ModRetro Chromatic Frame Blending Comparison
8(WARNING: This video contains rapidly strobing images and may potentially trigger seizures for people with photosensitive epilepsy. Viewer discretion is advised.)
The new ModRetro Chromatic, a handheld FPGA console which simulates a Game Boy Color and plays original Game Boy and Game Boy Color cartridges, has the ability to output video being displayed on its screen to its USB Type-C port while the handheld is being played. When connected to a PC vis USB, the Chromatic shows up as a webcam. Capture software like OBS can capture the video output from the console's USB port. The video is captured at the GBC's native screen resolution, 160x144. I have upscaled the output by 15x, but it is perfectly sharp in its native resolution with no excess color. The accompanying audio must be recorded by the headphone jack if the whole experience is to be captured.
The Chromatic has an interesting 3:1 frame blending mode not seen on the other FPGA handhelds I own, the FPGBC and Analogue Pocket. They use a 2:1 frame blending mode, which usually eliminates flicker. Some games rapidly alternate between two sets of colors for certain objects, relying on the slow response time of the LCD crystals to alter the light's polarization to change the shade or color to give a transparency effect. I believe the Chromatic may be trying to simulate the flicker seen on an original GBC screen, especially with monochrome games. The GBC has faster pixel response times by using a TFT display as opposed to the older STN displays of monochrome systems. I have tried to capture how it can affect the graphics when the mode is turned on and off. I have featured four games, two monochrome, two color, which use the flickering more or less to some intended effect:
0:00 - Chikyuu Kaihou Gun ZAS
1:01 - Serpent
1:50 - 3D Pocket Pool
3:17 - Shantae
Each game is started with the frame blend off, then turned on. The Chromatic's Menu will appear to show when the change occurs.
One thing I want to emphasize is that this flicker does not accurately represent the flicker seen on the Chromatic's screen. There is flicker with the frame blending setting on and off but it is less noticeable on that screen. Also, that screen does not show any frame skipping, at least none that I can perceive, with either setting choice. The Game Boy and Game Boy Color run at a frame rate of 59.7225Hz and the webcam outputs 60Hz, so frames must be duplicated at certain points to make up the difference. What I am trying to show is how the frame blend option works through the capture function and the relative amount of flicker reduction one can expect by turning the option on either with the screen or the webcam's output.
You may notice that the audio is very noisy. This appears from the output when the Chromatic is connected via USB. I had to use my best USB Type-C to Type-C cable from my Analogue Pocket and connect the Chromatic directly to one of my PC motherboard's Type-C ports to get the noise as low as I could. I also tried other audio cables and none improved the noise. The audio is recorded at its maximum volume from the volume wheel and my PC's line input is at its 100% input level. Just before the five minute mark I pull out the USB cable from the Chromatic (which will switch to batteries if in the console) to record audio without the cable's interference. This is why the video stays a static screen at the end.