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

From: Markus Teich <markus.teich_AT_stusta.mhn.de>
Date: Wed, 16 Jul 2014 15:28:44 +0200

koneu wrote:
> If anything, I would store the numbers as unsigned 64 bit LSB and change the
> read/write functions for MSB architectures.

Heyho,

max(uint32_t) = 4.294.967.296 is already way more than the proposed max of
999.999.999. I would even suggest uint16_t is enough. To store images larger
than 65536^2 (=16GiB with 4 bytes per pixel) is far enough in the future and
also the argument with the need for greater color depth applies. We could just
use htons and ntohs then:

spec

----
Bytes	Description
9	ASCII string: "imagefile"
2	Width of the image stored in network byte order (big-endian)
2	Height of the image stored in network byte order (big-endian)
Then, (width*height) pixels arranged in height scanlines, where each pixel is
four bytes.  Each byte represents red, green, blue, and alpha respectively.
This function reads an image:
	char *
	readimage(int fd, uint16_t *w, uint16_t *h)
	{
		char hdr[13];
		char *data;
		int len;
		if (read(fd, hdr, 13) != 13 || strcmp(hdr, "imagefile"))
			return NULL;
		*w = ntohs(hdr[9]);
		*h = ntohs(hdr[11]);
		len = (*w) * (*h) * 4;
		if (!(data = malloc(len)) || read(fd, data, len) != len) {
			free(data);
			return NULL;
		}
		return data;
	}
This function writes an image:
	int
	writeimage(int fd, uint16_t w, uint16_t h, char *data)
	{
		uint16_t nw = htons(w);
		uint16_t nh = htons(h);
		return (write(fd, "imagefile", 9) == 9 &&
		        write(fd, &nw, 2) == 2 &&
		        write(fd, &nh, 2) == 2 &&
		        write(fd, data, w*h*4) == w*h*4);
	}
We also avoid *printf and stdio.h.
--Markus

Received on Wed Jul 16 2014 - 15:28:44 CEST