How to set alternative texts in Typst output using ggplot?

[JosephBARBIERDARNAL]

Description

Hi!

I'm trying to set the alternative text in images from ggplot output using Typst format. The issue is, I couldn't find a way to add alt text. For instance, none of the following work:

---
title: "hello"
format:
   typst:
      keep-typ: true
---

```{r}
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "example alt text")
```

```{r}
#| fig-alt: "yet another alt text"
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "still alt!")
```

(relevant) typst output is:

```r
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "example alt text")
```

#box(image("reprex_files/figure-typst/unnamed-chunk-1-1.svg"))

```r
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "still alt!")
```

#box(image("reprex_files/figure-typst/unnamed-chunk-2-1.svg"))

I wish it would be:

```r
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "example alt text")
```

#box(image("reprex_files/figure-typst/unnamed-chunk-1-1.svg", alt: "example alt text"))

```r
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "still alt!")
```

#box(image("reprex_files/figure-typst/unnamed-chunk-2-1.svg", alt: "still alt!")) // or the other alt text, not sure which one it should be

In ggplot we're supposed to use labs(alt="hello"), but this might be different when using Quarto. But it seems that fig-alt does not work either.

Maybe I misunderstood this section in the doc (or maybe it's just for for Jupyter?).

[JosephBARBIERDARNAL]

I think I have my answer, according to https://quarto.org/docs/reference/formats/typst.html#figures , fig-alt is not implemented yet?

[mcanouil]

That's possible as the version of Typst being shipped in Quarto is not the latest and update needs to be done carefully to ensure Pandoc/Quarto/Typst keep playing as expected together.

Also, most of the fig- options implies there is a "figure" not to be confused with an "image".
A figure has a caption and can be referenced while an image cannot.

[mcanouil]

In addition, Pandoc's writer for typst does not seem to support alt-text which might be the main reason for Typst in Quarto not supporting this option.

echo '![Caption "some title"](image.png){alt="Alt text describing the image"}' | quarto pandoc -f markdown -t typst
echo '![Caption "some title"](image.png){alt="Alt text describing the image"}' | pandoc -f markdown -t typst

More generally Pandoc's writer does seem to allow only the height/width attributes.

• https://github.com/jgm/pandoc/blob/09c9be2c12c50bc4a6a590fb43b92eb67758af94/src/Text/Pandoc/Writers/Typst.hs#L540-L559

[cderv]

My understanding is that Alt text support is coming in Typst in next 0.14 version through Accessibility in PDF update: https://staging.typst.app/docs/changelog/0.14.0

Work was done in

• Generate tagged PDF documents for accessibility typst/typst#6619

This is not yet available in Quarto, and also Pandoc needs to adapt for sure.

[mcanouil]

There are two levels for alternative text: image (already in current Typst version) and figure (0.14).

#figure(
  image("quarto.png", alt: "some alt"),
  alt: "figure level alt text",
  caption: [
    Caption
  ]
)

Pandoc supports no attributes but height/width and the caption.

echo '![](image.png){alt="Alt text describing the image"}' | pandoc -f markdown -t typst 

#box(image("image.png"))

[cderv]

Thanks - that is helpful distinction! We should look into what Quarto already supports. We may completely rely on Pandoc for images and Quarto figures. I assumed Figure support because this is what I think we use for crossreference figures and Pandoc Figure AST node (and not Image node)

[mcanouil]

Caption/cross-ref means "figure".
So in those cases "alt" at figure level should be used.
But images should still be supported in my opinion but these should likely comes from Pandoc's writer.

echo '![](image.png){alt="Alt text describing the image"}' | pandoc -f markdown -t native

Pandoc AST

[ Para
    [ Image
        ( ""
        , []
        , [ ( "alt" , "Alt text describing the image" ) ]
        )
        []
        ( "image.png" , "" )
    ]
]

echo '![This is a figure](image.png){alt="Alt text describing the image in the figure"}' | pandoc -f markdown -t native

Pandoc AST

[ Figure
    ( "" , [] , [] )
    (Caption
       Nothing
       [ Plain
           [ Str "This"
           , Space
           , Str "is"
           , Space
           , Str "a"
           , Space
           , Str "figure"
           ]
       ])
    [ Plain
        [ Image
            ( "" , [] , [] )
            [ Str "Alt"
            , Space
            , Str "text"
            , Space
            , Str "describing"
            , Space
            , Str "the"
            , Space
            , Str "image"
            , Space
            , Str "in"
            , Space
            , Str "the"
            , Space
            , Str "figure"
            ]
            ( "image.png" , "" )
        ]
    ]
]

[JosephBARBIERDARNAL]

My understanding is that Alt text support is coming in Typst in next 0.14 version through Accessibility in PDF update: https://staging.typst.app/docs/changelog/0.14.0

Work was done in

* [Generate tagged PDF documents for accessibility typst/typst#6619](https://github.com/typst/typst/pull/6619)

This is not yet available in Quarto, and also Pandoc needs to adapt for sure.

I should have specified that I am using typst 0.14 (with the QUARTO_TYPST environment variable) and that even though it makes a big difference in terms of accessibility, it does not add alternative text here. As you said later, this is probably related to knitr/ggplot instead.

[mcanouil]

Let me clarify, there are two issues which are actually not related here and now:

• labs(alt = ...) is not being forwarded. If you use format: html which fully support setting alternative text, you can see the issue about knitr/ggplot. It's unrelated to Typst.
• Pandoc (thus Quarto) does not support the alt argument of image (Typst 0.13) and alt argument at figure level (Typst 0.14). So, unless you write Typst code yourself, there is no way to have alternative-text using the figure markdown syntax (this figure/image produced inside code cells). (More generatlly Pandoc does not support any of the other arguments of image/figure except for width and height How to set alternative texts in Typst output using ggplot? #13596 (reply in thread))

[cderv]

Reading again the issue, I know see this is a ggplot and knitr issue in a way.

This is the intermediate markdown output for the first cell

::: {.cell}

```{.r .cell-code}
library(ggplot2)

ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "example alt text")
```

::: {.cell-output-display}
![](index_files/figure-typst/unnamed-chunk-1-1.svg)
:::
:::

You can see that labs(alt=) does not go through knitr processing. They added the alt text feature in

• Add alt-text functionality tidyverse/ggplot2#4482

with a not to propagate to knitr, but I don't think this is yet done.

So the issue won't probably be with typst but all format.

Though they did provide a retreiver function ggplot2::get_alt_text() and using knitr options feature, it can be used this way.

```{r}
#| fig-alt: !expr last_alt
library(ggplot2)

p <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "example alt text")
last_alt <- ggplot2::get_alt_text(p)
p
```

Leading to

::: {.cell}

```{.r .cell-code}
library(ggplot2)

p <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(alt = "example alt text")
last_alt <- ggplot2::get_alt_text(p)
p
```

::: {.cell-output-display}
![](index_files/figure-typst/unnamed-chunk-1-1.svg){fig-alt='example alt text'}
:::
:::

This is because that options like fig-alt are evaluated by knitr only after the cell is evaluated.

So what is really missing is for ggplot2 to have a way to pass the alt text to knitr, or to knitr directly to retrieve (which is probably what yihui/knitr#2001 is about and we need to revisit)

[cderv]

Though it does not solve the issue for fig-alt correct support for Typst output.