How to handle the transparency of the PNG file with Levels?

Forum|Forum|8 years ago
July 17, 2017
2 replies
1304 views

I need to apply the effect Levels or Curves to the alpha channel of the PNG file.

How can I do it?

As in After Effects

There is no such thing in Photoshop.

This topic has been closed for replies.

Correct answer davescm

When you open a PNG - Photoshop uses the alpha information to create transparency on a single layer rather than the layer with a mask (i.e. separate alpha)

No problem just do the following:

1. Open the PNG

2. Click on the layer

3. Go to menu Layer - Layer Mask - from Transparency

4. You now have the alpha channel as a separate channel that you turn on in the channels panel and use levels /curves to adjust

Dave

davescm

Correct answer

Community Expert

When you open a PNG - Photoshop uses the alpha information to create transparency on a single layer rather than the layer with a mask (i.e. separate alpha)

No problem just do the following:

1. Open the PNG

2. Click on the layer

3. Go to menu Layer - Layer Mask - from Transparency

4. You now have the alpha channel as a separate channel that you turn on in the channels panel and use levels /curves to adjust

Dave

R

r2-no-d2Author

Inspiring

Thanks, it works.

davescm

Community Expert

Just resave with the adjusted mask.

There is a caveat however. The success depends on how the transparency with which previous file was saved.

When Photoshop exports a PNG, for some large areas* where the transparency layer is zero i.e. fully transparent - then the image information on the RGB layers is not saved. Those pixels are filled with white. I presume this is done to reduce the file size on saving PNG (pointless saving RGB channel info which will never be displayed).

You can prove this. I exported two identical images each with a mask which is white in a small rectangle. In the first the remainder of the mask was black (i.e. transparent), in the second the remainder of the mask was L value 1 =RGB6 .

The first file size is 5.71MB the second. with only a small change from fully transparent to partially transparent, leaps 22.1MB. That second size remains for any other value of the mask up to 100%. The increase represents those image pixels which need to be shown (therefore saved) once the transparency is above 0

*How large an area and what "rules" lead to this I am not sure but you can see it where whole edges are transparent.

Dave