Dark thumbnails?

[Brandon Weigel]

Hello all..

I've experienced a strange phenomenon in one of my Large Image collections, where certain images' thumbnails are extremely dark, so as to be nigh unusable.

Collection: http://doh.arcabc.ca/islandora/object/sicamous:photographs

Example object: http://doh.arcabc.ca/islandora/object/sicamous:60

If you look at the images themselves (both JP2 derivative and the original TIFF), the contrast is fine; only the Thumbnail is darkened.

The contributors of these images alerted me to the problem, and noted that when she downloaded the TIFF and resized it to make her own thumbnail, it looked a lot better than the Islandora-generated one.

Any ideas what's causing this, and how it might be remedied?

[Brandon Weigel]

A little bit of research brings this up: https://www.bennadel.com/blog/2825-fixing-grayscale-png-thumbnail-images-that-come-out-too-dark-in-imagemagick-6-7-7.htm

Is ImageMagick doing as this blogger surmises, and generating a PNG-8 that can't express all the tones appropriately?

Has anyone else run into this, and perhaps fixed it? What version of ImageMagick are we running?

[Daniel Lamb]

Brandon,

We've had issues before with imagemagick spitting out black thumbnails for pdfs, and the solution was to tweak the command: https://groups.google.com/forum/#!topic/islandora/ztY0Iv5-0AU.  So it's certainly within the realm of possibility.

To find out what version you are using, issue "convert --version" from a command prompt.  From the sounds of the blog post, newer versions fix it.  So it may be as simple as updating imagemagick.  To my knowledge, the newest imagemagick _should_ be ok.  I know people run the latest package from Ubuntu 16.04 without issue, which should be newer than that blog post at least.

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~Danny Lamb
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[Peter MacDonald]

Brandon:

I noticed that in your example object

Example object: http://doh.arcabc.ca/islandora/object/sicamous:60

​the preview (navigation) window in the top right corner of the image is also black -- even though the navigation in it works.

We have the same problem with some of our large black and white images, e.g.

• http://asa.dhinitiative.org/islandora/object/HamiltonShahid:94
  

but not all of our black and white images -- even within the same collection, e.g.

• http://asa.dhinitiative.org/islandora/object/HamiltonShahid:97

With color images, I've never seen this problem.

I'm just saying (confirming?) that your problem may have something to do with how imagemagick handles just black and white images.

I'm sorry I don't have a solution yet.

Peter​

Peter MacDonald
Library Information Systems Specialist
Hamilton College Library
315 859-4493
Skype: pmacdona-hamilton

On Mon, Feb 5, 2018 at 10:21 AM, Daniel Lamb <dl...@islandora.ca> wrote:

Brandon,

We've had issues before with imagemagick spitting out black thumbnails for pdfs, and the solution was to tweak the command: https://groups.google.com/forum/#!topic/islandora/ztY0Iv5-0AU.  So it's certainly within the realm of possibility.

To find out what version you are using, issue "convert --version" from a command prompt.  From the sounds of the blog post, newer versions fix it.  So it may be as simple as updating imagemagick.  To my knowledge, the newest imagemagick _should_ be ok.  I know people run the latest package from Ubuntu 16.04 without issue, which should be newer than that blog post at least.

On 2018-02-05 10:54 AM, Brandon Weigel wrote:

A little bit of research brings this up: https://www.bennadel.com/blog/2825-fixing-grayscale-png-thumbnail-images-that-come-out-too-dark-in-imagemagick-6-7-7.htm

Is ImageMagick doing as this blogger surmises, and generating a PNG-8 that can't express all the tones appropriately?

Has anyone else run into this, and perhaps fixed it? What version of ImageMagick are we running?

On Monday, 5 February 2018 09:50:07 UTC-5, Brandon Weigel wrote:

Hello all..

I've experienced a strange phenomenon in one of my Large Image collections, where certain images' thumbnails are extremely dark, so as to be nigh unusable.

Collection: http://doh.arcabc.ca/islandora/object/sicamous:photographs

Example object: http://doh.arcabc.ca/islandora/object/sicamous:60

If you look at the images themselves (both JP2 derivative and the original TIFF), the contrast is fine; only the Thumbnail is darkened.

The contributors of these images alerted me to the problem, and noted that when she downloaded the TIFF and resized it to make her own thumbnail, it looked a lot better than the Islandora-generated one.

Any ideas what's causing this, and how it might be remedied?

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~Danny Lamb
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Islandora Foundation
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[dric...@utk.edu]

Is the original image CMYK or RBG? Maybe adding "-colorspace RGB -set colorspace sRGB -colorspace CMYK -set colorspace CMYK " to imagemagick will help avoid this mismatch in the future. 

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~Danny Lamb
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[Brandon Weigel]

Adding those bits created a straight black thumbnail, so that didn't work. :)  

Opening the TIFFs in Photoshop, as far as I can tell, they're RGB 8-bit... File info says photoshop:colormode:3.

Not having much luck so far!

[dp...@metro.org]

Hi Brandon,

Did a convert to your TIFF source image and I got some pretty decent TN after removing the -colorspace RGB recently merged. See

Same with -colorspace RGB 

Since "identify" applied on the image shows that TN is already in RGB space, maybe we could avoid using colorspace at all if we can identify those that are CMNYK and need this (i named your file brandon.tiff)

. identify brandon.tiff  

brandon.tiff TIFF 3928x6378 3928x6378+0+0 8-bit sRGB 23.9504MiB 0.000u 0:00.009

This is my imagemagick

identify --version

Version: ImageMagick 7.0.7-3 Q16 x86_64 2017-09-22 http://www.imagemagick.org

Copyright: © 1999-2017 ImageMagick Studio LLC

License: http://www.imagemagick.org/script/license.php

Features: Cipher DPC HDRI Modules 

Delegates (built-in): bzlib freetype jng jp2 jpeg lcms ltdl lzma png tiff xml zlib

Best

Diego Pino

metro.org

[Daniel Lamb]

Diego++

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[dp...@metro.org]

Hi, me again

Changing -colorspace RGB to -colorspace sRGB leads to better results (see below). Committers, any objections on doing that change globally?

best

Diego

[Brandon Weigel]

Assuming sRGB doesn't hurt the thumbnails generated for other types of images, I'd be happy to see it changed globally.

[dp...@metro.org]

Brandon, can you ping Jon Green and ask him? If sRGB does not hurt his needs, I can make this pull tonight.

Cheers

[Brandon Weigel]

Not sure how to ping him; he doesn't show up in Jira tagging. 

[dp...@metro.org]

Ok, trying on IRC now and discussing, seems like there is green light, jon++. http://irclogs.islandora.ca/2018-02-05.html

[dp...@metro.org]

Brandon, could you make me the honors to open a JIRA ticket and tag me there?

Thanks

[Brandon Weigel]

Done! Thank ye kindly.

[dp...@metro.org]

Cool. Working on a full fix here that involves an identify call, so stay tuned. Thanks for opening the JIRA ticket

D