Image upscaled for no apparent reason

[bjhijmans]

Brief outline of the bug

I encountered an issue where an image was upscaled by about a third and I don't know why. It seems to be specific to the image, which was resized down using https://imageresizer.com/. I also used another method to scale down the same image and every other application agrees that the two included images are identical in size. But somehow, when I compile them in LaTeX there is a very obvious difference.

Minimal example showing the bug

\RequirePackage{latexbug}
\documentclass[]{article}
\usepackage{graphicx}

\begin{document}
	\begin{figure}
		\centering
		\includegraphics{SameSize(1).png}
		\caption{caption}
	\end{figure}
	
	\begin{figure}
		\centering
		\includegraphics{SameSize(2).png}
		\caption{caption}
	\end{figure}
\end{document}

I included the two images below. As you can see, they're two identical red triangles. Somewhere in LaTeX internals the decision is made that one of them should be about 33% bigger.

Log file (required) and possibly PDF file

test.log
test.pdf

[u-fischer]

well I can no access the real images and without them it is difficult to say something. Probably they have different resolution. You should also check if pdflatex renders them differently too and not only xelatex.

[davidcarlisle]

if you use pdflatex the size is obtained by running extractbb (which is dvipdfmx essentially), it reports

%%Creator: extractbb 20220710
%%BoundingBox: 0 0 79 150
%%HiResBoundingBox: 0.000000 0.000000 79.000000 150.000000
%%CreationDate: Thu Feb 15 10:58:12 2024

for the first and

%%Creator: extractbb 20220710
%%BoundingBox: 0 0 59 113
%%HiResBoundingBox: 0.000000 0.000000 59.258271 112.515705
%%CreationDate: Thu Feb 15 10:58:29 2024

for the second.

So it is not really a latex issue as it is being given different sizes.

The images are the same in pixel size but have different metadata setting resolution

gimp shows the first as

gimp shows the second as

[bjhijmans]

@davidcarlisle that's very interesting. I will admit I don't know much about image metadata. I also accept that I may be entirely in the wrong place with this. I assumed, apparently incorrectly? that the print size would be the number of pixels divided by the DPI. Windows, at least, reports a DPI of 96 for both images and the same size in pixels.

Is the offending image's metadata internally inconsistent?

It still looks to me like LaTeX, apparently through extractbb, is looking at different data than other programs are. Is there a standard for this that someone isn't adhering to?

[muzimuzhi]

Windows, at least, reports a DPI of 96 for both images and the same size in pixels.

imagemagick gives different answers

$ identify -units PixelsPerInch -format '%U %x,%y\n' latex2e-gh1277-1.png
PixelsPerInch 72,72
$ identify -units PixelsPerInch -format '%U %x,%y\n' latex2e-gh1277-2.png
PixelsPerInch 95.989999999999994884,95.989999999999994884

Relevant docs

• -units PixelsPerInch https://imagemagick.org/script/command-line-options.php#units
• -format '...' https://imagemagick.org/script/escape.php

[bjhijmans]

I used a different resizer for the image and sent it to my customer, and it still didn't work. It turns out that Gmail also resizes images (for file size, not pixels) and it causes the exact same issue.

I wish I knew what image tools are being used under the hood so that I could submit a bug report there. Images shouldn't scale differently because they've been emailed at some point.

[u-fischer]

you shouldn't sent important binary images as email attachments (or perhaps even embedded in some html). At least put them inside a zip.

[josephwright]

I agree things shouldn't auto-resize, but that's not a LaTeX issue ;)