How to compress image on linux? - c++

Question

I am writing function to compress image using GDI+ on windows, and it's working well,
void ImageProcessorImpl::compressImpl(const std::string& path, int size, UInt8 quality)
{
HBITMAP hbmReturn = NULL;
Bitmap* bmPhoto = NULL;
std::wstring upath;
UnicodeConverter::toUTF16(path, upath);
// make source file close automatically, Bitmap detructor will be called
{
Bitmap image(upath.c_str());
int srcWidth = image.GetWidth();
int srcHeight = image.GetHeight();
float percent = 0;
int destX = 0, destY = 0;
if (srcWidth > srcHeight)
{
percent = ((float)size/(float)srcWidth);
destX = (int)((size - (srcWidth * percent))/2);
}
else
{
percent = ((float)size/(float)srcHeight);
destY = (int)((size - (srcHeight * percent))/2);
}
if (percent >= 1.0f)
return; // skip compress
int destWidth = (int)(srcWidth * percent);
int destHeight = (int)(srcHeight * percent);
bmPhoto = new Bitmap(destWidth, destHeight, PixelFormat24bppRGB);
bmPhoto->SetResolution(image.GetHorizontalResolution(), image.GetVerticalResolution());
Graphics *grPhoto = Graphics::FromImage(bmPhoto);
Color colorW(255, 255, 255, 255);
grPhoto->Clear(colorW);
grPhoto->SetInterpolationMode(InterpolationModeHighQualityBicubic);
grPhoto->DrawImage(&image, Rect(destX, destY, destWidth, destHeight));
bmPhoto->GetHBITMAP(colorW, &hbmReturn);
delete grPhoto;
} // end source image file, Bitmap image(upath.c_str());
// find appropriate encoder, jpeg
CLSID encoderClsid;
getEncoderClsid(L"image/jpeg", &encoderClsid);
// set output quality for jpeg alone
EncoderParameters encoderParameters;
setEncoderQuality(&encoderParameters, &quality);
// output to image file with desired quality
bmPhoto->Save(upath.c_str(), &encoderClsid, &encoderParameters);
// release resources
delete bmPhoto;
DeleteObject(hbmReturn);
}
int ImageProcessorImpl::getEncoderClsid(const WCHAR* format, void* clsid)
{
UINT num = 0; // number of image encoders
UINT size = 0; // size of the image encoder array in bytes
ImageCodecInfo* pImageCodecInfo = NULL;
GetImageEncodersSize(&num, &size);
if(size == 0)
return -1; // Failure
pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
if(pImageCodecInfo == NULL)
return -1; // Failure
GetImageEncoders(num, size, pImageCodecInfo);
for (UINT j = 0; j < num; ++j)
{
if (wcscmp(pImageCodecInfo[j].MimeType, format) == 0)
{
*(CLSID*)clsid = pImageCodecInfo[j].Clsid;
free(pImageCodecInfo);
return j; //Success
}
}
free(pImageCodecInfo);
return -1; // Failure
}
void ImageProcessorImpl::setEncoderQuality(void* params, UInt8* quality)
{
EncoderParameters* encoderParams = (EncoderParameters*)params;
encoderParams->Count = 1;
encoderParams->Parameter[0].Guid = EncoderQuality;
encoderParams->Parameter[0].Type = EncoderParameterValueTypeLong;
encoderParams->Parameter[0].NumberOfValues = 1;
encoderParams->Parameter[0].Value = quality;
}
But, I want to have this function on linux, I don't know what lib I can use to implement such function on linux, who can help me?
Thnx

Answer 1

You can use the ImageMagick library or netpbm library. Netpbm also has command line tools to manipulate images.

Answer 2

OpenCV provides an easy to use interface for all types of image processing as well as simple things such as image compression. It may be a bit of an overkill for image compression only, but I suppose it may helpful if you plan on doing other things with these images.