Colors changing under graphic inclusion with graphicx

Question

I have (a couple) of PNG images with a background color of, for example, RGB(80,64,83):

that when placed on a page of the same background color with graphicx -- they show a distinct tonality against the background -- which is of the same color, when run under XeLaTeX. There are no problems under pdfLaTeX or LuaLaTeX.

\documentclass{report}

\usepackage{xcolor}
\definecolor{bgcolor}{RGB}{80,64,83}

\usepackage{graphicx}
\pagestyle{empty}

\begin{document}

\pagecolor{bgcolor}
\includegraphics[width=0.5\textwidth]{A.png}
\quad
\includegraphics[width=0.5\textwidth]{B.png}

\medskip

\includegraphics[width=0.5\textwidth]{A-gimp.png}
\quad
\includegraphics[width=0.5\textwidth]{B-gimp.png}

\end{document}

Checking the colors in the included files one can see they have changed from (80,64,83) to (71,56,74) in the included images.

Just opening the images on GIMP and exporting it as-is with the default choices of

fixes everything and the new inclusion now gets the exact color they were set to begin with, the same as the background, as shown below (second line). Also processing the images with pdflatex or lualatex does not show the problem.

What is that XeTeX needs from the PNG's to preserve their color when included in a page?

For experimentation here are the same images, after opening and closing with GIMP:

Edit on Jan 10, 2021: The problem only displays when run under XeLaTeX. There are no problems under pdfLaTeX or LuaLaTeX.

Edit on Jan 11, 20201: Ulrike Fischera (at TeXhax) have determined the problem lies with dvipdfmx, the backend of xetex processing. She and and David Purton (below) looking at the PDF found that it uses the wrong color space (CalRGB) for the first two images and DeviceRGB for the last two.

Answer 1

There are some colour space related differences between your original images and the ones saved through Gimp.

You can see them using identify -verbose from ImageMagick.

Inspecting the resulting PDF file shows that your original PNGs end up using the CalRGB colour space, while the Gimp ones just use DeviceRGB. This is enough to create the colour shift in your PDF.

I think your best option is to remove all the ICC colour profile information from your original PNG files. This will ensure that the images in the PDFs are treated in the same way as your solid colours.

Again, you can do this using ImageMagick:

Just run: mogrify -strip A.png.

Answer 2

Three PNG images created with GIMP with RGB values of 71,56,74; 79,62,82 and 80,64,83, respectively:

1.png:       2.png:       3.png:

Now framed: The first row have frames in a distinctive color for reference. The second row have the same frmaes but frames with color defined in LaTeX that should match the image color. The other two rows have the same frames with in different position for close comparison of the three colors.

\documentclass{article}
\usepackage{graphicx}
\usepackage{xcolor}
\definecolor{color1}{RGB}{71,56,74}
\definecolor{color2}{RGB}{79,62,82}
\definecolor{color3}{RGB}{80,64,83}
\begin{document}
%\pagecolor{color3}
\fboxsep15pt
\fcolorbox{red}{olive}{\includegraphics{1.png}}
\fcolorbox{red}{olive}{\includegraphics{2.png}}
\fcolorbox{red}{olive}{\includegraphics{3.png}}\par
\fcolorbox{red}{color1}{\includegraphics{1.png}}
\fcolorbox{red}{color2}{\includegraphics{2.png}}
\fcolorbox{red}{color3}{\includegraphics{3.png}}
\fcolorbox{red}{color2}{\includegraphics{1.png}}\par
\fcolorbox{red}{color3}{\includegraphics{2.png}}
\fcolorbox{red}{color1}{\includegraphics{3.png}}
\fcolorbox{red}{color3}{\includegraphics{1.png}}\par
\fcolorbox{red}{color1}{\includegraphics{2.png}}
\fcolorbox{red}{color2}{\includegraphics{3.png}}
\end{document}

As you can see here, LaTeX defined colors match perfectly by the RGB values of the images.

Note that your first original PNG is not the "color3" in my example, but "color2" (at least in Chrome, Xviewer or color-picker, the RGB value is 79,62,82).

For some reason, in your first file (but not in my file 2.png) that have 79,62,82 ("color2") is showe in LaTeX PDF as 71,56,74 ("color1") whereas in Gimp window changed to 80,64,83 ("color3"). I have no idea if this happens because your file is indexed, corrupt or something else. With three different interpretations of the same file is hard to say which program is wrong or why. But when the PNG is made or saved by Gimp (2.png) there are not different interpretations of what it should be in the PDF of LaTEX, the imaged posted here, or in the Gimp window, so it seems not a problem of LaTeX, but of the original image. Maybe a non-standard PNG file header?