Transparent gets blended & threshold anomaly

In three of the blend modes, parts that I think are supposed to be transparent seem to still be getting blended. The three modes are: 5-Linear Burn, 9-Linear Dodge, and 13 -Vivid Light. (The attached filter will hopefully help show what I mean...)


Also I noticed when I put threshold to 100% on the lifesaver image, I get a few white splotches where the image should be 100% black. (If it's an error in the image file, then maybe it could be repaired somehow? (Or maybe it's just my image file that's corrupt?))


P.S. I guess the 19-Luminosity mode blends the transparent parts too. (And maybe this transparent blending is intentional?)

alphablend2.ffxml

I just checked in PSP, and the threshold at 100% (255) does keep pure white as white -- I guess that does make sense too.

Since there hasn't been a reply from FF, I thought I'd clarify that those four blend modes (i.e. 5, 9, 13, and 19) still seem to be blending the transparent parts of the mask. The threshold stuff was a different issue -- in case that was unclear...

Vladamir,

Yeah, it makes sense that all the other channels still get calculated...
But (to me) what doesn't seem to make sense is that in four of the Blend Modes, the Foreground's Alpha channel doesn't seem to get calculated/factored in with the final result, but, meanwhile, all the other Blend Modes do seem to include the Alpha channel values with the calculations.


For example:
If the Blend Mode is Linear Light, then the Foreground's Alpha values seem to get calculated in with the Blend component's Opacity values. (In my filter above using a Linear Light mode (14), we seen none of the offset/Foreground image in the final result.)
But with Linear Burn (5) and Linear Dodge (9), only the Blend component's Opacity values seem to get used (and the Foreground's Alpha values get ignored). (So in my filter, here we do see "parts" of the offset/Foreground image in the result.)

Since Linear Light is supposedly, basically a mixture of Linear Burn and Linear Dodge calculations, the Blend modes don't seem to be predictably consistent with each other. I.e. To me it still seems like the discrepancies here are more from an error in the programming, rather than having an intentional purpose behind them.
(BTW, I still respect that FF can be however you guys want it to be. I'm just pointing out how things look to me in case something in the calculations might have gotten overlooked.)

Vladamir,

Actually, I believe Photoshop does factor in the alpha channel of the foreground image with those four blend modes (where my filter in the OP seems to show that FF does not do this).


Here is a test to try in PS to show that the foreground alpha channel does get factored in for those modes:
1. Open some colored image into Photoshop.
2. Duplicate the original image layer so that you have a copied layer above it.
3. Erase part of that duplicated/copy layer (using the Eraser at 100% opacity or select an area and Edit->Cut it out).
4. Adjust the blend mode to be: Linear Burn, Linear Dodge, or Vivid Light.
5. Here you should see that where the parts are transparent in the foreground layer, you see only the original background layer’s colors -- where none of the foreground's blend is shown. (That is, with these blend modes, just like all the other blend modes in PS, the alpha channel of the foreground layer still gets factored into the blend result.)
6. PS's Luminosity blend mode does this too, but you won’t see it unless you do something like offset the foreground layer (e.g. use Filter->Other->Offset on the foreground layer.) And here again, where the parts are 100% transparent on the foreground layer, you see only the original background image.



To try to explain this hopefully even clearer, I made another quick filter that uses each blend mode in 19 presets. (In it I offset the foreground in all of the presets, to be relevant for all the blend modes). You'll see that, different from all the other blend modes, the 5th, 9th, 13th, and 19th blend modes/presets all show the right half as being blended as if the foreground was 0% transparent in that area -- where the modes seem to ignore the foreground’s alpha channel.)
But if you were to set up an equivalent scenario in PS for those four modes, the right half would show 0% of the foreground blend on the right half of the image (as the foreground’s alpha channel seems to get factored in as 100% transparent in that area).

alphablend3.ffxml

I made a PSD file, but am having trouble attaching it here.

First it was too big, so I reduced the image size to very small (so the PSD file size was 122 KB -- but where there's still enough info there to see the idea).

Now I'm getting the error message:
"Incorrect file type or maximum size of the file exceeded (.psd)!" (It's a .PSD, 122 KB file, so I don't know what's wrong now.)

I even clicked on your E-Mail link at the bottom of your post, but didn't see a way to send attachments...

I think is probably related, Set Alpha bleeds through Threshold to Result.

Problem Set Alpha.ffxml