[英]How to use stbi_write_png to write image pixel data to a png file
所以我在一个周末一直在跟踪光线追踪,最初是将所有像素数据写入 ppm 文件,并且只是在尝试写入不同的图像文件格式。 在互联网上的一些帮助下,我能够写入 bmp 文件,目前我正在尝试将像素数据写入 png。 我一直在尝试使用 stbi_write_png function 但创建的结果图像与所需的完全不同
我将在下面详细说明 bmp 部分和 png 以及生成的图像以及这两种实现的代码。
这是bmp写入的代码
#include<iostream>
#include<stdint.h>
#include<fstream>
#include<random>
#include "hitableList.h"
#include "sphere.h"
#include "camera.h"
#include "material.h"
#include <float.h> //for float_MAX
#include "main.h" //contains our typedef declarations, #defines and struct declarations.
typedef uint8_t u8;
typedef uint16_t u16;
typedef uint32_t u32;
typedef uint64_t u64;
typedef int8_t s8;
typedef int16_t s16;
typedef int32_t s32;
typedef int64_t s64;
typedef float f32;
#define STBI_MSC_SECURE_CRT
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"
#define CHANNEL_NUM 3
internal u32 GetTotalPixelSize(image_32 Image)//take image_32 Image
{
u32 Result = Image.Width*Image.Height * sizeof(u32);
return(Result);
}
//Function defintion to allocate image size
internal image_32 AllocateImage(u32 width, u32 height)
{
image_32 Image = {};//create the image object and initialize it.
Image.Height = height;
Image.Width = width;
u32 OutputPixelSize = GetTotalPixelSize(Image);//old version of the code does this line->sizeof(u32)*image.Width*image.Height;
Image.Pixels = (u32*)malloc(OutputPixelSize);//main source of the initial nullpointer at main *Out.
return(Image);
}
internal void WriteImage(image_32 Image, const char* OutputFileName)
{
u32 OutputPixelSize = GetTotalPixelSize(Image);
bitmap_header Header = {};
Header.FileType = 0x4D42;
Header.FileSize = sizeof(Header) + OutputPixelSize;//Need to set it later
//Header.Reserved1;//These are reserved and set by the header itself
//Header.Reserved2;//These are reserved and set by the header itself
Header.BitmapOffset = sizeof(Header);
Header.Size = sizeof(Header) - 14;//also need to set the size of the pixels. Since the header is 50 bytes check wikipedia.
Header.Width = Image.Width;
Header.Height = Image.Height;
Header.Planes = 1;
Header.BitsPerPixel = 32;
Header.Compression = 0;
Header.SizeOfBitmap = OutputPixelSize;//writing bottom part first. Very Important.
Header.HorzResolution = 0;
Header.VertResolution = 0;
Header.ColorsUsed = 0;
Header.ColorsImportant = 0;
FILE *OutFile = fopen(OutputFileName, "wb");
if (OutFile)
{
fwrite(&Header, sizeof(Header), 1, OutFile);//we write it into the header
fwrite(Image.Pixels, OutputPixelSize, 1, OutFile);
fclose(OutFile);
}
else
{
fprintf(stderr, "[Error]Unable to write output file %s. \n", OutputFileName);
}
}
vec3 color(const ray& r, hitable *world, int depth)
{
hit_record rec;
if(world->hit(r, 0.001, FLT_MAX, rec)){
ray scattered;
vec3 attenuation;
if(depth <50 && rec.mat_ptr->scatter(r,rec,attenuation,scattered)){
return attenuation*color(scattered, world, depth+1);
}
else{
return vec3(0,0,0);
}
}
else{
vec3 unit_direction = unit_vector(r.direction());
float t = 0.5*(unit_direction.y() + 1.0);
return (1.0-t)*vec3(1.0, 1.0, 1.0) + t*vec3(0.5, 0.7, 1.0);
}
}
int main()
{
printf("Raycasting......");
/*
int nx=1280;
int ny =720;
*/
u32 ns = 10;
u32 width = 1280;
u32 height = 720;
hitable *list[5];
list[0] = new sphere(vec3(0,0,-1), 0.5, new lambertian(vec3(0.8, 0.3, 0.3)));
list[1] = new sphere(vec3(0,-100.5,-1), 100, new lambertian(vec3(0.8, 0.8, 0.0)));
list[2] = new sphere(vec3(1,0,-1), 0.5, new metal(vec3(0.8, 0.6, 0.2), 0.3));
list[3] = new sphere(vec3(-1,0,-1), 0.5, new dielectric(1.5));
list[4] = new sphere(vec3(-1,0,-1), -0.45, new dielectric(1.5));
hitable *world = new hitable_list(list,4);
camera cam;
//u32 *Out = Image.Pixels;
u8* pixels = new u8[width * height * CHANNEL_NUM];
u32 index =0;
for(u32 y=0 ; y<height; y++)
{
for(u32 x=0; x<width; x++)
{
vec3 col(0, 0, 0);
for(u32 s=0; s < ns; s++)
{
float u = float(x+drand48())/float(width);
float v = float(y+drand48())/float(height);
ray r = cam.get_ray(u, v);
vec3 p = r.point_at_parameter(2.0);
col = col + color(r, world, 0); //col returns a vec3
}
col/=float(ns);//average sampling per pixel
vec3 BMPColor = vec3(255*col); //getting bmp color values from raytraced image.
u32 BMPvalue = BGRPack4x8(BMPColor); //packing the bmp color into an integer to write to the bitmap image.
*Out++ = BMPvalue;
if((y%64) ==0)
{
printf("\rRaycasting row %d%%....",100*y / height);
fflush(stdout);
}
}
WriteImage(Image, "..\\data\\Hollow_Glass_Sphere.bmp");//getting the raytraced image plane on test.bmp.
printf("\nDone.....\n");
return 0;
}
#include<iostream>
#include<stdint.h>
#include<fstream>
#include<random>
#include "hitableList.h"
#include "sphere.h"
#include "camera.h"
#include "material.h"
#include <float.h> //for float_MAX
#include "main.h" //contains our typedef declarations, #defines and struct declarations.
typedef uint8_t u8;
typedef uint16_t u16;
typedef uint32_t u32;
typedef uint64_t u64;
typedef int8_t s8;
typedef int16_t s16;
typedef int32_t s32;
typedef int64_t s64;
typedef float f32;
#define STBI_MSC_SECURE_CRT
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"
#define CHANNEL_NUM 3
vec3 color(const ray& r, hitable *world, int depth)
{
hit_record rec;
if(world->hit(r, 0.001, FLT_MAX, rec)){
ray scattered;
vec3 attenuation;
if(depth <50 && rec.mat_ptr->scatter(r,rec,attenuation,scattered)){
return attenuation*color(scattered, world, depth+1);
}
else{
return vec3(0,0,0);
}
}
else{
vec3 unit_direction = unit_vector(r.direction());
float t = 0.5*(unit_direction.y() + 1.0);
return (1.0-t)*vec3(1.0, 1.0, 1.0) + t*vec3(0.5, 0.7, 1.0);
}
}
int main()
{
printf("Raycasting......");
/*
int nx=1280;
int ny =720;
*/
u32 ns = 10;
u32 width = 1280;
u32 height = 720;
hitable *list[5];
list[0] = new sphere(vec3(0,0,-1), 0.5, new lambertian(vec3(0.8, 0.3, 0.3)));
list[1] = new sphere(vec3(0,-100.5,-1), 100, new lambertian(vec3(0.8, 0.8, 0.0)));
list[2] = new sphere(vec3(1,0,-1), 0.5, new metal(vec3(0.8, 0.6, 0.2), 0.3));
list[3] = new sphere(vec3(-1,0,-1), 0.5, new dielectric(1.5));
list[4] = new sphere(vec3(-1,0,-1), -0.45, new dielectric(1.5));
hitable *world = new hitable_list(list,4);
camera cam;
//u32 *Out = Image.Pixels;
u8* pixels = new u8[width * height * CHANNEL_NUM];
u32 index =0;
for(u32 y=0 ; y<height; y++)
{
for(u32 x=0; x<width; x++)
{
vec3 col(0, 0, 0);
for(u32 s=0; s < ns; s++)
{
float u = float(x+drand48())/float(width);
float v = float(y+drand48())/float(height);
ray r = cam.get_ray(u, v);
vec3 p = r.point_at_parameter(2.0);
col = col + color(r, world, 0); //col returns a vec3
}
col/=float(ns);//average sampling per pixel
col = vec3( sqrt(col[0]), sqrt(col[1]), sqrt(col[2]));
int ir = int(255.99*col[0]);
int ig = int(255.99*col[1]);
int ib = int(255.99*col[2]);
pixels[++index] = ir;
pixels[++index] = ig;
pixels[++index] = ib;
if((y%64) ==0)
{
printf("\rRaycasting row %d%%....",100*y / height);
fflush(stdout);
}
}
stbi_write_png("testpng_4.png", width, height, CHANNEL_NUM, pixels, width*CHANNEL_NUM);
printf("\nDone.....\n");
return 0;
}
这是对应于 bmp 写入代码的 BMP 图像,基于我在周末书中的光线追踪中阅读和实现的内容,这是正确的所需图像
这是对应于 png 写入代码的 PNG 图像,看起来图像在 colors 和方向上翻转。 我已尝试调试此图像中可能存在的问题,但失败了。 想到的唯一想法是它是否是字节顺序问题。 如果有人能帮我解决 png 写入的这个问题,我会非常高兴,如果这是一个字节顺序问题,我怎么能 go 解决它。
这是从 RGB 转换为 BRG 时的 output:
for(u32 y=0; y < height; y++)
它应该是这样的:
for (u32 y = height - 1; y >= 0; y--)
ir、ig 和 ib 值是int
类型; 但是,像素缓冲区和stbi_write_png
function 的输入在您的情况下需要unsigned char,
u8
。 将它们乘以 255.9 可能会产生远高于 255 的值,您可以考虑将它们固定在 [0, 255] 之间,然后再将它们转换为unsigned char.
您可以在这里查阅类似的讨论: stb image write issue
尽管将像素顺序从 RGB 更改为 BRG 可以解决问题,但您可能还需要考虑为什么图像整体看起来更亮。 这很可能是因为对 col 值的sqrt
操作,这将返回比原始 col 值更高的值,因为col
是小数。 在多重采样中,将总和除以样本数就足够了。 如果这些不起作用,我会检查stbi_write_png
是否仍在写入 alpha 通道,或者您的观众将其中一个通道视为 alpha 通道,这是最不可能的。
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