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I have read articles all over the internet today. While some questions and answers are similar to my issue, none precisely cover my problem.

I am currently doing CAD work for a website where my images will need to go on multiple colour backgrounds. Ordinarily in the jewellery trade rings are rendered on white which is very simple to blend in with websites.

In essence, I need to be able to preserve a ring and the shadow it casts on a transparent background. This means that the shadow, currently rendered on white, must look good on any colour. Without the shadow the ring looks very out of place on the page.

So I have explored my options, and using Multiply I have managed to create:

  1. a bottom layer of whichever colour the web page is
  2. a middle layer of the ring rendered on white with the shadows (Multiply)
  3. a top layer of ring highlights for the colour background I want.

Here is the final result:

enter image description here

The issue with this method is that it makes the image look seamless when pasted on a webpage for Windows users, but Mac users see the block colour difference clear as day.

Example 1: What mac users see in example 2

Example 2: Windows users will generally see this as seamless, Mac users will still see a difference in colour:

Here is the render on a white background, and here is the alpha, and here is the cutout of the ring with reflection colours correct for #eb472c:

  1. enter image description here
  2. enter image description here
  3. enter image description here

So I want to be able to have the ring and its shadow on a transparent background. This will negate the need to mess around with colour matching with web pages. The best way to describe it would be to have the Multiply effect, but rather than choosing the bottom layer as a colour to blend with, to have it blend with transparent.

Colour range selection does not work for this problem as the shadow needs to blend over many different colour backgrounds.

Many thanks for any help.

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If you can render the object on both a black and a white background, you can apply the answer I gave to this question to reconstruct the transparency. Note that, depending on how you do the background color change, this may result in the reflections also becoming semitransparent (which may actually be desirable). –  Ilmari Karonen Oct 27 '13 at 0:26
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1 Answer 1

up vote 3 down vote accepted

Because you are using CAD software, you ought to be able to work out how to make a mask of the object. I am perplexed about why can't export this from your CAD software without a color background, but will assume you can't.

If you texture or light the ring in such a way that it is pure black without lighting, but with a white background, you can then export a greyscale of the silhouette of the object, then you can export a greyscale of the item with shadow, and then a full-color version ("normal").

switch to photoshop.

edit: rewrite with pics

  • use the mask you provided as "ring mask"

  • dupe the ring mask layer, dupe the greyscale image

  • invert the ring mask copy so it is black ring on white

  • merge with greyscale copy and then invert. This is "shadow mask"

  • make the foreground color swatch the exact red you used in background

  • make the ring with red on a white background the active layer active (your color image 3 above)

  • select -> color range, sample the foreground red swatch, adjust to suit, but keep it above maybe "100" (promiscuous color select)

  • make a new layer, keep the selection active, and fill with black. this is "reflect mask"

  • apply the ring mask to the greyscale ring layer (layer mask), then set the layer mask active, ctrl+click on "reflect mask", delete selection derived from reflect mask from the current layer mask

    • make a new layer under the greyscale ring, fill with black, apply the shadow mask as a layer mask, then create a selection using the "reflect mask" again and delete that selection from the shadow mask as in the previous step.
  • profit. see images

ring, shadow, reflect masks:

ring mask shadow mask color mask

greyscale with masks; black layer with masks:

greyscale with ring mask less color mask black layer with ring mask less color mask

final with blue

layers palette

{edit}

The steps above are "how" it is done, the following is "why":

We start with the ring images as layers (the images labeled 1, 2,and 3 in the question). We create two additional layers derived from components of these layers and hide them (named "shadow mask" and "reflect mask"). We use these additional layers as a way to store the selection for easy recall later. When we want to load that selection, we can ctrl+click the layer and a selection will be created.

We create a layer mask on the ring image to knock out the background by recalling the proper stored selection layer ("ring mask"), then use the "reflect mask" stored selection to knock out the inner portions of this new layer mask.

Similarly, we do this with a plain black layer and recall the "shadow mask" selection to create the shadows, and then recall the "reflect mask" selection to knock out the inside of the mask.

The blue layer in my example is for visual checks and is hidden for the final export.

Note that the only layer with an image from the original question that is set to "visible" in the final is image #1.

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dont get it, make a quick video. –  Muhammad Umer Jan 10 '13 at 23:14
1  
This answer has really helped me. I would like to elaborate on some of the points you have given here. What is most important, for example, is finishing with a transparent BG. Your method allows this to happen though in your example you have chosen blue. Secondly I should let you know that I'm using Vray for Rhino. There are confirmed bugs in outputting just the shadows hence this big work around. I will create a new answer, modifying your advice here with a guide how I created the effect needed. So thank you very much for your assistance, you have put in a tremendous amount of time and effort –  Peter Jan 11 '13 at 12:29
    
You are welcome and thank you for the comments. I of course only used the blue for illustrative purposes, when exporting, you hide the blue background and the result is a alpha transparency wherever you see the blue. –  horatio Jan 11 '13 at 15:50
    
I'm trying to follow along with this but I can't seem to get it -- I find the instructions rather hard to follow. –  Johannes Sep 23 '13 at 20:56
    
in the description, I use the term "color mask", but in the image of the layers, it is labeled as "reflect mask". If you can identify which steps are confusing, I may be able to clarify –  horatio Sep 24 '13 at 15:57
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