Alpha Channel

[JeremyLangford]

For some reason, I am having trouble understanding the alpha channel. Every time an image such as a GIF or PNG is exported with transparency from photoshop, the image must include an R, G, and B channel as well as an Alpha channel right? (I think this might be different with GIFs because indexed color is used)

Am i right in thinking that even though the image includes an alpha channel, the only channels sent to the monitor are the R, G, and B channels?

[René Damkot]

Yeah. An alpha channel is just like a mask: It shows where transparency is.
http://en.wikipedia.org/wiki/Alpha_channel
http://graphicssoft.about.com/od/photoshop/l/bllps504h.htm
http://blog.lynda.com/2010/01/05/photoshop-top-40-alpha-channels/

[JeremyLangford]

Is this right?

Even though things like alpha channels or CMYK color modes can exist in an image, they have to be calculated out by the video card so that the only thing ever sent to the monitor is a R, G, and B channel which can vary in bit depth depending on the video card and then also the monitor.

I'm hoping that this is a somewhat good explanation of how data is sent to the monitor.

[basroil]

Is this right?

Even though things like alpha channels or CMYK color modes can exist in an image, they have to be calculated out by the video card so that the only thing ever sent to the monitor is a R, G, and B channel which can vary in bit depth depending on the video card and then also the monitor.

I'm hoping that this is a somewhat good explanation of how data is sent to the monitor.
http://en.wikipedia.org/wiki/Digital_Visual_Interface
Then read the external links.
Then read this:
http://www.ddwg.org/lib/dvi_10.pdf

Then find a more specialized forum, since this really isn't set up to solve your questions.

[JeremyLangford]

From those links I learned that the data signal of DVI includes R,G,B data, clock signal data, and a display data channel. I also learned that a single DVI link consists of four twisted pairs of wires (red, green, blue, and clock) to transmit 24 bits per pixel but 48 bits per pixel can be achieved when using dual-link dvi.

As far as I can tell, this information backs up my previous post but I really have no idea if my previous post is correct.

Basroil, I was already planning on not asking more questions in this thread because I think that's what gets me into trouble. I'm trying as hard as I can to learn this stuff on my own but most of it is over my head.

[basroil]

Basroil, I was already planning on not asking more questions in this thread because I think that's what gets me into trouble. I'm trying as hard as I can to learn this stuff on my own but most of it is over my head.

Not that it gets you in trouble, rather that this isn't the best place for you to get the answers you're looking for.

Though you're going about it all the wrong way. Unless you are planning on getting a master's in computer/electrical engineering, it's entirely pointless to even bother understanding more than just the basics.

[woloi]

Not that it gets you in trouble, rather that this isn't the best place for you to get the answers you're looking for.

Though you're going about it all the wrong way. Unless you are planning on getting a master's in computer/electrical engineering, it's entirely pointless to even bother understanding more than just the basics.

I think that there is absolutely nothing wrong in spending some time trying to figure out how something works. Then again, I *DO* have a undergraduate degree in ECE, so I am interested in this kind of thing, and most definitely support other people trying to learn.

Jeremy, what you're saying sounds about right. A picture may consist of any number of color schemes, but the monitor ONLY supports RGB. There's no such thing as a transparent pixel on your monitor. Transparency is virtual, handled by the video card to make a pretty user interface. The video card and image software are also responsible for translating the digital picture information into something the monitor can display.

I'm not familiar with the hardware side of DVI, but I do know single link can only drive up to a certain size, somewhere around 1920x1200, beyond that you need dual link for the extra data capacity.

[JeremyLangford]

I think that there is absolutely nothing wrong in spending some time trying to figure out how something works. Then again, I *DO* have a undergraduate degree in ECE, so I am interested in this kind of thing, and most definitely support other people trying to learn.

Jeremy, what you're saying sounds about right. A picture may consist of any number of color schemes, but the monitor ONLY supports RGB. There's no such thing as a transparent pixel on your monitor. Transparency is virtual, handled by the video card to make a pretty user interface. The video card and image software are also responsible for translating the digital picture information into something the monitor can display.

I'm not familiar with the hardware side of DVI, but I do know single link can only drive up to a certain size, somewhere around 1920x1200, beyond that you need dual link for the extra data capacity.

Thanks. One reason I was confused about this is because if I click on "About this Mac" on my laptop and look at the specs, it says my built in LCD monitor has 32-bit color. The only 32-bit color I am familiar with includes an alpha channel and so I don't see how my monitor could be 32- bit instead of just 24-bit.

[basroil]

Thanks. One reason I was confused about this is because if I click on "About this Mac" on my laptop and look at the specs, it says my built in LCD monitor has 32-bit color. The only 32-bit color I am familiar with includes an alpha channel and so I don't see how my monitor could be 32- bit instead of just 24-bit.

It's not. It runs in 18bit because 99%+ of laptop displays are TN, which run at 6bit/channel.

[woloi]

Thanks. One reason I was confused about this is because if I click on "About this Mac" on my laptop and look at the specs, it says my built in LCD monitor has 32-bit color. The only 32-bit color I am familiar with includes an alpha channel and so I don't see how my monitor could be 32- bit instead of just 24-bit.

Sorry, not familiar with Macs, so I can't really help you there. My guess is you're misreading it and it's "32 bit color" which would include an alpha channel so far as video card rendering is concerned.

[René Damkot]

From http://en.wikipedia.org/wiki/Color_depth#32-bit_color

"32-bit color" is generally a misnomer in regard to display color depth.

;)

[JeremyLangford]

Heres what 'm reading:

NVIDIA GeForce 9400M:

Chipset Model: NVIDIA GeForce 9400M
Type: Display
Bus: PCI
VRAM (Total): 256 MB
Vendor: NVIDIA (0x10de)
Device ID: 0x0863
Revision ID: 0x00b1
ROM Revision: 3427
Displays:

Color LCD:
Resolution: 1280 x 800
Depth: 32-Bit Color
Core Image: Hardware Accelerated
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Built-In: Yes
Display Connector:
Status: No Display Connected