Welche Fluid Version? Bzw. Welche Typo3 Version?
So zum Beispiel Typo3 7:
<picture>
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '1920')}" media="(min-width: 1601px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '1600')}" media="(min-width: 1334px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '1333')}" media="(min-width: 1001px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '1000')}" media="(min-width: 801px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '800')}" media="(min-width: 601px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '600')}" media="(min-width: 401px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '400')}" media="(min-width: 321px)">
<source srcset="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '320')}" media="(min-width: 200px)">
<img src="{f:uri.image(src:'{column.media.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{data.imageheight}', maxHeight: '{data.imageheight}', width: '{data.imagewidth}', maxWidth: '{data.imagewidth}')}"
{f:if(condition: '{data.imagewidth}', then: 'width="{data.imagewidth}"')}
{f:if(condition: '{data.imageheight}', then: 'height="{data.imageheight}"')}
title="{column.media.title}"
alt="{column.media.alternative}">
</picture>
und hier für Typo3 8 (musst du die werte halt anpassen):
<picture>
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '1920')}" media="(min-width: 1601px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '1600')}" media="(min-width: 1334px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '1333')}" media="(min-width: 1001px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '1000')}" media="(min-width: 801px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '800')}" media="(min-width: 601px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '600')}" media="(min-width: 401px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '400')}" media="(min-width: 321px)">
<source srcset="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'smartphone', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '320')}" media="(min-width: 200px)">
<img src="{f:uri.image(src:'{file.uid}', treatIdAsReference:'1', cropVariant: 'default', height: '{h}', maxHeight: '{data.imageheight}', width: '{w}', maxWidth: '{data.imagewidth}')}"
{f:if(condition: '{data.imagewidth}', then: 'width="{data.imagewidth}"', else: 'width="{w}"')}
{f:if(condition: '{data.imageheight}', then: 'height="{data.imageheight}"', else: 'height="{h}"')}
/>
</picture>