[Qgis-community-team] compiling manual & image quality

[MORREALE Jean Roc]

Otto Dassau a écrit :
> On Fri, 21 Aug 2009 13:11:40 +0200
> MORREALE Jean Roc <jr.morreale at enoreth.net> wrote:
> 
>> Otto Dassau a écrit :
>>> Hi Jean Roc,
>>>
>>> On Fri, 21 Aug 2009 11:04:10 +0200
>>> MORREALE Jean Roc <jr.morreale at enoreth.net> wrote:
>>>
>>>> Hi,
>>>>
>>>> I've been compiling the french manual for 1.0 (using texlive2008) but 
>>>> the quality of the images is very low : the jpg figuring in the final 
>>>> pdf are full of compression blocks making some captures hard to read.
>>>>
>>>> All the source's images have been localized and saved as png (96dpi) so 
>>>> I would really like to have them show up in a better quality.
>>>>
>>>> What are the right options to change ?
>>> All images are simply converted during compilation without any change of
>>> size or
>>> resolution. In the english version, many figures are screenshots with only
>>> 72dpi
>>> resolution. You are right they sometimes could be better, but I don't know
>>> of
>>> any parameter for dvipdf or dvips conversion that make the images look
>>> better,
>>> except using images with a higher resolution - just my 2c.
>>>
>>> Regards,
>>>  Otto
>>>
>> Hi Otto,
>>
>> It is not a matter of size or resolution but of jpeg artifacts due to a 
>> drastic compression, when I compare the png/eps they do not show these 
>> blocks but the jpgs included in the pdf are full of it. I think  the 
>> quality setting used by convert is below 60%, if we could get it up to 
>> 75% the images would be less blocky and still around 5% of the size of 
>> the pngs
> 
> Hi Jean Roc,
> 
> ok, but since the pdf figures are created from eps format, I wonder where
> we can improve the process since b) uses eps files created in a): 
> 
> a) convert PNG and JPEG to EPS defined in the Makefiles 
> b) create a PDF with dvipdf (a combination of dvips and ps2pdf) using EPS
> figures from a)
> 
> and when I look at the branches/1.0.0/french/user_guide folder, I don't
> see any jpeg images except the qgis logo on the front page, or am I wrong?
> 
> Can you give an example image where you think there is a big quality problem?
> 
> Regards,
>  Otto

For example take a look at startup1.0.0.png and the image as it appears 
in the pdf (here saved as a jpg but could have been exported as a tiff 
with the same defects), you can see color distorsion and noise which are 
typical of an heavy quantization step:

http://uppix.net/5/e/6/4197c43cfb28e319c4889368f40cd.png
http://uppix.net/d/a/b/83b44bd238113703618b279045a45.jpg