openslide_read_region returns no picture data

[Stefan König]

here is a part of my sample script to play bit arround with openslide,
before i use this productive:

	openslide_read_region(slideObject, dst, 0, 0, 1, *width, *height);
	
	if(openslide_get_error(slideObject))
		std::cout << openslide_get_error(slideObject) << std::endl;

	argb8c_view_t gil = boost::gil::interleaved_view(*width, *height,
(const argb8c_pixel_t*) (dst), (*width)*4);

	rgb8_image_t exp(*width,*height);
	copy_and_convert_pixels(gil, view(exp));

	jpeg_write_view("C:\\readRegionTest.jpg", view(exp));

	std::cout << "***************************************" << std::endl;
	std::cout << "finished region read" << std::endl;
	std::cout << "***************************************" << std::endl;


	int64_t* w = new int64_t;
	int64_t* h = new int64_t;
	const char* name = openslide_get_associated_image_names(slideObject)[1];
	openslide_get_associated_image_dimensions (slideObject, name, w, h);
	uint32_t* dst2 = new uint32_t[(*w)*(*h)*4];
	openslide_read_associated_image (slideObject, name, dst2);

	if(openslide_get_error(slideObject))
		std::cout << openslide_get_error(slideObject) << std::endl;

	argb8c_view_t gil2 = boost::gil::interleaved_view(*w, *h, (const
argb8c_pixel_t*) (dst2), *w*4);

	rgb8_image_t exp2(*w,*h);
	copy_and_convert_pixels(gil2, view(exp2));

	jpeg_write_view("C:\\readAssociatedRegionTest.jpg", view(exp2));

	std::cout << "***************************************" << std::endl;
	std::cout << "finished associated region read" << std::endl;
	std::cout << "***************************************" << std::endl;

this is my output:

the second picture is created successfully, the first one is only
black (the dst pointer is empty.), i executed this script by using the
mirax sample files from the openslide project page.

***************************************
***************************************
finished region read
***************************************
***************************************
finished associated region read
***************************************


2010/12/8 Stefan König <blogdde at googlemail.com>:
> The error state is empty and a read_associated_image call works fine aber
> calling read_region.
>
> I debugged inside the read_region code, I think there is something wrong
> with some of the cairo calls painting to the buffer, but there is no proof
> yet.
>
> Friday I'll take a further look, and I'll write here if I find something.
>
>
> -----Ursprüngliche Nachricht-----
> Von: openslide-users-bounces+blogdde=googlemail.com at lists.andrew.cmu.edu
> [mailto:openslide-users-bounces+blogdde=googlemail.com at lists.andrew.cmu.edu]
> Im Auftrag von Jan Harkes
> Gesendet: Mittwoch, 8. Dezember 2010 17:13
> An: openslide-users at lists.andrew.cmu.edu
> Betreff: Re: openslide_read_region returns no picture data
>
> On 12/08/2010 10:21 AM, Stefan König wrote:
>> Hi,
>>
>> i try to read a single region out of mirax file (just tried my own and
>> the sample files from openslide.org), if i use
>> openslide_get_associated_image_dimensions() i can extract my image and
>> save work with them but if i try to extract a image by using
>> openslide_read_region my dst pointer contains nothing and there is no
>> exception either :(
>>
>>       *width = 256;
>>       *height = 256;
>>
>>       uint32_t* dst = new uint32_t[(*width)*(*height)*4];
>>       openslide_read_region(slideObject, dst, 0, 0, 1, *width, *height);
>>
>> if i understand the documentation right, it should take my slide
>> object and write a 256x256 area begining at topleft from layer to dst?
>
> I believe that that should work. But it may be that the slideObject
> handle got into an error state, you probably should check for errors by
> calling 'openslide_get_error' after the call to openslide_read_region
> and probably most other calls.
>
> According to the C api documentation, when the object is in error state
> openslide_read_region will clear the dst buffer instead of painting to it.
>
> Jan
>
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