How to get rid black border around object in Photoshop?

Question

I want to put red background (layer 2) on my green object (layer 1). It all looks smooth but after I save as PNG or JPG, black border appears around my green object. How do I get rid of this black border ?

PS. In my photoshop screenshot below, it looks like there's black border too. But in real there's no black border. Image size is 900x900 pixel. I need to use the picture for image processing later so I can't have any other color except for my red & green value.

What I have tried but still fail :

1. Save as PNG
2. Save for Web and Devices in PNG24
3. Save for Web and Devices in PNG2 & unchecked transparency option
4. Flatten the image before export to PNG
5. Try to change to color mode into Indexed color and then export it

→ Here's the file.

Zoom :

This picture from the photoshop window is taken with my phone. Zoomed in 1400% and the edges are still sharp.

Answer 1

I have downloaded your file, and tried to save it in the five ways you mention. I can't reproduce the problem.

The black border you are experiencing must come from scaling the image.

Are you sure that the image you save is the exact same size as the original psd?

If you are sure of the dimensions, then where are you opening the resulting image?

If you open it in a web browser and zoom in, the browser will scale the image using bicubic interpolation by default, which will cause a blurred edge.

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EDIT:

In your screenshot it is obvious that the image has been upscaled.

Your original image is aliased with jagged edges and only red and green pixels. In the screenshot there is about 30 pixels of intermediate tones for 1 original pixel. There isn't just a "black border" - the image has been upscaled using some kind of bicubic interpolation. Since you are sure that it doesn't happen in Photoshop it must happen when you upload or manipulate the image in Picasa. When and how, I can't know (maybe you are applying the image to a larger image and Picasa automatically resizes the image?). I don't understand why you want/need to do image processing in Picasa, when you have access to Photoshop though.

Answer 2

I just got the answer. Thanks for nayhem_jr, original post on Reddit here.

• Export the image using Save for Web and Devices
• Make sure the image scaling is at 100%, because unwanted color values will appear due to interpolation. I should save the image at 100% scaling. (My default was also 100%)
• Then this, Choose Quality = Nearest Neighbor (my default setting was Bicubic)

This works like a charm ! The black lines aren't there anymore.