问题描述
所以我编写了一个C ++程序，可以生成非常高分辨率的图片（分形）。
我使用fstream将所有数据保存在.ppm文件中。
So I wrote a C++ program that produces very high resolution pictures (fractals). I use fstream to save all the data in a .ppm file.
一切正常，但当我进入真正的高分辨率（38400x21600）ppm时文件有~8千兆字节。
然而，凭借我的16 GB Ram，我仍然无法转换那张照片。我下载了几个转换器，但他们无法处理它。当我试图导出为......时，甚至Gimp也崩溃了。
Everything works fine, but when I go into really high resolution (38400x21600) the ppm file has ~8 Gigabytes. With my 16 Gigabytes of Ram, however, I am still not able to convert that picture. I downloaded couple of converters, but they couldn't handle it. Even Gimp crashed when I try to "export as...".
那么，有没有人知道一个可以处理真正大ppm文件的好转换器？事实上，我甚至想要超过100千兆字节。我不在乎它是否很慢，它应该工作。
So, does anyone know a good converter that can handle really large ppm files? In fact, I even want to go above 100 Gigabytes. I don't care if it's slow, it should just work.
如果没有这样的转换器：有没有办法以更好的方式使用std :: ofstream？也许，是否有自动生成PNG文件的库？
If there is no such converter: Is there a way to std::ofstream in a better way? Like maybe, is there a library that automaticly produces a PNG file?
感谢您的帮助！
编辑：我也问自己，保存这些大图像的最佳格式是什么。我研究过，JPEG看起来很漂亮（体积小，质量还不错）。但是可能有更好的格式吗？让我知道。谢谢
also I asked myself what might be the best format for saving these large images. I researched and JPEG looks quite pretty (small size, still good quality). But may be there a better format? Let me know. Thanks
推荐答案
一些想法...
8- 38400x21600的位PPM文件应占用2.3GB。相同尺寸的16位PPM文件需要两倍，即4.6GB，所以我不确定你从哪里获得8GB。
An 8-bit PPM file of 38400x21600 should take 2.3GB. A 16-bit PPM file of the same dimensions requires twice as much, i.e. 4.6GB so I am not sure where you got 8GB from.
非常适合处理大型图像，如果我采用38400x21600 PPM文件，在终端中使用以下命令（即命令行），我可以看到它在58MB的RAM处达到峰值，从PPM转换为JPEG ...
VIPS is excellent for processing large images, and if I take a 38400x21600 PPM file, and use the following command in Terminal (i.e. at the command-line), I can see it peaks at 58MB of RAM to do the conversion from PPM to JPEG...
vips jpegsave fractal.ppm fractal.jpg --vips-leak
memory: high-water mark 58.13 MB
在一个合理的规格iMac上需要31秒，并从我的（随机）数据产生一个480MB的文件，所以你会期望你的结果要小得多，因为我很漂亮不可压缩。
That takes 31 seconds on a reasonable spec iMac and produces a 480MB file from my (random) data, so you would expect your result to be much smaller, since mine is pretty incompressible.
另一方面，ImageMagick需要1.1GB峰值工作内存并在74秒内完成相同的转换：
ImageMagick, on the other hand, takes 1.1GB peak working set of memory and does the same conversion in 74 seconds:
/usr/bin/time -l convert fractal.ppm fractal.jpg
73.81 real 69.46 user 4.16 sys
11616595968 maximum resident set size
0 average shared memory size
0 average unshared data size
0 average unshared stack size
4051124 page reclaims
4 page faults
0 swaps
0 block input operations
106 block output operations
0 messages sent
0 messages received
0 signals received
9 voluntary context switches
11791 involuntary context switches
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