I have a Mipi camera that captures frames and stores them into the struct buffer that you can see below. Once the frame is stored I want to convert it into a cv::Mat, the thing is that the Mat ends up looking like the first pic.
The var buf.index is just part of the V4L2 API, useful to understand which buffer I'm using.
//The structure where the data is stored
struct buffer{
void *start;
size_t length;
};
struct buffer *buffers;
//buffer->mat
cv::Mat im = cv::Mat(cv::Size(width, height), CV_8UC3, ((uint8_t*)buffers[buf.index].start));
At first I thought that the data might be corrupted but storing the image with lodepng results in a nice image without any distortion.
unsigned char* out_buf = (unsigned char*)malloc( width * height * 3);
for(int pix = 0; pix < width*height; ++pix) {
memcpy(out_buf + pix*3, ((uint8_t*)buffers[buf.index].start)+4*pix+1, 3);
}
lodepng_encode24_file(filename, out_buf, width, height);
I bet it's something really silly.
the picture you post has oddly colored pixels and the patterns look like there's more information than simply 24 bits per pixel.
after inspecting the data, it appears that V4L gives you four bytes per pixel, and the first byte is always 0xFF (let's call that X). further, the channel order seems to be XRGB.
create a cv::Mat using 8UC4 to contain the data.
to use the picture in OpenCV, you need BGR order. cv::split the received data into its four color planes which are X,R,G,B. use cv::merge to reassemble the B,G,R planes into a picture that OpenCV can handle, or reassemble into R,G,B to create a Mat for other purposes (that other library you seem to use).
How can I load RAW 16-bit grayscale image with FreeImage?
I have unsigned char* buffer with raw data. I know its dimensions in pixels and I know it is 16bit grayscale.
I'm trying to load it with
FIBITMAP* bmp = FreeImage_ConvertFromRawBits(buffer, 1000, 1506, 2000, 16, 0, 0, 0);
and get broken RGB888 image. It is unclear what color masks I should use for grayscale as it has only one channel.
After many experiments I found partially working solution with FreeImage_ConvertFromRawBitsEx:
FIBITMAP* bmp = FreeImage_ConvertFromRawBitsEx(true, buffer, FIT_UINT16, 1000, 1506, 2000, 16, 0xFFFF, 0xFFFF, 0xFFFF);
(thanks #1201ProgramAlarm for hint with masks).
In this way, FreeImage loads the data, but in some semi-custom format. Most of conversion and saving functions (tried: JPG, PNG, BMP, TIF) fail.
As I can't load data in native 16bit format, I preferred to convert it into 8bit grayscale
unsigned short* buffer = new unsigned short[1000 * 1506];
// load data
unsigned char* buffer2 = new unsigned char[1000 * 1506];
for (int i = 0; i < 1000 * 1506; i++)
buffer2[i] = (unsigned char)(buffer[i] / 256.f);
FIBITMAP* bmp = FreeImage_ConvertFromRawBits(buffer2, 1000, 1506, 1000, 8, 0xFF, 0xFF, 0xFF, true);
This is really not the best solution, I even don't want to mark it as right answer (will wait for something better). But after this the format will be convenient for FreeImage and it could save/convert data to whatever.
Concerning your issue: I have read this from their PDF documentation FreeImage1370.pdf:
FreeImage_ConvertFromRawBits
1 4 8 16 24 32
DLL_API FIBITMAP *DLL_CALLCONV FreeImage_ConvertFromRawBits(BYTE *bits, int width, int
height, int pitch, unsigned bpp, unsigned red_mask, unsigned green_mask, unsigned
blue_mask, BOOL topdown FI_DEFAULT(FALSE));
Converts a raw bitmap somewhere in memory to a FIBITMAP. The parameters in this
function are used to describe the raw bitmap. The first parameter is a pointer to the start of
the raw bits. The width and height parameter describe the size of the bitmap. The pitch
defines the total width of a scanline in the source bitmap, including padding bytes that may be
applied. The bpp parameter tells FreeImage what the bit depth of the bitmap is. The
red_mask, green_mask and blue_mask parameters tell FreeImage the bit-layout of the color
components in the bitmap. The last parameter, topdown, will store the bitmap top-left pixel
first when it is TRUE or bottom-left pixel first when it is FALSE.
When the source bitmap uses a 32-bit padding, you can calculate the pitch using the
following formula:
int pitch = ((((bpp * width) + 31) / 32) * 4);
In the code you are showing:
FIBITMAP* bmp = FreeImage_ConvertFromRawBits(buffer, 1000, 1506, 2000, 16, 0, 0, 0);
You have the appropriate FIBTMAP* return type, you pass in your buffer of raw bits. From there the 2nd & 3rd parameters which are the width & height: width = 1000, height = 1506 and the 4th parameter which is the pitch: pitch = 2000 (if the bitmap is using 32bit padding refer to the last note above), the 5th parameter will be the bit depth measured in bpp you have as bpp = 16, the next 3 parameters are for your RGB color masks. Here you label them all as being 0. The last parameter is a bool flag for the orientation of the image :
if (topdown == true ) {
stores top-left pixel first )
else {
bottom left pixel is stored first
}
in which you omit the value.
Without more code of how you are reading in the file, parsing the header information etc. to prepare your buffer it is hard to tell where else there may be an error or an issue, but from what you provided; I think you need to check the color channel masks for grayscale images.
EDIT - I found another PDF for FreeImage from standford.edu here that refers to an older version 3.13.1 however the function declaration - definition doesn't look like it has changed any and they provide examples for b FreeImage_ConvertToRawBits & Free_Image_ConvertFromRawBits:
// this code assumes there is a bitmap loaded and
// present in a variable called ‘dib’
// convert a bitmap to a 32-bit raw buffer (top-left pixel first)
// --------------------------------------------------------------
FIBITMAP *src = FreeImage_ConvertTo32Bits(dib);
FreeImage_Unload(dib);
// Allocate a raw buffer
int width = FreeImage_GetWidth(src);
int height = FreeImage_GetHeight(src);
int scan_width = FreeImage_GetPitch(src);
BYTE *bits = (BYTE*)malloc(height * scan_width);
// convert the bitmap to raw bits (top-left pixel first)
FreeImage_ConvertToRawBits(bits, src, scan_width, 32,
FI_RGBA_RED_MASK, FI_RGBA_GREEN_MASK, FI_RGBA_BLUE_MASK,
TRUE);
FreeImage_Unload(src);
// convert a 32-bit raw buffer (top-left pixel first) to a FIBITMAP
// ----------------------------------------------------------------
FIBITMAP *dst = FreeImage_ConvertFromRawBits(bits, width, height, scan_width,
32, FI_RGBA_RED_MASK, FI_RGBA_GREEN_MASK, FI_RGBA_BLUE_MASK, FALSE);
I think this should help you with your question about the bit masks for the color channels in a grayscale image.
You already mentioned the FreeImage_ConvertFromRawBitsEx() function, which was added at some point between FreeImage v3.8 and v3.17, but are you calling it correctly? I was able to use this function with 16-bit grayscale data:
int nBytesPerRow = nWidth * 2;
int nBitsPerPixel = 16;
FIBITMAP* pFIB = FreeImage_ConvertFromRawBitsEx(TRUE, pImageData, FIT_UINT16, nWidth, nHeight, nBytesPerRow, nBitsPerPixel, 0, 0, 0, TRUE);
Note that nBytesPerRow and nBitsPerPixel have to be specified correctly for the 16-bit data. Also, I believe the color mask parameters are irrelevant for this data, since it is monochrome.
EDIT: I noticed that you said that saving the 16-bit data did not work correctly. That may be due to the file formats themselves. The only file format that I have found to be compatible with 16-bit grayscale data is TIFF. So, if you have 16-bit grayscale data, you can save a TIFF with FreeImage_Save() but you cannot save a BMP.
I have problem. When I'm loading mat from byte array there is a big problem; extra bytes cause mat to load wrong. If I send byte array ( width: 4-8-12-16-20 etc) It's not a problem because width and stride is equal. But If I byte array with extra stride bytes Image is corrupted. Is there a way to make it right ?
Function that I'm using:
Mat bytesToMat(byte * bytes,int height,int width)
{
Mat image = Mat(height,width,CV_8UC3,bytes).clone(); // make a copy
return image;
}
Example)
23 width image loaded as:
24 width image loaded (Correctly):
The link format was messed up in the comment, so I'll write an answer.
See the constructor step and steps parameters in the documentation. It lets you tell OpenCV how many bytes are in each row (including padding).
You'll also have to check if the byte array you're using as input has any added padding.
I have a few grayscale 8-bit images of size 450*450 px. How many bytes should be in data in this case? I guess that is 202500, but QImage's method byteCount() gives me 203400. Why?
QImage tmp(fname);
tmp.convertToFormat(QImage::Format_Indexed8);//it's not necessary
int W=tmp.width();//450
int H=tmp.height();//450
int ImgSize=tmp.byteCount();//203400
It seems like Image has 452*450 size.
I'm confused about the way libjpeg jpeg_read_scanlines works. It's my understanding that it decompresses a JPEG, row by row, and creates a decompressed pixel buffer.
Typical usage is something like:
jpeg_decompress_struct cinfo;
...
unsigned char* image = new unsigned char[cinfo.image_width * cinfo.image_height];
unsigned char* ptr = image;
int row_stride = cinfo.image_width;
while (cinfo.output_scanline < cinfo.image_height)
{
jpeg_read_scanlines(&cinfo, &ptr, 1);
ptr += row_stride;
}
Question: I'm confused about the output buffer size. In all example code I see which uses jpeg_read_scanlines, the size of the output buffer is width X height, where width and height refer to the dimensions of the JPEG file. So for a 10x10 JPEG file we'd have a 100 byte output buffer.
But... isn't the size of each RGB pixel 3 bytes (24-bit)? So shouldn't the uncompressed data actually be width X height X 3 bytes?
Why isn't it?
I notice that with code which uses jpeg_write_scanlines, the buffer to be compressed IS width X height X 3. So why is the buffer used with jpeg_read_scanlines only width X height?
You are only reading 1 line at a time with the line
jpeg_read_scanlines(&cinfo, &ptr, 1);
so you only needed the line
unsigned char* image = new unsigned char[cinfo.image_width * cinfo.image_height];
to be
unsigned char* image = new unsigned char[cinfo.image_width * cinfo.image_components];
The start of the buffer is being re-used for every scanline. Most of your current buffer is actually unused.
For RGB data, output_components will be 3 (R,G,B).
Here's some related documentation from libjpeg.txt:
output_width image width and height, as scaled
output_height
out_color_components # of color components in out_color_space
output_components # of color components returned per pixel
colormap the selected colormap, if any
actual_number_of_colors number of entries in colormap
output_components is 1 (a colormap index) when quantizing colors; otherwise it
equals out_color_components. It is the number of JSAMPLE values that will be
emitted per pixel in the output arrays.
Typically you will need to allocate data buffers to hold the incoming image.
You will need output_width * output_components JSAMPLEs per scanline in your
output buffer, and a total of output_height scanlines will be returned.