65K-Colour vs. 262K-Colour on Windows Mobile Devices

[Darius Wey]

<div class='os_post_top_link'><a href='http://blogs.msdn.com/windowsmobile/archive/2005/09/07/462187.aspx' target='_blank'>http://blogs.msdn.com/windowsmobile.../07/462187.aspx</a><br /><br /></div><i>"When was the last time you saw a Windows Mobile device that couldn't do color? (It's a trick question. The last grayscale device predates the name change to "Windows Mobile.") Subtle differences in screen quality aside, all WM devices have had the same ability to show colors--65536 of them. Modern LCD screens, however, are capable of showing four times that many (262144). So I've been asked, "Why doesn't WM allow OEMs to make use of these better screens?" The short answer is: "We do." The medium answer is: "But don't be so sure you want them to." And the long answer is ... well the rest of this entry."</i><br /><br />Mike over at the Windows Mobile Team Blog has written up another great article - this time, he focuses on the 65K-colour vs. 262K-colour issue. Obviously, the more the merrier and our eyes thank us for it, but have you ever wondered why the adoption of 262K-colour screens on Pocket PCs and Smartphones has trudged along at a snail's pace? Mike's article has all the information, and you'll soon find out that as far as current technology is concerned, more is less (for the moment, anyway).

[R K]

Unless I'm missing something, 320 x 240 = 76,800 pixels, so anything above 65,536 colors is only going to benefit the remaining 11,264 pixels, which is only a 15% increase in color depth.

Now VGA displays get a bigger benefit since 640 x 480 = 307,200 pixels, but I'm satisfied as it is now if more colors mean GAPI and driver issues.

The color accuracy on the current crop of screens is what's most important though. If you've ever tried viewing photos of people on Pocket PCs, you'll know that 50% of the screens out there don't display human skin and hair accurately enough.

[PDANEWBIE]

Thats fine thinking for a static picture on a screen but in things like PDA's where the pixel color may change depending on the app that is in the forefront having those extra color bits would make it so you don't have any color washout or slowdown of the PDA as it rewrites the color pallets.

At least this is the one drawback I see in the real world scenario with multiple applications running...

Personally I would love to see the more colors but not at any expense to speed or to battery life.

[Menneisyys]

There is another pros/cons thread worth reading here (http://www.pocketpcthoughts.com/forums/viewtopic.php?t=39651).

[alex_kac]

Unless I'm missing something, 320 x 240 = 76,800 pixels, so anything above 65,536 colors is only going to benefit the remaining 11,264 pixels, which is only a 15% increase in color depth.

Now VGA displays get a bigger benefit since 640 x 480 = 307,200 pixels, but I'm satisfied as it is now if more colors mean GAPI and driver issues.

The color accuracy on the current crop of screens is what's most important though. If you've ever tried viewing photos of people on Pocket PCs, you'll know that 50% of the screens out there don't display human skin and hair accurately enough.

It really doesn't matter on the number of pix. What matters is that you can get the depth of color in the bands that you need. Have a pic of a forest - you want more green shades to show.

[badbob001]

Unless I'm missing something, 320 x 240 = 76,800 pixels, so anything above 65,536 colors is only going to benefit the remaining 11,264 pixels, which is only a 15% increase in color depth.

What you just said doesn't really make sense. What does the number of pixels have anything to do with the number of colors? If you buy a larger box of crayons, do you have to buy a larger sheet of paper?

Having more colors allows you to have smoother shades and less dithering. Think of it this way: Windows icons haven't changed much in size over the years but they sure look a lot better given the more colors they can have now. Try this in your windows display properties: Effects > uncheck [ ] Show icons using all possible colors. Looks bad now, huh?

[saru83]

Modern LCD screens, however, are capable of showing four times that many (262144).

Hey DARIUS, i read the article twice, its awesome but there is something weird, basically he mentioned that there isnt any Mobile device with FULL 24bit support yet... but actually there is....

a lil proof:

12bit colour screens is 4096 colours (HINT: 2^bit , ex: 2^12=4096)

16bit colour screens are 65536 ( same as above 2^16=65536)

18bit col...... ..... are 262144

24but ............ ... are 16777216

so basically what i wanna say is that SAMSUNG has released a 16.7 Million colour screen cell phone which is the FULL 24 bit thing...

Any explanation!!??!!

[Wiggster]

Unless I'm missing something, 320 x 240 = 76,800 pixels, so anything above 65,536 colors is only going to benefit the remaining 11,264 pixels, which is only a 15% increase in color depth.
Those two numbers really have nothing to do with each other, it's mere happenstance that they're close to each other.

The color depth refers to the number of colors each pixel can display. Going back to good old CRT days, each color is represented by a specific ratio and intensity of red, green, and blue. The most advanced consumer screen today can display 256 levels of green, 256 levels of red, and 256 levels of blue per pixel. That's 2^8 for each color, so 2^8*2^8*2^8 total combinations. 2^24 = about 16.7 million possible color combinations per pixel. The total number of color combinations for a 240x320 screen with 24 bit color is well over 1 trillion, as each pixel has 16,777,216 combinations. With 16 bit color, that's only 5 billion combinations.

Going from 2 colors to 4 colors is a huge difference. From 16 to 256 is a huge difference. From 256 to 65k colors is a huge difference. Trouble is, from 65k to 16.7 million colors isn't a big difference. It's only noticeable with many slightly-varied similarly colored shades in proximityt to each other. With 16 bit color, you'll notice when colors are clustered together instead of smoothly transitioning from one to the next (banding), easily observable in gradients. But that's about it. If you look at a well-composed color photograph without gradients, 16bit and 24bit color would look nearly identical. Banding isn't noticable in many many situations. And the article linked goes into detail about why taking that additional step from 16bit to 24bit color isn't very memory-efficient, and therefore not worth it.

Modern LCD screens, however, are capable of showing four times that many (262144).


so basically what i wanna say is that SAMSUNG has released a 16.7 Million colour screen cell phone which is the FULL 24 bit thing...

What Darius was saying was that most screens released show 262k colors. I'm sure you'll find that the screen on Samsung's phone isn't used in very many devices. There are tradeoffs in brightness, battery life, and, most importantly, cost to the manufacturer. They need to keep brightness and battery life up while keeping cost down. Problem is, more of the former leads to more of the latter, and the same can be said with color. And more colors means more memory, as the article illustrates.

Do I want a 24 bit display? Yes. Do I want to pay for it? No. Could I notice a difference? Exceedingly easily. Would I notice a difference? Not in casual use. Would I want the performance dip associated with it? Nope.

[Talon]

One minor detail that most people are missing.
You also need a CPU (or graphics chip) that can support 18 bit displays. The XPA25x and 26x parts only supported 16 bits without things getting messy. I'd have to double check if the 27x devices supported them, even then a QVGA screen in 18 bit colour would fit into the internal screen buffer of the 27x parts but you would have to pack the bits giving a hit on graphics speed. If you used 32 bits for each pixel it would run faster but then your screen buffer is to big to fit into the CPUs internal SRAM, putting your screen buffer in system memory slows the whole system down and uses more power.

The display may well be able to support 18 bits but not only is it nastier for the software it just isn't practical on the hardware. You can do it but it would be a case of marketing over logic to do so.

[benyeap]

So after 4 years+, what is Microsoft Windows Mobile team & MSDN has explanation for this?

24-bit color displays had been around for years & Symbian OS had been adopting this long enough.

WM 6.5 ain't mention anything about improving this, while WM 7 also not much news about this as well.