Recently in the design of a Qt control, need to get a picture of a pie, in Photoshop after the discovery of the storage will always take the background, the PNG format after the background is still there, just become transparent. I just found a way to save a single layer and have no background at all on Google.
1. For example, create a new file, use the Ellipse tool to hold down SHIFT and drag the mouse to draw a positive circle, note that the image is grayscale mode, paint bucket is always gray when coloring, you need to change in the image-mode to RGB color mode.
2. Select the ellipse layer in the layers panel and right-click to select Convert to Smart object.
3. Right-click the layer again and select edit content.
4. Effects. You can save it now.
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PS CC 2014 method of outputting a layer as a file