TYPO3 Gridelements render FAL Image using Fluidtemplate

I'm using TYPO3 8.7 and the latest extension gridelements (8.2.3). Now I want to show/render an image in my FLUIDTEMPLATE.. - but I don't know how?!?

Here's my TypoScript:

tt_content {
    gridelements_pi1 = COA
    gridelements_pi1 {
        20 {
            10 {
                setup {
                    SectionColoured < lib.gridelements.defaultGridSetup
                    SectionColoured {
                        cObject = FLUIDTEMPLATE
                        cObject {
                            file = EXT:myext/.../SectionColoured.html
                        }
                    }
                }
            }
        }
    }
}

Now, I upload an image (e.g. for background-image) via flexforms, like this:

<backgroundimage type="array">
                        <TCEforms type="array">
                            <label>LLL:EXT:autefa/Resources/Private/Language/backend.xlf:gridelements.SectionColoured.flexforms.backgroundimage</label>
                            <config type="array">
                                <type>inline</type>
                                <maxitems>1</maxitems>
                                <foreign_table>sys_file_reference</foreign_table>
                                <!--<foreign_field>uid_foreign</foreign_field>-->
                                <foreign_table_field>tablenames</foreign_table_field>
                                <foreign_label>uid_local</foreign_label>
                                <foreign_sortby>sorting_foreign</foreign_sortby>
                                <foreign_selector>uid_local</foreign_selector>
                                <foreign_selector_fieldTcaOverride type="array">
                                    <config>
                                        <appearance>
                                            <elementBrowserType>file</elementBrowserType>
                                            <elementBrowserAllowed>jpg,png</elementBrowserAllowed>
                                        </appearance>
                                    </config>
                                </foreign_selector_fieldTcaOverride>
                                <foreign_match_fields type="array">
                                    <fieldname>image</fieldname>
                                </foreign_match_fields>
                                <appearance type="array">
                                    <newRecordLinkAddTitle>1</newRecordLinkAddTitle>
                                    <headerThumbnail>
                                        <field>uid_local</field>
                                        <height>64</height>
                                        <width>64</width>
                                    </headerThumbnail>
                                </appearance>
                            </config>
                        </TCEforms>
                    </backgroundimage>

That works so far. How can I use the image in my FLUIDTEMPLATE? The debugger returns 12 on {data.flexform_backgroundimage} ?!

<f:debug>{data.flexform_backgroundimage}</f:debug>
<section class="main-content {data.flexform_farbe}">
    <article>
        <f:format.raw>{data.tx_gridelements_view_columns.101}</f:format.raw>
    </article>
</section>

Debug {data}.. THanks for your help!

pi_flexform => array(1 item)
      data => array(1 item)
         general => array(1 item)
            lDEF => array(2 items)
               farbe => array(1 item)
               backgroundimage => array(1 item)
                  vDEF => '12' (2 chars)

Edit: image

It's funny. If I try it with the TYPO3 Fluid ViewHelper:

<section style="background-image:url({f:uri.image(src: '{data.flexform_backgroundimage}', treatIdAsReference: 1)})">
    <article>
        <f:format.raw>{data.tx_gridelements_view_columns.100}</f:format.raw>
    </article>
</section>

I'll get an error You must either specify a string src or a File object.

Now I use vhs:

{namespace v=FluidTYPO3\Vhs\ViewHelpers}

<section style="background-image:url({v:uri.image(src: '{data.flexform_backgroundimage}', treatIdAsReference: 1)})">
    <article>
        <f:format.raw>{data.tx_gridelements_view_columns.100}</f:format.raw>
    </article>
</section>

And everything works .. here's the view helper reference of the vhs extension. Thanks for the helping guys!