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nf-wiamdef-wiasdownsamplebuffer.md

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UID title description tech.root ms.date keywords ms.keywords req.header req.include-header req.target-type req.target-min-winverclnt req.target-min-winversvr req.kmdf-ver req.umdf-ver req.ddi-compliance req.unicode-ansi req.idl req.max-support req.namespace req.assembly req.type-library req.lib req.dll req.irql targetos req.typenames f1_keywords topic_type api_type api_location api_name
NF:wiamdef.wiasDownSampleBuffer
wiasDownSampleBuffer function (wiamdef.h)
The wiasDownSampleBuffer function takes in a buffer of DWORD-aligned pixel data and downsamples it (produces image data of lower resolution) to the specified size and resolution.
image
01/04/2023
wiasDownSampleBuffer function
image.wiasdownsamplebuffer, wiamdef/wiasDownSampleBuffer, wiasDownSampleBuffer, wiasDownSampleBuffer function [Imaging Devices], wiasFncs_a109a3d9-e801-4332-bc89-65432023eecb.xml
wiamdef.h
Wiamdef.h
Desktop
Wiaservc.lib
Wiaservc.dll
Windows
wiasDownSampleBuffer
wiamdef/wiasDownSampleBuffer
APIRef
kbSyntax
DllExport
Wiaservc.dll
wiasDownSampleBuffer

-description

The wiasDownSampleBuffer function takes in a buffer of DWORD-aligned pixel data and downsamples it (produces image data of lower resolution) to the specified size and resolution.

-parameters

-param lFlags

Specifies a set of flags that determine the behavior of this function. Currently, only the following flag is defined.

Flag Meaning
WIAS_GET_DOWNSAMPLED_SIZE_ONLY Do not copy the downsampled data to the destination buffer. Instead, set the following members of the WIAS_DOWN_SAMPLE_INFO structure: ulDownSampledHeight, ulDownSampleWidth, ulAlignedHeight, ulAlignedWidth.

-param pInfo [in, out]

Pointer to the WIAS_DOWN_SAMPLE_INFO structure that contains all of the information needed for the downsampling operation.

-returns

On success, the function returns S_OK.

If the function fails, it returns a standard COM error or one of the WIA error codes.

-remarks

The wiasDownSampleBuffer function can be used in either of the following two ways:

  • The caller specifies the downsampled (that is, output) width and height by setting the ulDownSampledWidth and ulDownSampledHeight members of the WIA_DOWN_SAMPLE_INFO structure.

  • The caller sets the ulDownSampledWidth and ulDownSampledHeight members of the WIA_DOWN_SAMPLE_INFO structure to zero, indicating that the function should choose the output width and height.

To see what output width and height values the function chooses, call this function with the lFlags parameter set to WIAS_GET_DOWNSAMPLED_SIZE_ONLY. On return, the ulDownSampledWidth and ulDownSampledHeight members are set to their new values. No downsampling is performed in this case.

The caller of this function is required to fill in the following members of the WIA_DOWN_SAMPLE_INFO structure:

  • ulOriginalWidth

  • ulOriginal Height

  • ulBitsPerPixel

  • ulXRes

  • ulYRes

  • pSrcBuffer

The wiasDownSampleBuffer function expects ulBitsPerPixel to be 1, 8, or 24, corresponding to 1-, 8-, and 24-bit-per-pixel data. The caller can also specify the size of the downsampled data by filling in the following WIA_DOWN_SAMPLE_INFO structure members: - ulDownSampledWidth ulDownSampledHeight

If the buffer that receives the downsampled data has already been allocated, the caller should fill in these WIA_DOWN_SAMPLE_INFO structure members:

  • ulDestBufSize

  • ulSrcBufSize

  • pDestBuffer

If the caller sets pDestBuffer to NULL, the destination buffer is allocated by the WIA service. On return from this function, pDestBuffer points to the destination buffer. The caller is responsible for freeing this memory when the operation is finished, and does this by calling CoTaskMemFree on the buffer.

Because this function is not able to produce partial output lines, the number of scan lines in the input buffer must be an integer multiple of the scaling factor. For example, suppose the input buffer contains an image sampled at 600 dpi, which you intend to downsample to an equivalent 50 dpi image. In this case, you are scaling down the original image by a factor of 12 (because 600 / 50 = 12). This means that the function must receive 12 input lines for each output line that it produces.

If the original image has a resolution of Rin dpi, and is to be scaled down to an image with a resolution of Rout dpi, the scale-down factor is Rin / Rout, and the number of lines in the input buffer should be a multiple of Rin / Rout. If the scan head reaches the last band of the original image, and there are too few scan lines in the input buffer to produce an output line, pad the input buffer so that it contains the required number of data lines. Failure to do so causes unpredictable results, and can even result in a driver crash.

-see-also

WIAS_DOWN_SAMPLE_INFO