What Is an Alpha Channel

Which formats carry one

The number of levels is what decides whether an edge looks cut out or looks glued on. One bit is the reason nobody misses GIF for this.

Why the values in between are the whole point

If transparency were only on or off, every edge would be a staircase. Real edges are not aligned to the pixel grid, and a single strand of hair is thinner than a pixel is wide, so the pixel it falls in is genuinely part hair and part whatever was behind it. An alpha value of thirty percent there is not a compromise or a rounding. It is what the camera recorded.

That is the difference between a cutout that keeps hair and one that produces a shrink wrapped silhouette: whether the edge pixels were allowed to be partial or were forced to pick a side.

Why your PNG has a black background

Almost always because the image passed through something with no alpha channel, which had to put a colour where the transparency used to be. JPEG is the usual culprit. The colour is usually white, and it is black often enough that this is the question people arrive with.

The other cause is the viewer rather than the file. Some preview panes and some older programs draw transparent areas as black instead of as a checkerboard. Open the same file in a browser before deciding the file is broken.

The checkerboard is a drawing, not data

The grey and white squares behind a transparent image are drawn by whatever you are viewing it in, so that you can tell transparent from white. They are not in the file and they do not export.

They are also a poor way to inspect a cutout. Light grey hides pale halos, which is the most common defect there is. Put the cutout on a saturated colour instead, red or black, and a halo announces itself immediately.

Keeping it all the way to the end

Save as PNG or WebP. Save as JPEG and the alpha is gone permanently rather than hidden. If some service insists on JPEG, choose the background colour deliberately instead of letting it default, so the result is the one you picked.

If you wanted a coloured background anyway, filling one is a separate step that runs on your own machine and sends nothing anywhere.

Getting a cutout with a real alpha channel

The background remover here returns a PNG with a full alpha channel, hair and soft edges included. It is one of the three tools on this site that do send your file to our servers, and that is worth saying plainly rather than blurring: the image is processed and dropped, never stored, and never used to train anything.

More guides

• The Transparent PNGMaking one is the easy half. Keeping it transparent all the way to wherever it is going is the other half.

FAQ

What is an alpha channel?

A fourth value stored with every pixel alongside red, green and blue, describing how opaque that pixel is. Zero is fully transparent, the maximum is fully solid, and the values in between are what makes a soft edge possible.

Which image formats support transparency?

PNG, WebP and AVIF carry a full alpha channel. GIF has one bit of it, so a pixel is either there or not. JPEG has none at all.

Why does my transparent PNG have a black background?

Either it passed through a format with no alpha, most often JPEG, and the transparency was filled in, or you are viewing it in software that draws transparent areas as black. Open it in a browser to tell those two apart.

Does saving as JPEG remove transparency?

Yes, permanently. Every transparent pixel is written out as a solid colour, and reopening the file cannot recover what the alpha channel said.

Is transparency the same as a white background?

No, and the difference shows the moment the image is placed on anything else. A white background stays white on a dark page. A transparent one takes the colour of whatever is behind it.

What is premultiplied alpha?

A storage convention where the colour channels have already been multiplied by the alpha value. It makes compositing cheaper and it is mostly a concern inside software rather than in the files you handle. A dark fringe on a cutout placed over a light background is one thing a mismatch here can cause.