Strange behaviour when using blending modes with some options

Question

Approximately the same question was raised in some forums in particular and on this. But I extended the question to the point that it was necessary to give him a concrete answer.

Look at the picture, each layer has the same blending mode. Each layer is created in different ways. The first 2 layers are not ordinary (you can not draw on them). But you can notice that when they are superimposed on the underlying picture, the effect is the same.

We go further 3rd layer the most ordinary and if someone did any special effects with flashes, he would not use the 2 previous methods. However, you can see that the effect of applying a normal layer to the underlying image is different, although the blending mode in these three cases is the same. Go ahead. Let's take a look at the last 2 layers.

The 4th layer is the same as the previous layer, but the transparency shape layers checkbox is off, but due to its shutdown, the usual layer was superimposed on the underlying image as the 2 first layers. And the last layer, too, is normal. In it, the tick transparency shape layers is enabled. But the picture is drawn with the help of the layer property - gradient fill with blending mode as well as all previous layers.

I told you how each layer was created, and now I want to ask a question. Of all the layers, the 3rd layer correctly affects the bottom layer (in terms of the color dodge mode algorithm). The other layers do not affect the color dodge algorithm.

I suspect that the formula for the color dodge algorithm changes and it involves another variable called opacity. But unfortunately, I could not find not the formula not explaining why the blending effect becomes different.

If the question is not too clear, here is its brief excerpt: Why the 3rd layer does not work like the rest with the same blending mode

P.S I left my PSD file here for deep understanding my question if my words not enough for it.

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Update another picture for illustrate problem

PSD here

Answer 1

Adobe has implemented the blending modes in Photoshop so inconsistently that they have hidden all exact numeric data about it, only some sparse qualitative information is available in tutorials and manuals

The only easy to find quantitative information of Adobe's blending modes talks only about PDFs. It's here:

https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/pdf_reference_archives/blend_modes.pdf

Of course, it's useless when one wants to know how Photoshop's layer blending options affect the calculations of the blending modes.

I have found that layer blending option "Transparency Shapes Layer" affects if the layer is bitmap data layer and the blending mode is one of the following:

• color burn
• color dodge
• vivid light
• linear light
• hard mix
• difference

Many of your layers contain gradient fill as vector data. Those layers are treated like bitmap layers with blending option "Transparency Shapes Layer"=OFF.

Set layer option "Transparency Shapes Layer"=OFF in your most ordinary layer and see how the grey cloud turns to a bright blueish star

Blending mode Color dodge takes the opacity of the bitmap into the account quite radically differently depending on layer option "Transparency Shapes Layer". OFF causes (I believe so) the wanted effect and ON causes the partially transparent pixels to be like the blending mode is = Normal.

Layer masks also cause transparency, but it doesn't interact with blending mode "Transparency Shapes Layer".

BTW. The last sentence is true also with adjustment layers:

There's curves-layer with a B&W layer mask and blending mode color dodge. I must admit that this is 100% of my knowlwdge about the non-normal blending modes and blending options of the adjustment layers.

Due the previous I believe that Photoshop allows numerous combinations of mode selections which are nonsense or at least not documented. I think that layer blending mode "Transparency Shapes Layer" is intended for layer effects (=Layer Styles) and it treats other transparency in an undocumented way.

Answer 2

Vectors & Bitmaps Calculate Differently with Color Dodge

This is because most of your stars are vectors, while the ones that look different with Color Dodge are bitmaps.

When Photoshop uses its algorithm to calculate the Color Dodge blend mode, it has a lot of information to work with when a vector is used. However, when working with a bitmap, there is limited colour information and the calculation uses a different method.

To give the bitmaps a better chance with Color Dodge, you can swap to CMYK color, which despite being a smaller colour gamut than RGB, it produces better results.

Alternatively, use Advanced Blending Options to give the bitmap Color Dodge calculations a boost.

So the key is, to keep everything consistent. Use only vectors with RGB for the best result.

*Layer Styles and shapes are all vectors.