Mattias Gustavsson, creator of retro projects including DOOM-CRT and Extricatio­n, talks through his CRT Image Viewer (bit.ly/crtview), explaining how it simulates ’80s displays:

CURVATURE “The viewer applies a curvature to the image, to emulate the ways old CRT screens were not flat, which distorted the shape of the image.”

COLOUR CHANNELS “It pulls the red, green and blue colour channels apart ever so slightly, in different directions. CRT screens have little clusters of individual red/green/blue dots with a slight offset. The effect of this can be seen when you, for example, have a large block of white on a black background, and you can see a faint tint of colour on the edges.”

SCANLINES “Probably the effect most associated with CRTs are scanlines. On a real CRT, scanlines are gaps between horizontal rows of pixels, but for my shader I do it just by darkening some pixel lines.”

GHOSTING “It applies a blur trail on top of everything. This is to emulate the way the phosphor of a CRT screen takes a short time to fade out once you turn it off, leaving a bit of visual persistenc­e to moving things, and giving a ghost trail when things move around.”

VIGNETTE “After that, a vignette effect is applied, making the whole screen brighter in the centre and darker towards the edges/corners. On a real CRT, there is an electron gun in the centre, sweeping over the screen surface, and it tends to be brighter towards the centre.”

SHADOW MASK “This emulates the ‘aperture grill’ or ‘shadow mask’ of a CRT, which is a fine metal mesh overlaid on the phosphor dots. I emulate this by just adding vertical lines that darken some of the pixels, just like scanlines, but fainter.”

NOISE “I add a very faint flicker and some faint noise, which you can barely see but which makes the filter feel a bit more alive.”

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