[gdal-dev] Unwanted partial transparency when clipping
Michael Corey
mcorey at cironline.org
Sat Jul 9 14:20:13 EDT 2011
I see -- you're right about QGIS.
I'm mostly using imagery for static or motion graphics, so my workflow
ends up in graphics software like Photoshop, After Effects and other
video, which all tend to handle imagery in roughly the same way. So I
think I'll just have to do the translation to no alpha band before
importing into those programs. I'm surprised they handle things that
differently, but it's not an impossible thing to get around.
Thanks all for your help!
Michael Corey
On 7/8/11 6:59 PM, Marius Jigmond wrote:
> I use QGIS which knows how to interpret the bands. I have no idea how
> Photoshop handles the alpha band. You can try specifying -dstnodata:
> gdalwarp -crop_to_cutline -cutline mask.shp -dstnodata "0 0 0"
> source.tif dest.tif
> this should output a RGBA tif with NoData=0 (black) and maybe
> Photoshop can interpret the NoData tag.
>
> You might also want to try nearblack:
> http://www.gdal.org/nearblack.html
>
> I suppose it would be important to know what the final purpose of
> these images is because as far as GIS software goes just about all can
> read the cropped tif just fine with proper transparency.
>
> -marius
>
> On Fri, 2011-07-08 at 18:24 -0700, Michael Corey wrote:
>> Actually when I opened up your sample file in Photoshop I got the
>> same results as I had earlier. What viewer are you using to look at
>> your output files?
>>
>> Also, I did find a workaround that at least improves the situation
>> for me.
>>
>> First I translate the source images:
>>
>> gdal_translate source1.tif source1-noalpha.tif -b 1 -b 2 -b 3 -mask 4
>> -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR --config
>> GDAL_TIFF_INTERNAL_MASK YES
>>
>> Then use warp to do my merging and clipping:
>>
>> gdalwarp -crop_to_cutline -cutline
>> ~/Documents/GIS/usa/California/doq/diablo-fullzoom-cutout.shp
>> source1-noalpha.tif source2-noalpha.tif fullzoom-clipped.tif
>>
>> I still have to use Photoshop to get rid of the nodata section, but
>> at least my transparency isn't affected.
>>
>> Any ideas how to get rid of the black and have transparent pixels
>> instead, anyone?
>>
>> Thanks again,
>> Michael Corey
>>
>> On 7/8/11 6:12 PM, Marius Jigmond wrote:
>>> 1.8 compiled from source
>>>
>>> -marius
>>>
>>> On Fri, 2011-07-08 at 18:02 -0700, Michael Corey wrote:
>>>> That certainly could be. I'm running GDAL 1.8 from the kyngchaos
>>>> site. Which version are you running?
>>>>
>>>> Thanks,
>>>> Michael Corey
>>>>
>>>> On 7/8/11 5:56 PM, Marius Jigmond wrote:
>>>>>
>>>>>
>>>>> On Fri, 2011-07-08 at 08:14 -0700, Michael Corey wrote:
>>>>>> OK, I did a little more work on this, and I've narrowed down what's
>>>>>> going on, but I could still use some help in figuring out how to solve it.
>>>>>>
>>>>>> Here's my original image:
>>>>>>
>>>>>> http://mikejcorey.com/spatial/diablo-orig-5pct.tif
>>>>>>
>>>>>> The original appears to have an RGBA setup (RGB channels and an alpha
>>>>>> channel).
>>>>>> When I run this:
>>>>>>
>>>>>> gdalwarp -crop_to_cutline -cutline cutout.shp sourceimage.tif
>>>>>> diablo-cutline.tif
>>>>>>
>>>>>> Here's what I get:
>>>>>>
>>>>>> http://mikejcorey.com/spatial/diablo-cutline-5pct.tif
>>>>>>
>>>>>> This comes out as an RGB image with no alpha channel, with each channel
>>>>>> being semi-transparent.
>>>>>>
>>>>> Not in my case. Could there be something wrong with your GDAL
>>>>> setup? I drew a shapefile mask and ran the above command but my
>>>>> result is RGBA, the alpha band is not lost. See mask and result here:
>>>>> http://ubuntuone.com/p/13WR/
>>>>>
>>>>> the output of gdalinfo:
>>>>> marius at mobi <mailto:marius at mobi>:~/Downloads$ gdalinfo
>>>>> diablo_cutl.tif
>>>>> Driver: GTiff/GeoTIFF
>>>>> Files: diablo_cutl.tif
>>>>> Size is 266, 224
>>>>> Coordinate System is:
>>>>> PROJCS["NAD83 / UTM zone 10N",
>>>>> GEOGCS["NAD83",
>>>>> DATUM["North_American_Datum_1983",
>>>>> SPHEROID["GRS 1980",6378137,298.2572221010002,
>>>>> AUTHORITY["EPSG","7019"]],
>>>>> AUTHORITY["EPSG","6269"]],
>>>>> PRIMEM["Greenwich",0],
>>>>> UNIT["degree",0.0174532925199433],
>>>>> AUTHORITY["EPSG","4269"]],
>>>>> PROJECTION["Transverse_Mercator"],
>>>>> PARAMETER["latitude_of_origin",0],
>>>>> PARAMETER["central_meridian",-123],
>>>>> PARAMETER["scale_factor",0.9996],
>>>>> PARAMETER["false_easting",500000],
>>>>> PARAMETER["false_northing",0],
>>>>> UNIT["metre",1,
>>>>> AUTHORITY["EPSG","9001"]],
>>>>> AUTHORITY["EPSG","26910"]]
>>>>> Origin = (693798.721929854014888,3902305.751849883235991)
>>>>> Pixel Size = (20.022668877344305,-20.040546259961307)
>>>>> Metadata:
>>>>> AREA_OR_POINT=Area
>>>>> Image Structure Metadata:
>>>>> INTERLEAVE=PIXEL
>>>>> Corner Coordinates:
>>>>> Upper Left ( 693798.722, 3902305.752) (120d52'12.04"W,
>>>>> 35d14'42.43"N)
>>>>> Lower Left ( 693798.722, 3897816.669) (120d52'15.84"W,
>>>>> 35d12'16.81"N)
>>>>> Upper Right ( 699124.752, 3902305.752) (120d48'41.44"W,
>>>>> 35d14'38.67"N)
>>>>> Lower Right ( 699124.752, 3897816.669) (120d48'45.35"W,
>>>>> 35d12'13.05"N)
>>>>> Center ( 696461.737, 3900061.211) (120d50'28.67"W,
>>>>> 35d13'27.75"N)
>>>>> Band 1 Block=266x7 Type=Byte, ColorInterp=Red
>>>>> Mask Flags: PER_DATASET ALPHA
>>>>> Band 2 Block=266x7 Type=Byte, ColorInterp=Green
>>>>> Mask Flags: PER_DATASET ALPHA
>>>>> Band 3 Block=266x7 Type=Byte, ColorInterp=Blue
>>>>> Mask Flags: PER_DATASET ALPHA
>>>>> Band 4 Block=266x7 Type=Byte, ColorInterp=Alpha
>>>>>
>>>>> -marius
>>>>>
>>>>>> However, if I do this:
>>>>>>
>>>>>> gdalwarp -dstalpha -crop_to_cutline -cutline cutout.shp sourceimage.tif
>>>>>> diablo-dstalpha-cutline.tif
>>>>>>
>>>>>> I get this:
>>>>>>
>>>>>> http://mikejcorey.com/spatial/diablo-dstalpha-cutline-5pct.tif
>>>>>>
>>>>>> This one is strange, because it appears to be a grayscale image. But
>>>>>> when I open it in Photoshop, I see that it actually has 4 alpha
>>>>>> channels. I suspect that those are just getting set incorrectly as alpha
>>>>>> and are in fact the RGB channels, but can someone explain that behavior
>>>>>> or how to fix it?
>>>>>>
>>>>>> What I want to end up with is a clipped RGB image (or RGBA) image where
>>>>>> nodata is transparent and the RGB isn't translucent.
>>>>>>
>>>>>> Thanks again!
>>>>>>
>>>>>> Michael Corey
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 7/7/11 7:13 AM, Eli Adam wrote:
>>>>>> > Michael,
>>>>>> >
>>>>>> >>>> On 7/6/2011 at 5:35 PM, in message<4E14FF42.50903 at cironline.org <mailto:4E14FF42.50903 at cironline.org>>, Michael
>>>>>> > Corey<mcorey at cironline.org <mailto:mcorey at cironline.org>> wrote:
>>>>>> >> Sure, I've uploaded samples here.
>>>>>> >>
>>>>>> >> http://www.mikejcorey.com/spatial/diablo-box-sample.tif
>>>>>> >> http://www.mikejcorey.com/spatial/diablo-cutout-sample.tif
>>>>>> > I don't notice the semi-transparency in these scaled down images. Perhaps it is the way your viewer reads the mask?
>>>>>> >
>>>>>> >> These are the same as the images created by the process I described (but
>>>>>> >> scaled down).
>>>>>> >>
>>>>>> >> To your point about specifying size in the first step -- will that make
>>>>>> >> the process run faster, or does it do the scaling down after it builds
>>>>>> >> the full-resolution image?
>>>>>> >>
>>>>>> >> Also, I notice that my filesize always gets significantly bigger when I
>>>>>> >> do the cutout step, which seems counter-intuitive to me since in theory
>>>>>> >> shouldn't there be less information present once the cutout is done?
>>>>>> > -cutline does not 'discard' any data. The extent of the data remains the same unless you reset those extents. You can do that with -crop_to_cutline. Here are some details from the gdalwarp page,http://gdal.org/gdalwarp.html :
>>>>>> >
>>>>>> > -crop_to_cutline:
>>>>>> > (GDAL>= 1.8.0) Crop the extent of the target dataset to the extent of the cutline.
>>>>>> >
>>>>>> > Polygon cutlines may be used as a mask to restrict the area of the destination file that may be updated, including blending. If the OGR layer containing the cutline features has no explicit SRS, the cutline features must be in the georeferenced units of the destination file. When outputing to a not yet existing target dataset, its extent will be the one of the original raster unless -te or -crop_to_cutline are specified.
>>>>>> >
>>>>>> > Best Regards, Eli
>>>>>> >
>>>>>> >> Thanks for your help!
>>>>>> >>
>>>>>> >> Michael Corey
>>>>>> >>
>>>>>> >>
>>>>>> >> On 7/6/11 5:01 PM, Chaitanya kumar CH wrote:
>>>>>> >>> Michael,
>>>>>> >>>
>>>>>> >>> Can you provide screenshots of
>>>>>> >>> diablo-combined-center-utm10-70pct-box.tif and
>>>>>> >>> diablo-combined-center-utm10-70pct-cutout.tif for comparison?
>>>>>> >>>
>>>>>> >>> By the way, you can perform the actions of the two gdal_translate
>>>>>> >>> commands in the first step with the gdal_merge.py script itself unless
>>>>>> >>> you want to use a specific resampling algorithm.
>>>>>> >>>
>>>>>> >>> On Thu, Jul 7, 2011 at 4:28 AM, Michael Corey<mcorey at cironline.org <mailto:mcorey at cironline.org>
>>>>>> >>> <mailto:mcorey at cironline.org>> wrote:
>>>>>> >>>
>>>>>> >>> Hi all:
>>>>>> >>>
>>>>>> >>> I'm using a shapefile as a clipping mask to cut out the shoreline
>>>>>> >>> from some DOQ files that I have merged together. But when I do the
>>>>>> >>> clipping step, I end up with unwanted semitransparency in the
>>>>>> >>> non-clipped areas.
>>>>>> >>>
>>>>>> >>> I'm pretty sure the problem is only with my gdalwarp step at the end.
>>>>>> >>>
>>>>>> >>> Here's my process:
>>>>>> >>>
>>>>>> >>> gdal_merge.py -init "255" -o diablo-combined-center-utm10.tif file
>>>>>> >>> file file file
>>>>>> >>>
>>>>>> >>> gdal_translate -outsize 70% 70% diablo-combined-center-utm10.tif
>>>>>> >>> diablo-combined-center-utm10-70pct.tif
>>>>>> >>>
>>>>>> >>> ogrinfo -al ./diablo_canyon_detail_clipper.shp
>>>>>> >>> //Extent: (XXXX, YYYY) - (XXXX, YYYY)
>>>>>> >>>
>>>>>> >>> gdal_translate -projwin XXXX YYYY XXXX YYYY
>>>>>> >>> diablo-combined-center-utm10-70pct.tif
>>>>>> >>> diablo-combined-center-utm10-70pct-box.tif
>>>>>> >>>
>>>>>> >>> gdalwarp -co COMPRESS=DEFLATE -cutline
>>>>>> >>> ./diablo_canyon_detail_clipper.shp
>>>>>> >>> diablo-combined-center-utm10-70pct-box.tif
>>>>>> >>> diablo-combined-center-utm10-70pct-cutout.tif
>>>>>> >>>
>>>>>> >>> Can anyone help?
>>>>>> >>>
>>>>>> >>> Thanks!
>>>>>> >>>
>>>>>> >>> --
>>>>>> >>> Michael Corey
>>>>>> >>>
>>>>>> >>> _______________________________________________
>>>>>> >>> gdal-dev mailing list
>>>>>> >>> gdal-dev at lists.osgeo.org <mailto:gdal-dev at lists.osgeo.org><mailto:gdal-dev at lists.osgeo.org>
>>>>>> >>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>>>> >>>
>>>>>> >>>
>>>>>> >>>
>>>>>> >>>
>>>>>> >>> --
>>>>>> >>> Best regards,
>>>>>> >>> Chaitanya kumar CH.
>>>>>> >>> /t?a???nj?/ /k?m?r/
>>>>>> >>> +91-9494447584
>>>>>> >>> 17.2416N 80.1426E
>>>>>> _______________________________________________
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