apps: cam: Add support for PPM output format

When file output is requested from cam app, it simply dumps the
processed data and it must be converted to a readable image format
manually. Let's add support for PPM output file format to make files
produced by cam directly readable by image display and processing
software.

For now, only BGR888 output format, which is the simplest one to use, is
supported but nothing prevents adding support for other output formats
if needed. Nevertheless, they would typically need byte reordering or
other conversions for PPM file format. It may be better to find a way to
dump the image data in other output formats directly using some of the
already existing file formats or raw file format converters.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/apps/cam/file_sink.cpp

@@ -17,6 +17,7 @@
 
 #include "../common/dng_writer.h"
 #include "../common/image.h"
+#include "../common/ppm_writer.h"
 
 #include "file_sink.h"
 
@@ -76,6 +77,7 @@ void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
 #ifdef HAVE_TIFF
 	bool dng = filename.find(".dng", filename.size() - 4) != std::string::npos;
 #endif /* HAVE_TIFF */
+	bool ppm = filename.find(".ppm", filename.size() - 4) != std::string::npos;
 
 	if (filename.empty() || filename.back() == '/')
 		filename += "frame-#.bin";
@@ -102,6 +104,15 @@ void FileSink::writeBuffer(const Stream *stream, FrameBuffer *buffer,
 		return;
 	}
 #endif /* HAVE_TIFF */
+	if (ppm) {
+		ret = PPMWriter::write(filename.c_str(), stream->configuration(),
+				       image->data(0));
+		if (ret < 0)
+			std::cerr << "failed to write PPM file `" << filename
+				  << "'" << std::endl;
+
+		return;
+	}
 
 	fd = open(filename.c_str(), O_CREAT | O_WRONLY |
 		  (pos == std::string::npos ? O_APPEND : O_TRUNC),

src/apps/cam/main.cpp

@@ -154,6 +154,8 @@ int CamApp::parseOptions(int argc, char *argv[])
 			 "If the file name ends with '.dng', then the frame will be written to\n"
 			 "the output file(s) in DNG format.\n"
 #endif
+			 "If the file name ends with '.ppm', then the frame will be written to\n"
+			 "the output file(s) in PPM format.\n"
 			 "The default file name is 'frame-#.bin'.",
 			 "file", ArgumentOptional, "filename", false,
 			 OptCamera);

src/apps/common/meson.build

@@ -3,6 +3,7 @@
 apps_sources = files([
     'image.cpp',
     'options.cpp',
+    'ppm_writer.cpp',
     'stream_options.cpp',
 ])
 

src/apps/common/ppm_writer.cpp

@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024 Red Hat, Inc.
+ *
+ * ppm_writer.cpp - PPM writer
+ */
+
+#include "ppm_writer.h"
+
+#include <fstream>
+#include <iostream>
+
+#include <libcamera/formats.h>
+#include <libcamera/pixel_format.h>
+
+using namespace libcamera;
+
+int PPMWriter::write(const char *filename,
+		     const StreamConfiguration &config,
+		     const Span<uint8_t> &data)
+{
+	if (config.pixelFormat != formats::BGR888) {
+		std::cerr << "Only BGR888 output pixel format is supported ("
+			  << config.pixelFormat << " requested)" << std::endl;
+		return -EINVAL;
+	}
+
+	std::ofstream output(filename, std::ios::binary);
+	if (!output) {
+		std::cerr << "Failed to open ppm file: " << filename << std::endl;
+		return -EINVAL;
+	}
+
+	output << "P6" << std::endl
+	       << config.size.width << " " << config.size.height << std::endl
+	       << "255" << std::endl;
+	if (!output) {
+		std::cerr << "Failed to write the file header" << std::endl;
+		return -EINVAL;
+	}
+
+	const unsigned int rowLength = config.size.width * 3;
+	const char *row = reinterpret_cast<const char *>(data.data());
+	for (unsigned int y = 0; y < config.size.height; y++, row += config.stride) {
+		output.write(row, rowLength);
+		if (!output) {
+			std::cerr << "Failed to write image data at row " << y << std::endl;
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}

src/apps/common/ppm_writer.h

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Red Hat, Inc.
+ *
+ * ppm_writer.h - PPM writer
+ */
+
+#pragma once
+
+#include <libcamera/base/span.h>
+
+#include <libcamera/stream.h>
+
+class PPMWriter
+{
+public:
+	static int write(const char *filename,
+			 const libcamera::StreamConfiguration &config,
+			 const libcamera::Span<uint8_t> &data);
+};