Color Flickering

[+Karl G]

How often is color flickering used to make distinct colors in games? E.g. "mixing" the ball, M0, and M1 every other frame to have them be distinct colors from P0, P1, and the playfield. Does this usually work well, or do some find it distracting? I would think it would be less noticeable than flickering objects on and off.

[+Andrew Davie]

49 minutes ago, Karl G said:

How often is color flickering used to make distinct colors in games? E.g. "mixing" the ball, M0, and M1 every other frame to have them be distinct colors from P0, P1, and the playfield. Does this usually work well, or do some find it distracting? I would think it would be less noticeable than flickering objects on and off.

I used it quite a bit in demos in the early 2000's -- for example, look for the 4K mario demo.

The way I do it, ChronoColour(TM), uses three colours on three scanlines. On every frame, the colours and on/of pixels are rolled, so the effect to the eye is a sort of rolling shimmer, rather than flicker.

I also recently used this in my CDFJ Chess demo, which does full-screen playfield colour "flicker".

It looks worse in Stella, because that emulator can't easily reproduce exactly what you see on a CRT TV, where the technique works best.

If you use Stella to view demos, turn on phosphor blending to 30% or more.

 

[+Andrew Davie]

The DPC+ Zaxxon demo uses the same technique. It's remarkable... if you haven't seen it, you should definitely have a look-see.

 

[Just Jeff]

I feel a 1 clock object with similar luminosity is undetectable.  On the other end on of the scale- an 8 clock object flickering black and white is.  What colors and clocks are you using?

[Thomas Jentzsch]

1 hour ago, Karl G said:

How often is color flickering used to make distinct colors in games? E.g. "mixing" the ball, M0, and M1 every other frame to have them be distinct colors from P0, P1, and the playfield. Does this usually work well, or do some find it distracting? I would think it would be less noticeable than flickering objects on and off.

The helicopter in Robot City is done from a missile, flickering between two tank colors. 

[+SpiceWare]

I used it in Medieval Mayhem. I originally implemented it because the dead players get recolored black so their king disappears, but that caused whatever fireball was drawn with that matching player to become invisible:

 

; start of fireball swap routines, used to flicker colors so a fireball
; drawn by a dead king's missile won't be invisible
        lda M0xPosHigh
        ldx M1xPosHigh
        ldy BLxPosHigh

        stx M0xPosHigh
        sty M1xPosHigh
        sta BLxPosHigh
...
 repeat for M_xPosLow, M_yPosHigh, M_yPosLow, M_DirSpeed, M_State, and M_CatchTimer

 

  I liked the shimmering effect it created, so I used it in the DPC+ version of Frantic as well (emphasis added):

Quote

Shots are drawn round-robin so each shot will be drawn using the ball, missile 0 and missile 1 over subsequent frames before being drawn with the ball again. This way if a horizontal shot lines up with a dark color on a robot, it won't be hard to see on every single frame. It also gives the shots a "flickering energy" appearance.

 

The CDFJ version of Frantic has a more advanced kernel that supports missile & ball reuse, so it no longer does that.

[+Karl G]

1 hour ago, Just Jeff said:

I feel a 1 clock object with similar luminosity is undetectable.  On the other end on of the scale- an 8 clock object flickering black and white is.  What colors and clocks are you using?

Right now I'm using COLUP0=$4A, COLUP1=$CA, and COLUPF=$8A. The missiles and ball are flickered every other frame, so one alternates between M0 and M1, one between M0 and Ball, and the last between M1 and Ball. I'm interested in any suggestions on suggested good colors to use for mixing.

 

 

 

chaser.bin

[Just Jeff]

Little tip:  Stella shows extra flicker with odd frame rates.  Get your scanline count to 262 and the prominent flicker you see will go away.  I think it might be fine after that.

[+ZeroPage Homebrew]

Lady Bug Arcade we played last night uses 30Hz flicker colour blending for all the dots in the maze and I didn't even notice until John said it!

The green and purple combine excellently to white! I think it can be used quite effectively with the right colours.

- James

 

 

ZOOMED: WITH PHOSPHOR ON

 

 

ZOOMED: ONE FRAME

 

 

Edited February 14, 2021 by ZeroPage Homebrew

[+Karl G]

1 hour ago, Just Jeff said:

Little tip:  Stella shows extra flicker with odd frame rates.  Get your scanline count to 262 and the prominent flicker you see will go away.  I think it might be fine after that.

Ahh, good to know. I put in some filler lines, and it does indeed look better under Stella.

[Thomas Jentzsch]

6 hours ago, ZeroPage Homebrew said:

ZOOMED: WITH PHOSPHOR ON

That looks like hefty phosphor. Which values are you using?

[CapitanClassic]

16 hours ago, Thomas Jentzsch said:

The helicopter in Robot City is done from a missile, flickering between two tank colors. 

I would say the flicker is barely noticeable. Didn’t even realize the Helicopter was made up of two different colors and that it’s “true” color was the blending of two different colors over two frames.

 

Without looking into it, I assumed the helicopter was made up of a missile, but I assumed the color was changed to a single “helicopter-color” that was different than the tanks on the fly. I would have guessed if two tanks and the heli were on the same line that flicker would have to be introduced, but from the sound of it, flicker may only be necessary if there were 3 tanks and the heli on the same horizontal scanline . With just 2 tanks and the heli, only “shimmer” would occur.

 

This has piqued my interest. I need to look at it more closely is Stella (both with/(out) Phosphor mode on).

[Thomas Jentzsch]

20 minutes ago, CapitanClassic said:

I would have guessed if two tanks and the heli were on the same line that flicker would have to be introduced, but from the sound of it, flicker may only be necessary if there were 3 tanks and the heli on the same horizontal scanline . With just 2 tanks and the heli, only “shimmer” would occur.

It is even simpler.  The tanks constantly flicker at 30Hz, so the flicker is constant in any situation.

 

Remember, the kernel was originally designed for an 1K game where there is not enough ROM space for any elaborate flickering. And since it worked very well, I decided to keep the kernel and invest the bytes somewhere else.

Edited February 14, 2021 by Thomas Jentzsch

[+ZeroPage Homebrew]

13 hours ago, Thomas Jentzsch said:

That looks like hefty phosphor. Which values are you using?

I had to crank it up to 100 in the screenshot to make it match close to the blending of the two colours I was seeing with my eyes.

 

- James

[+Andrew Davie]

4 hours ago, ZeroPage Homebrew said:

I had to crank it up to 100 in the screenshot to make it match close to the blending of the two colours I was seeing with my eyes.

 

- James

Your eyes must malfunctioning from playing way too many games. Didn't your parents warn you this would happen? I asked a while back and was told by a few that about 30% seems to be the figure at which phosphor blend on Stella matches what they see on their TV.

 

[CapitanClassic]

2 hours ago, Andrew Davie said:

Your eyes must malfunctioning from playing way too many games. Didn't your parents warn you this would happen? I asked a while back and was told by a few that about 30% seems to be the figure at which phosphor blend on Stella matches what they see on their TV.

 

I love Stella, but you gotta love the visual streaking caused by sprites on a real CRT from a real Atari, (or AFB2). While playing in the high score club last season, Circus Atari just wasnt the same without the real TV (Partially due to my lack of a Stella Adapter, but also because the clowns were easier to track on the CRT )

[Thomas Jentzsch]

5 hours ago, Andrew Davie said:

Your eyes must malfunctioning from playing way too many games. Didn't your parents warn you this would happen? I asked a while back and was told by a few that about 30% seems to be the figure at which phosphor blend on Stella matches what they see on their TV.

If anything would be malfunctioning, then it would be James' brain. I hope you are not assuming this?  

 

The human brain is blending fast flickering pictures, but it doesn't do that for static ones. So the phosphor effect works only on the former (the optimal blend value depends on the user and the display). For the latter you need way higher values to achieve a similar result.

Edited February 15, 2021 by Thomas Jentzsch

[+ZeroPage Homebrew]

20 hours ago, Andrew Davie said:

Your eyes must malfunctioning from playing way too many games. Didn't your parents warn you this would happen? I asked a while back and was told by a few that about 30% seems to be the figure at which phosphor blend on Stella matches what they see on their TV.

 

It may be true that my eyes have degraded from too many video games, but I'll never let that stop me.

 

Keep in mind these single frame screencaps don't reflect reality and are only to simulate what I'm experiencing with my eyes. Here's zoomed in screencaps at 0%, 50%, 75%, 95% and 100% phosphor settings. The screencap with Stella at 100% most closely reflects what I'm seeing on the screen with my eyes with Stella set to 50% (my normal setting). Only at very near to 100% phosphor setting does the screencap function capture the blend of the two colours to a satisfactory level.

 

Even at 95% I can see slight banding of green and purple in the white dots on the screenshot. I would never see this banding in real life as these would be flashing back and forth between green above and purple below to purple above and green below every 60th of a second. This is all working as I'm sure it's intended with Stella as 100% of green + 95% of purple + 95% of 95% of green + etc... is going to give a slight green hue to the white and vice versa each alternating frame.

 

Just as a point of interest, I normally take two frames at 30Hz (or 3 @ 20Hz) from Stella and combine them in Photoshop rather than use phosphor, much better results for clean screencaps. ? See last photo for an example.

 

- James

 

Single Frame Screencap of Stella @ 0% for Lady Bug Arcade:

 

Single Frame Screencap of Stella @ 50% for Lady Bug Arcade:

 

Single Frame Screencap of Stella @ 75% for Lady Bug Arcade:

 

Single Frame Screencap of Stella @ 95% for Lady Bug Arcade:

 

Single Frame Screencap of Stella @ 100% for Lady Bug Arcade:

Two Single Frames Combined In Photoshop:

 

Edited February 15, 2021 by ZeroPage Homebrew

[+Andrew Davie]

3 hours ago, ZeroPage Homebrew said:

 

Only at very near to 100% phosphor setting does the screencap function capture the blend of the two colours to a satisfactory level

I guess there's a difference between screencap, then, and what the eye sees. And possibly/certainly between two colour interlacing and three colour.

In my CDFJChess, for example, I asked and the consensus was that stella at 30% phosphor was visually the same as the CRT TV.

Would you agree with that, or is it also a matter of "nearly 100%" with that, too?

 

PS: I think "100%" exactly is unusable and gives bogus results because your previous images are simply overlaid with new ones and never disappear.

 

[+ZeroPage Homebrew]

2 hours ago, Andrew Davie said:

I guess there's a difference between screencap, then, and what the eye sees. And possibly/certainly between two colour interlacing and three colour.

In my CDFJChess, for example, I asked and the consensus was that stella at 30% phosphor was visually the same as the CRT TV.

Would you agree with that, or is it also a matter of "nearly 100%" with that, too?

 

PS: I think "100%" exactly is unusable and gives bogus results because your previous images are simply overlaid with new ones and never disappear.

 

 

I completely agree, 100% is completely unusable and unplayable as a setting and I only used it because screencaps are taken in an instant and I wanted multiple frames to blend together.

 

Your recommended setting of 30% on Stella looks great and I've reduced my phosphor down from 50% to 30%.

 

- James

Edited February 16, 2021 by ZeroPage Homebrew