[FWTools] gdal translate - air photo seems washed out after converting image

[Brent Fraser]

Mark,

   You could try doing a "gdalinfo -stats" to get the min/max pixel 
values, then do a "gdal_translate -scale" to stretch the min/max values 
to 0 255 (the full range of an 8-bit band).

   You may be able to do the same thing in mapserver by referencing a 
GDAL vrt file with a LUT entry to do the exact same thing as the above 
gdal_translate command, but it would be [almost] pointless (and there 
would be a performance hit).

Best Regards,
Brent Fraser

On 7/11/2013 8:07 AM, Mark Volz wrote:
>
> Richard,
>
> I partially figured it out, but I still could use some help.
>
> The problem that I had was not with the created image itself, but how 
> ESRI displayed it.  By default ArcMap uses no stretch to display the 
> SID image while it uses a percent clip stretch for the created tif .  
> After I changed the stretch from percent clip to none the images 
> appeared almost the same, but there was still some differences.  Next, 
> I changed the stretch to minimum-maximum on the created tif image and  
> I could not tell any difference between the sid file and the tif image.
>
> Questions:
>
> 1)When creating a tiff file in gdal_translate, can I adjust settings 
> so that the new image will appear exactly like the old image without 
> having to turn stretch to minimum-maximum?
>
> 2)Is there a way in mapserver to change the stretch from none to 
> minimum maximum (or other types of stretches if desired) and if so is 
> there a performance hit?
>
> 3)Is there a way to modify a tiff file so that any GIS program 
> including ArcGIS that opens up the file will use the correct stretch 
> type, or is there a setting within ArcGIS that will always use a 
> certain type of stretch when it opens up tiff images?
>
> Thanks
>
> Mark Volz, GISP
>
> GIS Specialist
>
> *From:*Richard Greenwood [mailto:richard.greenwood at gmail.com]
> *Sent:* Wednesday, July 10, 2013 6:32 PM
> *To:* Mark Volz
> *Cc:* fwtools at lists.maptools.org
> *Subject:* Re: [FWTools] gdal translate - air photo seems washed out 
> after converting image
>
> On Wed, Jul 10, 2013 at 3:08 PM, Mark Volz <MarkVolz at co.lyon.mn.us 
> <mailto:MarkVolz at co.lyon.mn.us>> wrote:
>
> Hello,
>
> I converted a mr sid air photo to a tif file.  The colors appear 
> washed out and too bright compared to the mr sid file.
>
>
> I would like to create an image file that has the following three 
> characteristics:
>
> 1) Fast for Mapserver to read.
> 2) Relatively the same size as the MrSID file.  - I would prefer a 
> file size that is no larger than twice the size of the Mr SID file, 
> even if it means that I have to take a small hit by using compression
> 3) retains the same image quality as the original MrSID file
>
> The following two commands made the image fast for mapserver, and 
> relatively small.  But the colors were washed out...
>
> c:\ms4w\apps\PipestoneMaps\Raster\Picto2013>gdal_translate -CO 
> TILED=YES -CO PHOTOMETRIC=YCBCR -CO TFW=YES -CO COMPRESS=JPEG -CO 
> BIGTIFF=YES MNPIPE13-SID-9INCH.sid New.tif
> c:\ms4w\apps\PipestoneMaps\Raster\Picto2013>gdaladdo -r average 
> --config compress_overview JPEG --config photometric_overview YCBCR 
> New.tif 2 4 8 16 32 64 128 256
>
>
> What can I do to improve the image quality, while retaining the speed 
> and a moderate file size?
>
> Thanks
>
> Mark Volz, GISP
> GIS Specialist
>
> Mark,
>
> Those are pretty much the commands that I regularly use to prepare 
> imagery for mapserver. I have never experienced any noticeable color 
> distortion. What does it look like with a straight
>    gdal_translate MNPIPE13-SID-9INCH.sid New.tif
>
> obviously that's not what you want for a final product, but it would 
> be my first step toward 'debugging' the problem.
>
> Rich
>
>
> -- 
> Richard Greenwood
> richard.greenwood at gmail.com <mailto:richard.greenwood at gmail.com>
> www.greenwoodmap.com <http://www.greenwoodmap.com>
>
>
>
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