Masalah penyajian gambar dalam format next-gen yang datang dari thumbnail Blogger ketika diuji menggunakan Pagespeed Insights dan Lighthouse masih menjadi kasus yang belum terpecahkan karena memang Blogger belum mendukung format gambar WEBP untuk thumbnail.
Sementara untuk gambar postingan sudah bisa baik untuk AMP maupun untuk NON AMP. Anda bisa simak pada postingan tentang cara mengkonversi gambar Blogger menjadi WebP untuk amp-img dan gambar WebP pada postingan Blogger Non AMP.
Namun akhirnya saya mendapatkan solusi untuk thumbnail Blogger agar support WEBP dengan bantuan Statically Imgpx dan Lazysizes.js. Tetapi ini masih hanya untuk Non AMP, untuk AMP saya belum mendapatkan solusinya.
Saya memanfaatkan fitur Statically Imgpx untuk merubah gambar Blogger agar bisa support WEBP dengan menggunakan Lazysizes.js untuk merubah URL gambarnya sekaligus untuk lazyload gambarnya.
Jadi dengan ini, 2 masalah di Pagespeed Insights dan Lighthouse bisa teratasi, yaitu Serve images in next-gen formats dan Defer offscreen images.
Dengan Lazysizes.js saya merubah URL gambar Blogger menjadi seperti berikut dengan sedikit memodifikasi script-nya.
URL asli:
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjU4Zy9izEZOhZup9fNGqI-ngomoAl_teEmKf9U_-ZB5Cfd3lkoLJt8ovllo62Qtwn8dOBTAD3rZlvko9DEqCN9uD-ODXxwrRQ0tsCGV11gjmNNkvkaloCnV_iUIdu-opTMm9TaFg0YCv4/w600-h337-p-k-no-nu/Km6K4E05HjM.jpg
https://cdn.statically.io/img/3.bp.blogspot.com/-WvjDGI4wI1Q/XSmKyEfpsuI/AAAAAAAADqc/GGdZ0RndJGc8xBTn3myp0THfQltQKK2vQCLcBGAs/w600-h337-p-k-no-nu/Km6K4E05HjM.jpg?format=webpDan berikut hasil test pada Pagespeed Insights, untuk masalah format dan defer gambar sudah bisa diatasi.
Jika Anda ingin mencobanya, silahkan gunakan kode-kode berikut.
Silahkan simpan script Lazysizes.js yang sudah saya modif untuk merubah URL gambar Blogger menjadi Statically Imgpx.
/*! lazysizes - v5.1.0 */
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<b:if cond='data:post.thumbnailUrl'>
<picture>
<source expr:data-srcset='resizeImage(data:post.thumbnailUrl, 600, "16:9") + "?format=webp"' type='image/webp'/>
<source expr:data-srcset='resizeImage(data:post.thumbnailUrl, 600, "16:9")' type='image/jpg'/>
<img class='lazyload' expr:alt='data:post.title' expr:data-src='resizeImage(data:post.thumbnailUrl, 600, "16:9")' expr:title='data:post.title' height='9' src='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAJAQMAAAAB5D5xAAAAA1BMVEUAAACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjwA0AABsAAQrj5HwAAAAASUVORK5CYII=' width='16'/>
</picture>
</b:if>
<b:if cond='data:post.thumbnail'>
<div class='item-thumbnail'>
<picture>
<source expr:data-srcset='resizeImage(data:post.thumbnail, 138, "16:9") + "?format=webp"' type='image/webp'/>
<source expr:data-srcset='resizeImage(data:post.thumbnail, 138, "16:9")' type='image/jpg'/>
<img class='lazyload' expr:alt='data:post.title' expr:data-src='resizeImage(data:post.thumbnail, 138, "16:9")' expr:title='data:post.title' height='9' src='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAJAQMAAAAB5D5xAAAAA1BMVEUAAACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjwA0AABsAAQrj5HwAAAAASUVORK5CYII=' width='16'/>
</picture>
</div>
</b:if>Mungkin ada yang bertanya, kenapa menggunakan tag
<picture>? Karena sampai saat ini belum semua browser support format gambar WEBP. Dengan tag <picture> maka di situ kita juga menyediakan fallback gambar *.jpg untuk browser-browser yang belum support WEBP.Yang saya harapkan dari Blogger, bisa modif kode thumbnail blogger seperti untuk resizeImage sehingga kita bisa modif url untuk param image blogger.
Semoga bermanfaat.
Adhy Suryadi