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2004.04.04 17:22 "Re: 16 bit gray scale images and tiff", by Andrey Kiselev
Hi,
On Fri, Apr 02, 2004 at 09:05:31AM -0500, Wendel Dean Renner wrote:
> The TIFF 6.0 Specification, on page 22, says "Allowable values for
> Baseline TIFF grayscale images are 4 and 8, allowing either 16 or 256
> distinct shades of gray." Maybe the problem here is the word
> "Baseline". I don't know what that means.
Well, page 11 of the specification says: "Baseline TIFF is the core of
TIFF, the essentials that all mainstream TIFF developers should support
in their products." TIFF files can contain a lot of extra info used in
complex applications, but simple baseline files should be read by any
TIFF-aware applications, even by simple ones.
> Where in that document is 16 bits per sample allowed?
Look at the BitsPerSample tag description at the page 29.
> In any event I posted a message last week because I could not
> understand how film scanners could be writing 16 bit gray scale images
> in TIFF format (for x-ray film which is black and white)
I have attached a simple application to write 16-bit TIFF. Search
mailing list archives, I have posted sample code to read TIFF images
recently.
> I want to thank the two people who replied to me. To read a 16 bit
> gray scale I was told to call TIFFReadScanline in the TIFF library,
> and that works. For each pixel the first byte was the most
> significant byte.
>
> Do I assume that all images are of this byte order?
No. The byte order is specified in TIFF header and you will get the
properly swapped bytes from the library.
> Another question, is there such a thing as an RGB image with 16 bits
> per sample (and so 3 samples per pixel)?
Yes, and such images are widely used.
> What happens when a 14 bit scanner writes out a color image? Are
> they truncated to 8 bits per color?
That depends on how the scanner sofware writes image. I believe it
should be written in form of 16-bit files.
> I notice in the TIFF library that TIFFGetR, TIFFGetB and TIFFGetG
> assume RGB is 3 bytes, blue the most significant byte, and so byte
> order is also assumed besides the size of each sample.
Don't use TIFFGetR/G/B functions. They are part of the TIFFRGBAImage
interface which is designed for simple viewers and not suitable for your
needs.
> Lastly, I have a 16 bit TIFF gray scale image file written by Adobe
> PhotoShop that someone sent me, that TIFFOpen bombs on every time (I
> mean the program crashes upon calling TIFFOpen passing in the file
> name as an argument). Yet the image displays OK if I use some other
> image viewing software. But I have yet another 16 bit gray scale
> image from PhotoShop.that gets past TIFFOpen and I can read and
> display the image. I am using a Windows libtiff that I down loaded
> (I can't remember if it was from your site or someplace else). (I also
> run under Linux and have not tried it there yet.)
Please, try the latest libtiff package (3.6.1). If you still get an
error I shall try to fix the bug (but I shall need a sample image to
work).
Andrey
--
Andrey V. Kiselev
Home phone: +7 812 5274898 ICQ# 26871517
#include <stdio.h>
#include "tiffio.h"
#define XSIZE 256
#define YSIZE 256
int main (int argc, char **argv)
{
uint32 image_width, image_height;
float xres, yres;
uint16 spp, bpp, photo, res_unit;
TIFF *out;
int i, j;
uint16 array[XSIZE * YSIZE];
for (j = 0; j < YSIZE; j++)
for(i = 0; i < XSIZE; i++)
array[j * XSIZE + i] = i * j;
out = TIFFOpen("out.tif", "w");
if (!out)
{
fprintf (stderr, "Can't open %s for writing\n", argv[1]);
return 1;
}
image_width = XSIZE;
image_height = YSIZE;
spp = 1; /* Samples per pixel */
bpp = 16; /* Bits per sample */
photo = PHOTOMETRIC_MINISBLACK;
TIFFSetField(out, TIFFTAG_IMAGEWIDTH, image_width / spp);
TIFFSetField(out, TIFFTAG_BITSPERSAMPLE, bpp);
TIFFSetField(out, TIFFTAG_SAMPLESPERPIXEL, spp);
TIFFSetField(out, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG);
TIFFSetField(out, TIFFTAG_PHOTOMETRIC, photo);
TIFFSetField(out, TIFFTAG_ORIENTATION, ORIENTATION_BOTLEFT);
/* It is good to set resolutions too (but it is not nesessary) */
xres = yres = 100;
res_unit = RESUNIT_INCH;
TIFFSetField(out, TIFFTAG_XRESOLUTION, xres);
TIFFSetField(out, TIFFTAG_YRESOLUTION, yres);
TIFFSetField(out, TIFFTAG_RESOLUTIONUNIT, res_unit);
for (j = 0; j < image_height; j++)
TIFFWriteScanline(out, &array[j * image_width], j, 0);
TIFFClose(out);
return 0;
}