[mapserver-users] Output image resolution - explanation needed

[Dejan.Gambin at pula.hr]

Thanks, you helped me a lot

In my example, I have printed an area of aproximately 1km wide on an A4 
Landscape that is 29,7cm wide, so 1inch is about 85.5m. So that should be 
the reason? :-)

regards, dejan

"Rahkonen Jukka" <Jukka.Rahkonen at mmmtike.fi> wrote on 31.07.2008 11:00:15:

> Hi,
> 
> What are the dimensions of the image you have captured in real world
> utits?  Your original aerial images have half a metre pixel size. 
> It mean that at 300 dpi one original image pixel corresponds with 
> one pixel at paper if square inch on your printout is presenting 
> exactly 150 by 150 meters in nature.  That is the maximum quality 
> you can achieve.  If square inch on paper equals to 75 by 75 meters 
> the maximum quolity is achieved already at 150 dpi. Multiplicating 
> original image pixels for printing cannot improve the quality.  But 
> if you have zoomed out so far that creating output image means 
> downsampling the original imagery you should see the differense. 
> So, if your 2150x1111 low resolution image is covering a 
> considerably larger area than 1075x555 meters in real world it 
> should look better when downloaded at 300 dpi with 4300x2222 pixels. 
> 
> -Jukka Rahkonen-
> 
> 
> 
> Lähettäjä: mapserver-users-bounces at lists.osgeo.org [mailto:
> mapserver-users-bounces at lists.osgeo.org] Puolesta Dejan.Gambin at pula.hr
> Lähetetty: 31. heinäkuuta 2008 9:32
> Vastaanottaja: mapserver-users at lists.osgeo.org
> Aihe: Re: [mapserver-users] Output image resolution - explanation needed

> 
> Thanks Steve 
> 
> I still (unfortunatelly) don't understand why I am getting the "same
> quality" image on the paper with the first and second print (the 
> second image has twice more pixels). Is it because of the input 
> image itself? To be specific - the raster input is aerial image that
> gdalinfor reports as: 
> 
> Driver: GTiff/GeoTIFF 
> Files: 5C14-05-DOF.tif 
> Size is 4500, 6000 
> Coordinate System is `' 
> Origin = (5419000.154658853100000,4964998.794652804700000) 
> Pixel Size = (0.499829146050620,-0.499829146050620) 
> Corner Coordinates: 
> Upper Left  ( 5419000.155, 4964998.795) 
> Lower Left  ( 5419000.155, 4961999.820) 
> Upper Right ( 5421249.386, 4964998.795) 
> Lower Right ( 5421249.386, 4961999.820) 
> Center      ( 5420124.770, 4963499.307) 
> Band 1 Block=256x256 Type=Byte, ColorInterp=Red 
>   Overviews: 2250x3000, 1125x1500, 563x750, 282x375 
> Band 2 Block=256x256 Type=Byte, ColorInterp=Green 
>   Overviews: 2250x3000, 1125x1500, 563x750, 282x375 
> Band 3 Block=256x256 Type=Byte, ColorInterp=Blue 
>   Overviews: 2250x3000, 1125x1500, 563x750, 282x375 
> 
> regards, dejan 
> 
> "Steve Lime" <Steve.Lime at dnr.state.mn.us> wrote on 30.07.2008 21:13:55:
> 
> > Resolution in MapServer-speak is referring to the resolution of the 
> > output device a map
> > will be displayed on. The value is used for scale computations and 
> > nothing else. It does not
> > affect the size (in pixels) of MapServer. Scale values do impact the
> > size at which features
> > and text are rendered IF scaling (via SYMBOLSCALE) is turned on. 
> > Higher quality output is
> > usually a matter of having more pixels to print, however you usually
> > want larger features
> > too which is where the resolution parameter combined with scaling can 
help.
> > 
> > Steve
> > 
> > >>> On 7/30/2008 at 2:21 AM, in message
> > <OF8A10F31F.0E3F1C94-ONC1257496.0026AB23-C1257496.00286464 at pula.hr>,
> > <Dejan.Gambin at pula.hr> wrote:
> > > Hi,
> > > 
> > > I am trying to download a high resolution image and print it on 
> a paper. I 
> > > am using p.mapper and its download function that enables downloading 
the 
> > > map image on different resolutions. 
> > > 
> > > I have turned on my raster layer (ortophoto image). I have 
> zoomed in to an 
> > > area of interest. I have downloaded the map twice - with a 
resolution of 
> > > 150 and 300. The image is shown i a new page/tab (firefox). I right 
click 
> > > on the image and save it as a png (also tried with a jpeg) file.Now, 
the 
> > > first file is 2150x1111 pixels, 120 dpi vertical and horizontal 
> resolution 
> > > (right click on a file, properties, summary, what does it mean?), 
the 
> > > second file is 4300x2222 pixels, 120 dpi vertical and horizontal 
> > > resolution. Seems ok. The second image is "doubled" in pixel size.
> > > 
> > > Now, when I try to print this image on A4 paper, using 300dpi, the 
images 
> > > are the same, there is no "better quality" in second image.
> > > 
> > > I have just finshed reading the Mapserver thread on "Change image 
> > > resolution in mapfile". Several limitations are mentioned there - 
max. 
> > > image size supported by Mapserver, "resolution" value/tag embedded 
in 
> > > output format, etc. Can it be related to my problem? Or is it maybe 
that 
> > > software I am using to print this image doesn't "use" this extra 
pixels? 
> > > Or I am just missing some basic stuff I need to know :-(
> > > 
> > > 
> > > thanks very much on any explanation
> > > 
> > > regards, dejan
> > 
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