Re: [dev] Looking for simple, alpha supporting image format

[Charlie Murphy]

FRIGN wrote:
> The writing-function is rather trivial.
> Now, what puzzles me is why no explanation is given on how the data
> itself should be stored. It says RGBA, so I suppose he meant

Thanks for the feedback.  The header is strict to avoid complex text
handling.  I have attached a script to convert any image to this format,
using ImageMagick.

Revised spec
------------

This is an easy-to-parse image format that works well in pipelines.
Inspired by Netpbm and the Plan 9 image format.

Bytes   Description
9       ASCII string: "imagefile"
1       Any byte.
9       Right-justified, blank-padded ASCII string containing the width.
1       Any byte.
9       Right-justified, blank-padded ASCII string containing the height.
1       Any byte.

Then, (width*height) pixels, where each pixel is four bytes.  Each byte
represents red, green, blue, and alpha respectively.  The X axis runs
fastest.

This function reads an image:

        char *
        readimage(int fd, int *w, int *h)
        {
                char hdr[30];
                char *data;
                int len;
                
                if (read(fd, hdr, 30) != 30)
                        return NULL;
                
                hdr[9] = '\0';
                hdr[19] = '\0';
                hdr[29] = '\0';
                
                if (strcmp(hdr, "imagefile") != 0)
                        return NULL;
                
                *w = atoi(hdr+10);
                *h = atoi(hdr+20);
                len = *w * *h * 4;
                
                data = malloc(len);
                if (!data)
                        return NULL;
                
                if (read(fd, data, len) != len) {
                        free(data);
                        return NULL;
                }

                return data;
        }

This function writes an image:

        int
        writeimage(int fd, int w, int h, char *data)
        {
                char hdr[30];
                
                if (snprintf(hdr, 30, "imagefile %9d %9d ", w, h) != 30)
                        return -1;
                if (write(fd, hdr, 30) != 30)
                        return -1;
                if (write(fd, data, w*h*4) != w*h*4)
                        return -1;
                
                return 0;
        }

imagefile.sh
Description: Bourne shell script