How to convert/set bit depth from 1 to 8 bit

[ademmler]

How can I set / convert 1bit BW images to 8Bit Greyscale using libvips and c++.

[jcupitt]

Just set bitdepth, eg.:

$ vips copy mono.png x.tif[bitdepth=1]
$ tiffinfo x.tif
TIFF Directory at offset 0x372744 (5b008)
  Image Width: 1450 Image Length: 2048
  Resolution: 28.35, 28.35 pixels/cm
  Bits/Sample: 1
  Sample Format: unsigned integer
  Compression Scheme: None
  Photometric Interpretation: min-is-black
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 1
  Rows/Strip: 128
  Planar Configuration: single image plane
$ 

Same for PNG and GIF.

[ademmler]

Ok I see - because the final step is to go to the display RGB profile (for best viewing result) I will try to use L-Star in-between (as a calibrated colorspace). I guess I can do the final conversion also in vips.
Have I understood correctly - that you use LCMS inside vips for all ICC stuff?

[jcupitt]

It's a mix, but lcms is used for conversions using profiles.

[ademmler]

Seems like conversion from sRGB to other RGB is not possible - I get this error:
(process:3241): VIPS-WARNING **: 15:10:02.420: profile incompatible with image

merged = VImage::composite({rgb_layers, sp1_layers, sp2_layers},
        {VIPS_BLEND_MODE_MULTIPLY, VIPS_BLEND_MODE_MULTIPLY});			

VImage final_image = merged.icc_transform("LStar-RGB.ICC");

[jcupitt]

It should work. Convert the CMYK to lstar, eg.:

// compile with:
//
//   g++ -std=c++11 -g -Wall -o recombine-rgb recombine_rgb.cpp `pkg-config vips-cpp --cflags --libs`

#include <stdlib.h>
#include <vips/vips8>

using namespace vips;

VImage
vopen(const char *filename)
{
    const VipsAccess access = VIPS_ACCESS_SEQUENTIAL;

    return VImage::new_from_file(filename, VImage::option()
            ->set ("access", access));
}

int
main( int argc, char **argv )
{
    if(VIPS_INIT(argv[0]))
        vips_error_exit(NULL);

    VImage c = vopen("testpage-Cyan.tif");
    VImage m = vopen("testpage-Magenta.tif");
    VImage y = vopen("testpage-Yellow.tif");
    VImage k = vopen("testpage-Black.tif");
    VImage spot1 = vopen("testpage-Spot1.tif");
    VImage spot2 = vopen("testpage-Spot2.tif");

    // Create CMYK image
    // these planes have white for no-ink, so we need to invert (cmyk uses 255
    // to mean lots of ink)
    VImage cmyk_layers = VImage::bandjoin({c, m, y, k})
        .copy(VImage::option()
            ->set("interpretation", VIPS_INTERPRETATION_CMYK))
        .invert();

    // to RGB
    VImage rgb_layers = cmyk_layers
        .icc_transform("LStar-RGB-v4.icc");

    // we have to invert the spot mask, since it uses 0 to mean lots of ink,
    // but rgb uses 0 to mean black
    VImage sp1_layers = rgb_layers
        .new_from_image({255, 255, 0})
        .bandjoin(spot1.invert());

    VImage sp2_layers = rgb_layers
        .new_from_image({255, 0, 255})
        .bandjoin(spot2.invert());

    //Merge all together
    VImage merged = VImage::composite({rgb_layers, sp1_layers, sp2_layers},
        {VIPS_BLEND_MODE_MULTIPLY, VIPS_BLEND_MODE_MULTIPLY});

    merged.write_to_file("merged.tif");

    return 0;
}

To generate:

The {255, 255, 0} are in lstar space.

[ademmler]

Hi - thank you for helping me with that again!
The honor is again for you - perfect support!

?How can I mark just your last part to be the full answer?

[ademmler]

Hi, I am back. I am trying to run my sample code with very large tiffs.
I reduce the example to CMYK colors only.

... shortened
VImage cmyk_layers = VImage::bandjoin({c, m, y, k})
.copy(VImage::option()
->set("interpretation", VIPS_INTERPRETATION_CMYK))
.invert();

cmyk_layers.write_to_file("möget.tif");
... shortend

I have 4 tiffs - one for each color - like this one.

TIFF Directory at offset 0x8 (8)
  Subfile Type: (0 = 0x0)
  Image Width: 116977 Image Length: 271560
  Resolution: 2400, 2400 pixels/inch
  Bits/Sample: 1
  Compression Scheme: LZW
  Photometric Interpretation: min-is-white
  Samples/Pixel: 1
  Rows/Strip: 229
  Planar Configuration: single image plane
  ImageDescription: Black
  Software: LnTIFF
  Tag 32781: 1. 631d1d9b-b1be-4a17-be9e-9fcf2bebb098.jdf (K)

The resulting tiff has this characteristics:

TIFF Directory at offset 0x1d95ab8130 (127065096496)
  Image Width: 116977 Image Length: 271560
  Resolution: 2400, 2400 pixels/inch
  Bits/Sample: 8
  Sample Format: unsigned integer
  Compression Scheme: None
  Photometric Interpretation: separated
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 4
  Rows/Strip: 128
  Planar Configuration: single image plane
  ImageDescription: Cyan
  InkSet: 1

1. The resulting image can't be opened or displayed by an image viewer like Photoshop.
   What should I change to get a more compatible tiff.

2. The size is immense (128 GB). Can I reduce the images on the fly or before merging?

3. How to speed up the whole process?

Regards Alexander

[jcupitt]

You can set LZW compression on the output image, perhaps:

    merged.write_to_file("merged.tif", VImage::option()
            ->set("compression", VIPS_FOREIGN_TIFF_COMPRESSION_LZW));

or equivalently:

    merged.write_to_file("merged.tif[compression=lzw]");

[jcupitt]

... you might need to set the bigtiff option as well.

[ademmler]

Hi, thx for your response and hint. I tried your suggestion together with downsampling.
But it is still extremely slow. What would be the best way - order- to downsample and convert to Standard 8bit CMYK?

#include <stdlib.h>
#include <vips/vips8>

using namespace vips;

int
main( int argc, char **argv )
{
    if(VIPS_INIT(argv[0]))
        vips_error_exit(NULL);
    
    //Load images
    VImage c = VImage::new_from_file("testpage(Cyan).tif",
                                     VImage::option()->set ("access", VIPS_ACCESS_SEQUENTIAL));
    VImage m = VImage::new_from_file("testpage(Magenta).tif",
                                     VImage::option()->set ("access", VIPS_ACCESS_SEQUENTIAL));
    VImage y = VImage::new_from_file("testpage(Yellow).tif",
                                     VImage::option()->set ("access", VIPS_ACCESS_SEQUENTIAL));
    VImage k = VImage::new_from_file("testpage(Black).tif",
                                     VImage::option()->set ("access", VIPS_ACCESS_SEQUENTIAL));
                                     
	//Reduce images
	c.resize(0.25);
	m.resize(0.25);
	y.resize(0.25);	
	k.resize(0.25);                                     
          
    //Create CMYK image
    VImage image = VImage::bandjoin({c, m, y, k})
            .copy(VImage::option()
                    ->set("interpretation", VIPS_INTERPRETATION_CMYK))
                    .invert();
        
	image.write_to_file("merged.tif", VImage::option()
            ->set("compression", VIPS_FOREIGN_TIFF_COMPRESSION_LZW)
            ->set("bigtiff", true)
            ->set("tile", true)
            ->set("pyramid", true)
            );
    
    return 0;
}

[jcupitt]

->set("compression", VIPS_FOREIGN_TIFF_COMPRESSION_LZW)

Unfortunately LZW compression in libtiff is both slow and single-threaded. You could try saving without compression -- the files will be uselessly large, but it might confirm where the bottleneck is.

You could also bandjoin before the resize, it should help a little.

[jcupitt]

And obviously you need:

c = c.resize(0.25)

I expect that was just a typo.

[jcupitt]

... so I would write:

    VImage c = VImage::new_from_file("testpage(Cyan).tif",
                                     VImage::option()->set ("access", "sequential"));
    VImage m = VImage::new_from_file("testpage(Magenta).tif",
                                     VImage::option()->set ("access", "sequential"));
    VImage y = VImage::new_from_file("testpage(Yellow).tif",
                                     VImage::option()->set ("access", "sequential"));
    VImage k = VImage::new_from_file("testpage(Black).tif",
                                     VImage::option()->set ("access", "sequential"));
          
    VImage image = VImage::bandjoin({c, m, y, k})
            .copy(VImage::option()->set("interpretation", "cmyk"))
            .resize(0.25)
            .invert();