I am trying to use the Windows Directshow API to capture still images using a UVC camera. I am using this article from Microsof(https://learn.microsoft.com/en-us/windows/win32/directshow/capturing-an-image-from-a-still-image-pin) to implement this. I want to be able to capture still images at different exposures so I can later use OpenCV to create an HDR image with them. I am aware that Directshow is a legacy feature. I ended up using it as it was the only API that had an example of how to implement still image capture for uvc cameras.
I tried setting the camera exposure before the still image trigger(pAMVidControl->SetMode(pPin, VideoControlFlag_Trigger) using the IAMCameraControl interface(https://learn.microsoft.com/en-us/windows/win32/api/strmif/nn-strmif-iamcameracontrol). I can see the exposure change in the preview feed but it gets reset on hitting the SetMode trigger command to some value x(not sure what value it is). The still image captured thus has a different exposure(x) to what I set it to. Is there a different interface for setting the camera exposure for still image capture?
Here is a sample of what I am trying to do. Unfortunately its quite long due to the additional stuff I have to add on to get directshow to work.
#include <dshow.h>
#include <iostream>
EXTERN_C const CLSID CLSID_NullRenderer;
EXTERN_C const CLSID CLSID_SampleGrabber;
static
const
IID IID_ISampleGrabber = { 0x6B652FFF, 0x11FE, 0x4fce, { 0x92, 0xAD, 0x02, 0x66, 0xB5, 0xD7, 0xC7, 0x8F } };
class __declspec(uuid("{C1F400A0-3F08-11D3-9F0B-006008039E37}")) SampleGrabber;
#pragma region SampleGrabber
struct __declspec(uuid("0579154a-2b53-4994-b0d0-e773148eff85"))
ISampleGrabberCB : IUnknown
{
//
// Raw methods provided by interface
//
virtual HRESULT __stdcall SampleCB (
double SampleTime,
struct IMediaSample * pSample ) = 0;
virtual HRESULT __stdcall BufferCB (
double SampleTime,
unsigned char * pBuffer,
long BufferLen ) = 0;
};
struct __declspec(uuid("6b652fff-11fe-4fce-92ad-0266b5d7c78f"))
ISampleGrabber : IUnknown
{
//
// Raw methods provided by interface
//
virtual HRESULT __stdcall SetOneShot (
long OneShot ) = 0;
virtual HRESULT __stdcall SetMediaType (
struct _AMMediaType * pType ) = 0;
virtual HRESULT __stdcall GetConnectedMediaType (
struct _AMMediaType * pType ) = 0;
virtual HRESULT __stdcall SetBufferSamples (
long BufferThem ) = 0;
virtual HRESULT __stdcall GetCurrentBuffer (
/*[in,out]*/ long * pBufferSize,
/*[out]*/ long * pBuffer ) = 0;
virtual HRESULT __stdcall GetCurrentSample (
/*[out,retval]*/ struct IMediaSample * * ppSample ) = 0;
virtual HRESULT __stdcall SetCallback (
struct ISampleGrabberCB * pCallback,
long WhichMethodToCallback ) = 0;
};
struct __declspec(uuid("c1f400a0-3f08-11d3-9f0b-006008039e37"))
SampleGrabber;
// [ default ] interface ISampleGrabber
#pragma endregion
// DirectShow objects
HRESULT hr;
ICreateDevEnum *pDevEnum = NULL;
IEnumMoniker *pEnum = NULL;
IMoniker *pMoniker = NULL;
IPropertyBag *pPropBag = NULL;
IGraphBuilder *pGraph = NULL;
ICaptureGraphBuilder2 *pBuilder = NULL;
IBaseFilter *pCap = NULL;
IBaseFilter *pSampleGrabberFilter = NULL;
IBaseFilter *pSampleGrabberStillFilter = NULL;
ISampleGrabber *pSampleGrabber = NULL;
ISampleGrabber *pSampleGrabberStill = NULL;
IBaseFilter *pNullRenderer = NULL;
IBaseFilter *pNullRendererStill = NULL;
IMediaControl *pMediaControl = NULL;
IAMVideoControl *pAMVidControl = NULL;
IAMCameraControl *pAMVCamControl = NULL;
int img_index = 0;
AM_MEDIA_TYPE g_StillMediaType;
// Find the still pin.
IPin *pPin = NULL;
char *pBuffer = NULL;
void exit_message(const char* error_message, int error)
{
// Print an error message
fprintf(stderr, error_message);
fprintf(stderr, "\n");
// Clean up DirectShow / COM stuff
if (pBuffer != NULL) delete[] pBuffer;
if (pMediaControl != NULL) pMediaControl->Release();
if (pNullRenderer != NULL) pNullRenderer->Release();
if (pNullRendererStill != NULL) pNullRendererStill->Release();
if (pSampleGrabber != NULL) pSampleGrabber->Release();
if (pSampleGrabberStill != NULL) pSampleGrabberStill->Release();
if (pSampleGrabberFilter != NULL) pSampleGrabberFilter->Release();
if (pSampleGrabberStillFilter != NULL) pSampleGrabberStillFilter->Release();
if (pCap != NULL) pCap->Release();
if (pBuilder != NULL) pBuilder->Release();
if (pGraph != NULL) pGraph->Release();
if (pPropBag != NULL) pPropBag->Release();
if (pMoniker != NULL) pMoniker->Release();
if (pEnum != NULL) pEnum->Release();
if (pDevEnum != NULL) pDevEnum->Release();
if (pPin != NULL) pPin->Release();
if (pAMVidControl != NULL) pAMVidControl->Release();
if (pAMVCamControl != NULL) pAMVCamControl->Release();
CoUninitialize();
// Exit the program
exit(error);
}
class SampleGrabberCallback : public ISampleGrabberCB
{
public:
// Fake referance counting.
STDMETHODIMP_(ULONG) AddRef() { return 1; }
STDMETHODIMP_(ULONG) Release() { return 2; }
char filename[100];
STDMETHODIMP QueryInterface(REFIID riid, void **ppvObject)
{
if (NULL == ppvObject) return E_POINTER;
if (riid == __uuidof(IUnknown))
{
*ppvObject = static_cast<IUnknown*>(this);
return S_OK;
}
if (riid == __uuidof(ISampleGrabberCB))
{
*ppvObject = static_cast<ISampleGrabberCB*>(this);
return S_OK;
}
return E_NOTIMPL;
}
STDMETHODIMP SampleCB(double Time, IMediaSample *pSample)
{
fprintf(stderr, "Callback triggered SampleCB\n");
return E_NOTIMPL;
}
STDMETHODIMP BufferCB(double Time, BYTE *pBuffer, long BufferLen)
{
if ((g_StillMediaType.majortype != MEDIATYPE_Video) ||
(g_StillMediaType.formattype != FORMAT_VideoInfo) ||
(g_StillMediaType.cbFormat < sizeof(VIDEOINFOHEADER)) ||
(g_StillMediaType.pbFormat == NULL) ||
(g_StillMediaType.subtype != MEDIASUBTYPE_RGB24)
)
{
return VFW_E_INVALIDMEDIATYPE;
}
fprintf(stderr, "Save file\n");
sprintf(filename, "still/Image_Still_%d.bmp", img_index);
img_index++;
HANDLE hf = CreateFile(filename, GENERIC_WRITE,
FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, 0, NULL);
if (hf == INVALID_HANDLE_VALUE)
{
return E_FAIL;
}
long cbBitmapInfoSize = g_StillMediaType.cbFormat - SIZE_PREHEADER;
VIDEOINFOHEADER *pVideoHeader =
(VIDEOINFOHEADER*)g_StillMediaType.pbFormat;
BITMAPFILEHEADER bfh;
ZeroMemory(&bfh, sizeof(bfh));
bfh.bfType = 'MB'; // Little-endian for "BM".
bfh.bfSize = sizeof( bfh ) + BufferLen + cbBitmapInfoSize;
bfh.bfOffBits = sizeof( BITMAPFILEHEADER ) + cbBitmapInfoSize;
// Write the file header.
DWORD dwWritten = 0;
WriteFile( hf, &bfh, sizeof( bfh ), &dwWritten, NULL );
WriteFile(hf, HEADER(pVideoHeader), cbBitmapInfoSize, &dwWritten, NULL);
WriteFile( hf, pBuffer, BufferLen, &dwWritten, NULL );
CloseHandle( hf );
return S_OK;
}
};
// Global instance of the class.
SampleGrabberCallback g_StillCapCB;
int main(int argc, char **argv)
{
// Capture settings
int show_preview_window = 0;
int device_number = 2;
char device_name[100];
// Other variables
char char_buffer[100];
// Parse command line arguments. Available options:
// /preview
int n = 1;
while (n < argc)
{
// Process next command line argument
if (strcmp(argv[n], "/preview") == 0)
{
// Enable preview window
show_preview_window = 1;
}
else
{
// Unknown command line argument
fprintf(stderr, "Unrecognised option: %s\n", argv[n]);
exit_message("", 1);
}
// Increment command line argument counter
n++;
}
// Intialise COM
hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);
if (hr != S_OK)
exit_message("Could not initialise COM", 1);
// Create filter graph
hr = CoCreateInstance(CLSID_FilterGraph, NULL,
CLSCTX_INPROC_SERVER, IID_IGraphBuilder,
(void**)&pGraph);
if (hr != S_OK)
exit_message("Could not create filter graph", 1);
// Create capture graph builder.
hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL,
CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2,
(void **)&pBuilder);
if (hr != S_OK)
exit_message("Could not create capture graph builder", 1);
// Attach capture graph builder to graph
hr = pBuilder->SetFiltergraph(pGraph);
if (hr != S_OK)
exit_message("Could not attach capture graph builder to graph", 1);
// Create system device enumerator
hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL,
CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pDevEnum));
if (hr != S_OK)
exit_message("Could not crerate system device enumerator", 1);
// Video input device enumerator
hr = pDevEnum->CreateClassEnumerator(
CLSID_VideoInputDeviceCategory, &pEnum, 0);
if (hr != S_OK)
exit_message("No video devices found", 1);
// Get moniker for specified video input device,
// or for the first device if no device number
// was specified.
VARIANT var;
n = 0;
while(1)
{
// Access next device
hr = pEnum->Next(1, &pMoniker, NULL);
if (hr == S_OK)
{
n++; // increment device count
}
else
{
if (device_number == 0)
{
fprintf(stderr,
"Video capture device %s not found\n",
device_name);
}
else
{
fprintf(stderr,
"Video capture device %d not found\n",
device_number);
}
exit_message("", 1);
}
if (n >= device_number)
{
break;
}
}
// Get video input device name
hr = pMoniker->BindToStorage(0, 0, IID_PPV_ARGS(&pPropBag));
VariantInit(&var);
hr = pPropBag->Read(L"FriendlyName", &var, 0);
fprintf(stderr, "Capture device: %ls\n", var.bstrVal);
VariantClear(&var);
// Create capture filter and add to graph
hr = pMoniker->BindToObject(0, 0,
IID_IBaseFilter, (void**)&pCap);
if (hr != S_OK) exit_message("Could not create capture filter", 1);
// Add capture filter to graph
hr = pGraph->AddFilter(pCap, L"Capture Filter");
if (hr != S_OK) exit_message("Could not add capture filter to graph", 1);
// Create sample grabber filter
hr = CoCreateInstance(CLSID_SampleGrabber, NULL,
CLSCTX_INPROC_SERVER, IID_IBaseFilter,
(void**)&pSampleGrabberFilter);
if (hr != S_OK)
exit_message("Could not create Sample Grabber filter", 1);
// Query the ISampleGrabber interface of the sample grabber filter
hr = pSampleGrabberFilter->QueryInterface(
IID_ISampleGrabber, (void**)&pSampleGrabber);
if (hr != S_OK)
exit_message("Could not get ISampleGrabber interface to sample grabber filter", 1);
// Enable sample buffering in the sample grabber filter
hr = pSampleGrabber->SetBufferSamples(TRUE);
if (hr != S_OK)
exit_message("Could not enable sample buffering in the sample grabber", 1);
AM_MEDIA_TYPE mt;
ZeroMemory(&mt, sizeof(AM_MEDIA_TYPE));
mt.majortype = MEDIATYPE_Video;
mt.subtype = MEDIASUBTYPE_RGB24;
// Set media type in sample grabber filter
hr = pSampleGrabber->SetMediaType(&mt);
if (hr != S_OK)
exit_message("Could not set media type in sample grabber", 1);
// Add sample grabber filter to filter graph
hr = pGraph->AddFilter(pSampleGrabberFilter, L"SampleGrab");
if (hr != S_OK)
exit_message("Could not add Sample Grabber to filter graph", 1);
// Create Null Renderer filter
hr = CoCreateInstance(CLSID_NullRenderer, NULL,
CLSCTX_INPROC_SERVER, IID_IBaseFilter,
(void**)&pNullRenderer);
if (hr != S_OK)
exit_message("Could not create Null Renderer filter", 1);
// Add Null Renderer filter to filter graph
hr = pGraph->AddFilter(pNullRenderer, L"NullRender");
if (hr != S_OK)
exit_message("Could not add Null Renderer to filter graph", 1);
// Connect up the filter graph's capture stream
hr = pBuilder->RenderStream(
&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video,
pCap, pSampleGrabberFilter, pNullRenderer);
if (hr != S_OK)
exit_message("Could not render capture video stream", 1);
// Connect up the filter graph's preview stream
if (show_preview_window > 0)
{
hr = pBuilder->RenderStream(
&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,
pCap, NULL, NULL);
if (hr != S_OK && hr != VFW_S_NOPREVIEWPIN)
exit_message("Could not render preview video stream", 1);
}
// ------------STILL-IMAGE-CAPTURE-SETUP---------------
// Create sample grabber still filter
hr = CoCreateInstance(CLSID_SampleGrabber, NULL,
CLSCTX_INPROC_SERVER, IID_IBaseFilter,
(void**)&pSampleGrabberStillFilter);
if (hr != S_OK)
exit_message("Could not create Sample Grabber filter", 1);
// Add sample grabber filter to filter graph for still
hr = pGraph->AddFilter(pSampleGrabberStillFilter, L"SampleGrabStill");
if (hr != S_OK)
exit_message("Could not add Sample Grabber to filter graph still", 1);
// Create Null Render filter for still
hr = CoCreateInstance(CLSID_NullRenderer, NULL,
CLSCTX_INPROC_SERVER, IID_IBaseFilter,
(void**)&pNullRendererStill);
if (hr != S_OK)
exit_message("Could not create Null Renderer filter", 1);
// Add Null Renderer filter to filter graph for still
hr = pGraph->AddFilter(pNullRendererStill, L"NullRender Still");
if (hr != S_OK)
exit_message("Could not add Null Renderer to filter graph", 1);
// Query the ISampleGrabber interface of the sample grabber filter
hr = pSampleGrabberStillFilter->QueryInterface(
IID_ISampleGrabber, (void**)&pSampleGrabberStill);
if (hr != S_OK)
exit_message("Could not get ISampleGrabber interface to sample grabber filter", 1);
//Set media type for Still sample grabber
hr = pSampleGrabberStill->SetMediaType(&mt);
if (hr != S_OK)
exit_message("Could not set media type in sample grabber", 1);
// Connect up the filter graph's capture stream
hr = pBuilder->RenderStream(
&PIN_CATEGORY_STILL, &MEDIATYPE_Video,
pCap, pSampleGrabberStillFilter, pNullRendererStill);
if (hr != S_OK)
exit_message("Could not render capture video stream still", 1);
// Enable sample buffering in the sample grabber filter
hr = pSampleGrabberStill->SetOneShot(FALSE);
if (hr != S_OK)
exit_message("Set oneshot to false for sample", 1);
// Enable sample buffering in the sample grabber filter
hr = pSampleGrabberStill->SetBufferSamples(TRUE);
if (hr != S_OK)
exit_message("Could not enable sample buffering in the sample grabber", 1);
hr = pSampleGrabberStill->SetCallback(&g_StillCapCB, 1);
if (hr != S_OK)
exit_message("Could not set sample grabber callback", 1);
// Get media control interfaces to graph builder object
hr = pGraph->QueryInterface(IID_IMediaControl,
(void**)&pMediaControl);
if (hr != S_OK) exit_message("Could not get media control interface", 1);
// Run graph
while(1)
{
hr = pMediaControl->Run();
// Hopefully, the return value was S_OK or S_FALSE
if (hr == S_OK) break; // graph is now running
if (hr == S_FALSE) continue; // graph still preparing to run
// If the Run function returned something else,
// there must be a problem
fprintf(stderr, "Error: %u\n", hr);
exit_message("Could not run filter graph", 1);
}
// Query the capture filter for IAMVideoControl
hr = pCap->QueryInterface(IID_IAMVideoControl, (void**)&pAMVidControl);
if (hr != S_OK) exit_message("Could not get IAMVideoControl", 1);
// Query the capture filter for IAMCameraControl
hr = pCap->QueryInterface(IID_IAMCameraControl, (void**)&pAMVCamControl);
if (hr != S_OK) exit_message("Could not get IAMCameraControl", 1);
long Min, Max, Step, Default, Flags, Val;
// Get the range and default value.
hr = pAMVCamControl->GetRange(CameraControl_Exposure, &Min, &Max, &Step,
&Default, &Flags);
// Set Default exposure
hr = pAMVCamControl->Set(CameraControl_Exposure, Default, CameraControl_Flags_Manual);
if (hr != S_OK) exit_message("Could not set exposure", 1);
hr = pAMVCamControl->Get(CameraControl_Exposure, &Val, &Flags);
if (hr != S_OK) exit_message("Could not get current camera exposure", 1);
hr = pBuilder->FindPin(pCap, PINDIR_OUTPUT, &PIN_CATEGORY_STILL, NULL, FALSE, 0, &pPin);
if (hr != S_OK) exit_message("Could not get Pin of category StillImage", 1);
fprintf(stderr, "Found Pin\n");
// Get the media type from the stillsample grabber filter
hr = pSampleGrabberStill->GetConnectedMediaType(
&g_StillMediaType);
if (hr != S_OK) exit_message("Could not get media type", 1);
int count = 0;
// Loop to change exposure and capture still image
while(true)
{
fprintf(stderr, "Image = %d\n", count);
if(count == 30)
{
break;
}
if(count == 10)
{
hr = pAMVidControl->SetMode(pPin, VideoControlFlag_Trigger);
if (hr != S_OK) exit_message("Could not set mode trigger", 1);
pPin->Release();
}
if(count == 20)
{
fprintf(stderr, "Set New expo\n");
Val = -11;
Flags = CameraControl_Flags_Manual;
hr = pAMVCamControl->Set(CameraControl_Exposure, Val, Flags);
if (hr != S_OK) exit_message("Could not set exposure", 1);
}
count++;
hr = pAMVCamControl->Get(CameraControl_Exposure, &Val, &Flags);
if (hr != S_OK) exit_message("Could not get exposure", 1);
fprintf(stderr, "Expo Val: %ld\n", Val);
fprintf(stderr, "Expo Flags: %ld\n", Flags);
Sleep(500);
}
// Stop the graph
pMediaControl->Stop();
// Clean up and exit
exit_message("", 0);
}
This was the right way to do this. It turned out to be a hardware problem and was fixed by switching to a different camera.