Is there a concise and accurate discription of how Blend If functions?

Forum|Forum|29 days ago
March 11, 2026
4 replies
130 views

Even the Adobe docs under: https://helpx.adobe.com/photoshop/using/layer-opacity-blending.html are not very good. AFAiCT Blend If does one thing and one thing only; it changes the Transparency of the pixels in the upper layer. I tried Gemini AI and it returns a short and completely wrong answer.

Correct answer D Fosse

@TimInSeattle

On the face of it, it’s straightforward. Pixels in the current layer are rendered transparent, revealing the underlying layer, based on the values in either current or underlying layer.

You can split the sliders with the Alt key for a tapering gradual onset:

So far it’s pretty basic. However, it gets really interesting and useful when you use Blend If per channel. Look at the green channel in this image, and how you can specifically target those purples with Blend If on, say, an adjustment layer:

Stephen Marsh

Community Expert

Here’s the article, ah, 25 years in the blink of an eye!

https://web.archive.org/web/20100116171247fw_/http://members.ozemail.com.au/~binaryfx/blendif.html

https://web.archive.org/web/20101205085110fw_/http://members.ozemail.com.au/%7Ebinaryfx/blendif.html

T

TimInSeattleAuthor

Participating Frequently

thanx Stephen!

I think i understand it pretty well now. Blend IF is only setting the transparency of the Current Layer based on tones in the upper and lower layers. I get lost when i see descriptions like “All pixels with the luminosity value of 0 will be blended as transparent,” What does that mean???

What does blended and unblended mean in PS parlance?

Cheers

Tim

PS - did you know that those two links point to the same article?

Stephen Marsh

Community Expert

Yes, I know that both links point to the same article. As I wrote that article around 25 years ago and the site no longer exists, it can be hard to find working links. If one link goes down, perhaps the other will work!

Stephen Marsh

Community Expert

Blend If is one of those functions that may initially seem simple, however, it’s rather nuanced and much deeper than casual use might suggest.

Many years ago I started a series of articles on my old personal website and only scratched the surface on 1 of 3 intended articles.

A

AKS666

Inspiring

Look on youtube, Photoshop Training Channel and PixImperfect had this covered pretty well.

D Fosse

Community Expert

First of all, do not confuse Blend If and Blend Modes, those two are unrelated. The thread title says Blend If, but you have looked up Blend Modes. Yes, I can see it’s easy to think they’re the same thing.

Blend if just sets pixels to transparent above or below a certain value or value range.

Blend modes are more complex. They calculate a pixel’s RGB values based on the relationship between the RGB values of the current layer, and the RGB values of the underlying layer. Each blend mode uses a different formula for this calculation.

There is no transparency in a Blend Mode, just a numerical calculation and a resulting RGB value. A Blend Mode only exists as a relationship between layers, it does not exist in a single layer.