Setting the color depth on TIFF files written using the Wand API.

[emxjay]

The issue is well explained here.

Can you please clarify this for us?

[mikayla-grace]

Modern releases of ImageMagick, by default, writes to an image format @ the same depth as the source image assuming the particular image format supports the depth. XBM, for example, only supports images of depth 1, regardless of the source image depth. This is by design. If you find that ImageMagick behaves differently, post a command-line illustrating the exception.

[emxjay]

Hi - What do you mean by modern? For instance, the issue above is valid on ImageMagick 6.7.7-10 (which is, btw, shipped w/ the latest release of Ubuntu LTS).

[mikayla-grace]

When appending an image, the image depth is that of the first image. If your first image has a depth of 1, the output TIFF image has a depth of 1. We'll add a patch to fix this problem. In the mean-time, use setImageDepth(16) to ensure a depth of 16 bits-per-pixel. If it doesn't already, IMagick should also support setDepth(). setImageDepth() is specific to a particular image whereas setDepth() applies to all images in a sequence.

[Danack]

I've just seen that this is a duplicate (or at least caused by the same desire) of #66 .

Are you saying that setDepth() will always control the output image depth?

[emxjay]

@mikayla-grace setImageDepth(16) have no effect, unless setType() is specified. And that's the case for every image of the sequence (including the first one). And again, I'm talking about the Wand API, not the command-line tools.

[mikayla-grace]

Will setDepth() always control the output image depth? Well that depends on the output format. XBM, for example, is limited to a pixel depth of 1 so a setDepth(16) would still return an image of depth 1. ImageMagick typically sets the attributes of the destination image from the source image. Assume two images, the first of depth 1 and the second of depth 8. Write this to TIFF and the first image in the TIFF is of depth 1 and the second of depth 8. Whereas, if you call setDepth(8), both images in the TIFF file will be of depth 8.

setImageDepth() has no effect unless setType() is specified? We'll need a specific use case that we can download and reproduce the problem before we can comment further.

[Danack]

setImageDepth() has no effect unless setType() is specified? We'll need a specific use case that we can download and reproduce the problem before we can comment further.

An example from the other issue is below. Yes, it is in PHP as I find that a lot easier to write than C. If absolutely necessary I can convert it to C.

<?php

$imagick = new Imagick();
$imagick->newPseudoImage(200, 200, 'xc:white');
$imagick->setImageFormat('tiff');
$imagick->setImageDepth(16);
$imagick->writeImage("./output_default.tif");
system('identify ./output_default.tif');


$imagick = new Imagick();
$imagick->newPseudoImage(200, 200, 'xc:white');
$imagick->setType(\Imagick::IMGTYPE_TRUECOLOR);
$imagick->setImageFormat('tiff');
$imagick->setImageDepth(16);
$imagick->writeImage("./output_forceTrueColor.tif");
system("identify ./output_forceTrueColor.tif");

[mikayla-grace]

We have a patch in ImageMagick to fix this problem. Its a legacy issue specific to TIFF. setImageDepth() does not resolve the problem, instead use setImageType(), setDepth(), or install the latest GIT source.

[emxjay]

Are you referring to this patch?

[mikayla-grace]

The patch sets the appended images depth to the maximum depth of any one image used to build the result. A different patch removes the TIFF legacy algorithm of automatically reducing a TIFF image to a depth of 1 if the image was determined to be grayscale / monochrome.

[emxjay]

Sweet. Thanks.