Re: [Digilib-devel] last row filled with black pixels

[Robert C. <ca...@mp...>]

Hi Mathias,

On 28.04.14 11:36, Mathias Göbel wrote:
> Thank you very much for your reply.
> My current version is2.2.2
> (/META-INF/maven/digilib/digilib-webapp/pom.xml).

The fix for (at least somewhat) improved precision got in later than the
2.2.2 release. I would suggest to try one of the daily builds of the
2.3-SNAPSHOT line if you can:

http://it-dev.mpiwg-berlin.mpg.de/downloads/digilib/daily-build/

I could try to create an updated 2.2.3 with only that fix if there is
sufficient interest in that. Personally I would prefer to release a
2.3.0 with the current code in the near future.

I you have any problems just ask.

Cheers
	Robert

> I see this issue is not exclusive to my server configuration. But I am
> not able to fix this code at the moment - I am not a computer scientist
> and there is the well known lack of time.
> 
> I definitely prefer transparent pixels - the parameter &mo=png did the
> trick for now, but i will update asap.
> I may set up a post-processing instruction, that prove the rendered
> image size in comparison to the expected value. A CSS instruction can
> refine the image by placing it in a container with the correct size.
> One can do it with JS and/or JS libraries like pixastic
> <http://www.pixastic.com/lib/> as well. Digital editions are rather
> static and after the publication cached images can help to remove the
> libraries overhead.
> 
> Best,
> Mathias
> 
> 
> 
> On 24.04.2014 15:46, Robert Casties wrote:
>> Hi Mathias,
>>
>> On 24.04.14 12:55, Mathias Göbel wrote:
>>> I use the digilib scaler to extract parts of larger images and
>>> include them in a
>>> digital edition. I recently observed an reproducible issue. Some
>>> images returned
>>> by the scaler come with a (last) row and (last) column filled with
>>> black pixels.
>>> You can see an example here:
>>>  
>>> >>http://141.5.101.102/digilib/Scaler?&fn=C07_062.jpg&dw=500&dh=500&wx=0.49559520812353136&wy=0.16589224303043199&ww=0.3766523581738838&wh=0.3066492977229197
>>>
>>>
>>>
>>> I wonder why the resulting images width is 501px, but dw is set to 500.
>>> If I change the dh/dw parameters, the results comes - as expected -
>>> without the
>>> black lines.
>>> http://141.5.101.102/digilib/Scaler?&fn=C07_062.jpg&dw=1500&dh=1500&wx=0.49559520812353136&wy=0.16589224303043199&ww=0.3766523581738838&wh=0.3066492977229197
>>>
>>> But the result is still one pixel larger than the parameter defines.
>> digilib has some rounding issues especially with high zoom factors which
>> lead to wrong calculations of the resulting image size. Depending on the
>> image format additional pixels are either black (from JPG) or
>> transparent (PNG from TIFF).
>>
>> Which version of digilib are you using? The precision of calculations
>> was improved in October 2013 (Scaler version 2.2.3
>> <http://sourceforge.net/p/digilib/code/ci/21441a3f52085048378806b8c0eeff21e0bd3a64/>)
>>
>> but there are still issues with big zoom factors.
>>
>> The current code that calculates sizes (getScaleXY and related in
>> http://sourceforge.net/p/digilib/code/ci/tip/tree/common/src/main/java/digilib/image/ImageJobDescription.java)
>>
>> has rather complicated side-effects and I haven't found the core of the
>> rounding problem yet. (patches are welcome :-)
>>
>> Best
>>     Robert
>>