[Mono-winforms-list] Weird issues reading pixels of jpg file on osx

[Sebastien Pouliot]

Hello Dan,

[please c.c. the mailing-list in your answers]

I found a problem with (most) JPEG files where the first two lines had
some bad values. This is fixed in SVN :-)

However my (new) unit tests using LockBits are all failing - even for
bitmaps. Something else is wrong there :-(

Note that I'm still curious to know if this was working on previous Mac
OS X releases ;-)

On Thu, 2006-08-31 at 08:21 -0700, Dan Shryock wrote:
> Hi Sebastien,
> 
> Thanks for looking into this.  I just tried it on a png file instead
> of the jpeg, and I am still seeing different results for the pixel
> data.
> 
> On windows the first few bytes were as follows:
> 196
> 144
> 73
> 195
> 143
> 72
> 
> while on osx they were:
> 255
> 144
> 73
> 255
> 255
> 72
> 
> So something similar seems to be affecting png reading as well as jpeg reading.
> 
> Dan
> 
> On 8/31/06, Sebastien Pouliot <sebastien at ximian.com> wrote:
> > Hello Dan,
> >
> > It may be unrelated to endian issues (but I still like your answers,
> > multiple problems are common ;-) as I also found out differences between
> > Mono on Linux i386 and Windows.
> >
> > It seems, in my test case, that the first two lines of the decoded jpeg
> > aren't correct. In the first line all 2nd and 4th bytes are identical,
> > while on the second line all 3rd and 4th bytes are identical (on the
> > mono side, the 4th byte being correct). All other lines looks correct
> > (but needs more investigation).
> >
> > I'm re-enabling the JpegCodec unit tests (not sure why they were
> > commented, the ChangeLog says "fixed") and adding new test cases.
> >
> > Thanks for noticing this.
> >
> > On Wed, 2006-08-30 at 20:08 -0400, Sebastien Pouliot wrote:
> > > Hello Dan,
> > >
> > > Did the same code worked on a previous version of Mono ? (if so which
> > > version ?) or are you testing this for the first time ?
> > >
> > > Because I recently fixed many endian issues affecting Mac OS X (and
> > > other architectures). It is possible that one of them has broken
> > > something else :-(
> > >
> > > I'll try to build a similar test case using one of the embedded bitmap
> > > files we have in the unit tests and see how to bots reacts to it.
> > >
> > > On Wed, 2006-08-30 at 15:56 -0700, Dan Shryock wrote:
> > > > When attempting to read the pixel bytes of a jpg on osx (using the
> > > > 1.1.17 build just released) I am getting different results on windows
> > > > versus osx.  Does anybody have any ideas why I am getting these
> > > > different results?  Any information is very appreciated.
> > > >
> > > > Dan
> > > >
> > > >
> > > > The code being used is as follows:
> > > >
> > > > Bitmap bmp = new Bitmap("file.jpg");
> > > > BitmapData bmpdata = bmp.LockBits(new Rectangle(0,0,bmp.Width,
> > > > bmp.Height),ImageLockMode.ReadOnly,PixelFormat.Format24bppRgb);
> > > >
> > > > unsafe{
> > > >     byte* scandata = (byte*) bmpdata.Scan0;
> > > >     for(int i=0; i<30; i++){
> > > >             Console.WriteLine(scandata[i]);
> > > >     }
> > > > }
> > > >
> > > >
> > > > and the results using mono on windows are:
> > > > 187
> > > > 144
> > > > 77
> > > > 187
> > > > 144
> > > > 77
> > > > 186
> > > > 144
> > > > 75
> > > > 188
> > > > 143
> > > > 75
> > > > 188
> > > > 144
> > > > 73
> > > > 189
> > > > 145
> > > > 74
> > > > 192
> > > > 147
> > > > 74
> > > > 192
> > > > 147
> > > > 74
> > > > 192
> > > > 150
> > > > 75
> > > > 191
> > > > 149
> > > > 74
> > > >
> > > > while the results on osx are:
> > > > 255
> > > > 255
> > > > 255
> > > > 255
> > > > 255
> > > > 77
> > > > 255
> > > > 255
> > > > 255
> > > > 255
> > > > 77
> > > > 255
> > > > 255
> > > > 255
> > > > 144
> > > > 75
> > > > 255
> > > > 143
> > > > 75
> > > > 255
> > > > 255
> > > > 73
> > > > 255
> > > > 188
> > > > 255
> > > > 255
> > > > 188
> > > > 144
> > > > 255
> > > > 189
> > > > _______________________________________________
> > > > Mono-winforms-list maillist  -  Mono-winforms-list at lists.ximian.com
> > > > http://lists.ximian.com/mailman/listinfo/mono-winforms-list
> > --
> > Sebastien Pouliot  <sebastien at ximian.com>
> > Blog: http://pages.infinit.net/ctech/
> >
> >
-- 
Sebastien Pouliot  <sebastien at ximian.com>
Blog: http://pages.infinit.net/ctech/