducethumb(1); return false;">
>> <img src="img/babies/thumbs/babies.01.jpg" alt="" class="imgsmall"
>> id="thumb1" onclick="expandthumb(1, 650, 413);">
>> </td>
>> </tr>
>> <tr align="center" valign="middel">	<!--  Row starts  -->
>> <td>
>> processing file: img/babies/full/babies.02.jpg
>> 1
>> 2 16:00:38.338  (start reading)
>> 3 16:01:10.447  (done)
>> <img src="img/babies/full/babies.02.jpg" alt="" id="screen2"
>> class="imglarge" onmouseout="reducethumb(2); return false;"
>> onclick="reducethumb(2); return false;">
>> <img src="img/babies/thumbs/babies.02.jpg" alt="" class="imgsmall"
>> id="thumb2" onclick="expandthumb(2, 650, 435);">
>> </td>
>> </tr>
>> <tr align="center" valign="middel">	<!--  Row starts  -->
>> <td>
>> processing file: img/babies/full/babies.03.jpg
>> 1
>> 2 16:01:10.447  (start reading)
>> 3 16:01:28.859  (done)
>> <img src="img/babies/full/babies.03.jpg" alt="" id="screen3"
>> class="imglarge" onmouseout="reducethumb(3); return false;"
>> onclick="reducethumb(3); return false;">
>> <img src="img/babies/thumbs/babies.03.jpg" alt="" class="imgsmall"
>> id="thumb3" onclick="expandthumb(3, 405, 650);">
>> </td>
>> </tr>
>> <tr align="center" valign="middel">	<!--  Row starts  -->
>> <td>
>> processing file: img/babies/full/babies.04.jpg
>> 1
>> 2 16:01:28.859  (start reading)
>>
>> ....snip....
>> -------------------[ end ]---------------------------