Answered

Lock Sign Issue

Forum|Forum|8 months ago
September 7, 2025
3 replies
476 views

What is the reason JPG comes with a lock sign? PNG does not come.

Windows

Correct answer jane-e

Adding a little history to Dave's correct reply, Photoshop used to require a Background layer, which is a unique layer that could not be deleted, renamed, reordered, or have transparency.

Background layers have not been required since Alvy Ray Smith came up with the formula for transparency:

"αA + (1-α)B"

and in 1999 Photoshop 5.5 was released. Details here:

https://www.cs.princeton.edu/courses/archive/spring05/cos426/papers/smith95c.pdf

Jane

MahaB82AAuthor

Thanks for all

Glenn 8675309

Legend

just click on the lock to be able to do stuff to that image.

davescm

Community Expert

It indicates a background layer, which is a specific type of layer that cannot be transparent. That matches the file it came from as a jpeg cannot contain transparency either.

A png can contain transparency, so opens as an ordinary layer - Layer 0.

You can convert a background layer to an ordinary layer, but remember if you make any pixels transparent then that will not be supported in a jpeg.

Dave

MahaB82AAuthor

Is there any special usage for layers without transperency?

MahaB82AAuthor

No. They were required through PS 5.0 (not CS5.0). JPEGs still require a Background layer, but otherwise they are unnecessary.

Jane

My question is incorrect. I use PNG layer often, if there is no need for background image. But I am not clear about JPG layer. Today I watched a video, video shows about using Leves & Curves. Presenter used JPG layer. I wish to know is there any special purpose of using JPG layer?

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