Why image sharp with white background, but blocky with transparent one?

Question

I'm trying to do something for work that should be very simple, but it's turning out to be far more complicated than I had hoped. I have a jpeg of a Japanese kanji on a white background. I need to have the black kanji without the white background.

I've checked and tried everything I can think of for removing the background. I have used Krita, Photoshop, Illustrator, Fireworks... One of two things happens:

a) The program CANNOT differentiate between the white and black areas of the original jpeg using magic wand, convert colour space, etc.

b) The program CAN differentiate between them, but even with feathering selection and refine edges in PS, the resulting image is blocky, pixellated and has grey squares around it. The kanji in the original image with a white background has sharp, smooth edges and there is no grey.

Here are the two kanji compared in Illustrator. With the right image, I used PS, quick selection tool and refined the edges to attempt to remove the blockiness. (Following this older post: Photoshop: How to make background transparent without affecting image quality?) I need it to have a transparent background, but have edges as smooth and as crisp as they are in the original. I just have no idea what else to try...

Please try to keep your suggestions limited to the programs I have mentioned unless you really think it is impossible to do without acquiring something else.

Answer 1

Your example image on the right is simply low resolution. It may look better at higher resolution. Illustrator should definitely be capable of this.

In Photoshop, you can try using a luminosity mask—i.e. go to the Channels panel and Ctrl+click the composite (RGB) channel. While the selection is active, you can toggle Quick Mask mode to use sharpening filters, or adjustments to increase contrast.

You can then create a solid color fill layer (Layer > New Fill Layer > Solid Color) in black, which will use the selection as its layer mask. You can then make the original layer transparent and export (or "Save for Web") to PNG-24.

For more crispness, you can convert the selection to a work path (Paths panel), and then add the solid black layer; the work path will now become the layer's vector mask. You may get better results by scaling up the image before making the selection, or holding Alt while using the "Make Work Path" command to specify a smaller tolerance value.

For the best results in your specific case, just use the 門 character with a suitable font. I can't identify the font, but there should be a decent font already installed on your OS. (Google Translate can be helpful in finding characters by drawing them.)

Answer 2

Just open the image in Illustrator and go to Window > Image Trace...

Then choose 'Silhouettes' as the preset and make sure that 'Ignore White' is checked:

Done...

Save it as PNG-24 (File > Export > Save for Web)

Answer 3

Good choice of username! I think the issue here is that you are trying to remove the "background" from a raster image - this is always going to lead to dodgy edges. It also appears to have been exported at a low resolution.

If this is a one-off or one of a few, then I would be tempted to trace the kanji manually as a vector in Illustrator, then export that with a transparent background. You can then size/scale as required without iffy edges or aliasing.