[gdal-dev] Problem using image bands

[jcurru]

Ouch!

Thank you very much, Even. I should have asked sooner, instead of going to bed at 5 in the morning... :-)
Yes, I have to read into a RGB buffer, but your solution would increase a lot the loading time for other images that are working well.

I have read this: http://trac.osgeo.org/gdal/changeset/25107. So, do you recommend me to change the code in ecwdataset.cpp and rebuild the library?

Thanks again!
 
José Antonio Carmena Flores


>________________________________
> De: Even Rouault [via OSGeo.org] <ml-node+s1560n5009874h37 at n6.nabble.com>
>Para: jcurru <jcurru at yahoo.es> 
>Enviado: Viernes 19 de octubre de 2012 14:42
>Asunto: Re: Problem using image bands
> 
>
>Selon jcurru <[hidden email]>: 
>
>
>> Hello! 
>> 
>> I have a problem reading an ECW image. I want to read the image using only 
>> the first band. So I use: 
>> int bmap[3] = {1,1,1}; 
>> 		GDALImage->RasterIO( 
>> 			GF_Read, 
>> 			x,       		// int nXOff, 
>> 			y,       		// int nYOff, 
>> 			dx, 	     	// int nXSize, 
>> 			dy, 	     	// int nXSize, 
>> 			buffer,		 	// void* pData, 
>> 			xBufSize,       // int nBufXSize, 
>> 			yBufSize,       // int nBufYSize, 
>> 			GDT_Byte,	 	// GDALDataType eBufType, 
>> 			3,			 	// int nBandCount, 
>> 			bmap,		 	// int* panBandMap, 
>> 			3,			 	// int nPixelSpace, 
>> 			xBufSize * 3,   // int nLineSpace, 
>> 			1			 	// int nBandSpace 
>> 			); 
>> This is working well with some ECW images (they show as grayscale) but it 
>> does not with another, big ECW. It shows in full RGB color, exactly the same 
>> as if I had written int bmap[3] = {1,2,3}; 
>I suppose you are using the 3.3 version of the ECW SDK ? Then, it is a known 
>issue in the SDK itself. See http://trac.osgeo.org/gdal/ticket/4234 . A work 
>around has been committed in the GDAL 2.0dev version just a few days ago. 
>
>For currently released GDAL versions, if you only want to read one band, you 
>could just use RasterIO() on the band object, instead of the whole dataset. If 
>you need to read it into a RGB buffer, you just need to keep the pixel space and 
>line space you've used in the above call, and after calling RasterIO() on the 
>band, do a loop to copy each buffer[3*i] value into buffer[3*i+1] and 
>buffer[3*i+2] 
>
>
>> 
>> Any idea? 
>> Thanks in advance! 
>> 
>> 
>> 
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