![\"davide_barranca\"](\"https:\/\/www.knowhowtransfer.com\/store\/wp-content\/uploads\/2014\/05\/davide_barranca.jpg\")
<\/a>By Davide Barranca<\/p>\nEquirectangular images, the ones used to build those beautiful, immersive, 360 degrees panoramas<\/a>, may require some extra attention with ALCE<\/a> , in order to avoid processing differences near the image’s borders: which must blend seamlessly in the final file.<\/p>\n The italian photographer Alfonso Grotta<\/a> has kindly given me the permission to use this wonderful image (part of a virtual tour he did over the past 3 years to document the Somma<\/em> chapel restoration, in the San Giovanni a Carbonara<\/em> church in Naples, Italy) to show a suggested workflow.<\/p>\n An equirectangular<\/a> image is a stitch of several single shots, that covers 360\u00b0 horizontally (a full circle), and 180\u00b0 vertically (top to bottom). In the resulting panorama (a quicktime\/flash\/html movie) the image is wrapped around a sphere, so that the top and bottom lines of the borders are condensed into a single point (zenit and nadir) and the left and right borders touch themselves in a meridian. A true equirectangular file must have the exact 1:2 ratio<\/strong>(e.g. 1000 x 2000 px), not a pixel more, not a pixel less. To be successful with ALCE in your 360\u00b0 panoramas, you should follow just a couple of simple suggestions.<\/p>\n It builds the local mask (used by the routine to boost the contrast) in a way that doesn’t fit well with the image’s subsequent processing (i.e. the VR movie).<\/p>\n If you keep having troubles with the left\/right borders after ALCE, please try the following: (I suppose you have a flat, single layer, equirectangular image in Photoshop and you know its width in pixels – check it from the Image – Image Size..<\/em>. menu).<\/p>\n Photoshop filter Offset, first iteration with positive value<\/p><\/div>\n For instance if your image is 3500px wide, offset it by 3500\/2 = 1750 pixels. Don’t worry if the width is odd (for instance 3543 pixels): pick up either 3543\/2 = (1770 or 1771), it’s not a problem at all, but write down the value somewhere. You’ll see that the whole image is… offset on the right (compare it with the one at the post start).<\/p>\n Result of the Offset filter (180 shift in the Yaw)<\/p><\/div>\n We’re almost done, but to recap: we’ve offset to the right a copy of a layer, processed it with ALCE and offset it back to left. Then we’ve applied ALCE to the original layer. The unprocessed layers have gone to the trash.<\/p>\n <\/p>\n The Layer mask for the BORDERS layer<\/p><\/div>\n Actually, painting a couple of large, soft brush strokes with white in the layer mask would have been enough, nevertheless the mirrored gradient is… much more elegant, don’t you agree?<\/p>\n That’s it, I hope you’ve found this little trick useful – it can be used not only for ALCE, but also with all kind of elaborations that may give edge troubles with equirectangular images.<\/p>\n I wish to thank again the photographer Alfonso Grotta<\/a> for the kind permission to use his picture. If you’re interested in the San Giovanni a Carbonara church virtual reality tour he made (and high resolution stills to document the restoration), it’s included in the companion CD of a dedicated book<\/a>.<\/em><\/p>\n Lives and works near Bologna, Italy. Two suggestion for ALCE processing of equirectangular images to be used building 360 degree panoramas.<\/p>\n","protected":false},"author":10,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[7,111],"tags":[],"class_list":["post-5944","post","type-post","status-publish","format-standard","hentry","category-alce","category-photography"],"_links":{"self":[{"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/posts\/5944","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/users\/10"}],"replies":[{"embeddable":true,"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/comments?post=5944"}],"version-history":[{"count":0,"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/posts\/5944\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/media?parent=5944"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/categories?post=5944"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.knowhowtransfer.com\/store\/wp-json\/wp\/v2\/tags?post=5944"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Avoid the Turbo<\/h3>\n
First, you should not select the Turbo processing: while it’s perfectly fine (and a lot faster) for normal, single images, it’s not recommended with equirectangular files.<\/p>\nOffset<\/h3>\n
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icon in the layer palette, or select the layer and Layer – Layer Mask – Reveal All<\/em>).<\/li>\n<\/li>\n<\/ol>\n\n
Now your Layers palette should look like the image at the left: if it doesn’t, please review the steps above. You can now flatten the file and save it.<\/p>\n
\nDavide Barranca<\/h3>\n
He’s the developer of ALCE, VitaminBW, Double USM, PS Projects and Floating Adjustments.
Davide is also a color-management aware photo-retoucher, focused in color-correction and image enhancement in fine-art photography, art reproduction photography and fine-art digital printing. Interested in academic research around digital imaging, stitching, HDRI, custom filters writing.
Specialties: Pre-press, broad experience in working side by side with photographers trying to convert from artist to technical language.
You can visit his site here ><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"