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New to photo editing, so I've got some conceptional confusion about the colors and channels,

sample

  1. In photoshop, we can create text layer, we can have text on top of an "empty space" the checker board, then what is the color of the checker board, from what I can see the checker board does not have color information, so what exactly is the empty area?

  2. Photoshop treats the fourth channel as Transparency channel, but even if I do not have this channel I still have Transparency in the empty area, so I can control an area's transparency with transparency channel, or set it to "totally empty", really do not understand the difference between "Empty area" and "Transparency channel" and "Alpha channel"

So when I want to have transparency background, do I need to erease the part that should be transparent, or make a "Transparency channel" or "Alpha channel"?

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  • Technically in the final bitmap format there is no such thing as a transparent pixel. – joojaa Jan 29 at 15:32
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All documents in Photoshop must have a width and a height. If there is a width and a height, but no pixel data, the area is defined as "empty". "Empty area" encompasses the document canvas without pixel data and is used to describe areas between pixel data and the canvas edges.

When exporting/saving Photoshop does not save/export the "empty area".

All "empty areas" are transparent.

enter image description here


Transparency is defined as an area which has no pixel data. No color, no value, nothing. If you want to control transparency in Photoshop, that is done by adding or removing pixel data in Layers or color Channels.

There is no "transparency channel" in Photoshop. The pixel data on layers defines transparency.


An Alpha Channel is a saved selection. Similar to a layer mask, an Alpha channel merely indicates a specific area on the open document. There's some liberty taken by Adobe - using "Alpha" in a more broad sense where customarily "Alpha" has meant transparency.. that's not always the case within Photoshop. Alpha Channel, in Photoshop, merely means "extra".

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  • Hello thanks for replying, I saw your demo image says the text area has pixel data, then what about the area between the letters does it have data as well? – Dew Jan 28 at 11:27
  • the "pixel data area" is going to be the smallest rectangle that can contains image information, often called the "extents." This is a memory optimization, and a layer may actually have two or more areas/extents if they do not overlap (depending on the software). I expect there is some form of "alpha information" stored for these areas. In this way, the non-pixel area is "empty" and the image can be reconstructed by storing the width and height, and the origin point of each pixel-area. instead of storing a full byte per channel per pixel for empty areas. – Yorik Jan 28 at 17:30
  • @Dew As Yorik points out the non-empty area consists of the smallest rectangle which encompasses pixel data. Areas such as those between type glyphs are not considered "empty" but rather simply transparent. All empty areas are transparent, but not all transparent areas are empty. – Scott Jan 28 at 18:23
  • I am use this texture in blender, it treated the empty space as black color so I was wondering what value is stored in this area – Dew Jan 28 at 22:56
  • @Scott After some trials I found that my PNG file's transparent area is R:0,G:0,B:0 and Alpha:0, this is essentially black clolor plus Alpha 0, I'm not sure why. – Dew Jan 30 at 7:48

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