Start with a recognizable silhouette
An ASCII image has far fewer independent picture elements than the source photograph. Each character summarizes a rectangular region, so thin lines, distant faces and small lettering can disappear before a glyph is selected. Begin with a subject that is clearly separated from its background. Crop and simplify the source in an image editor when necessary; this tool preserves the supplied canvas rather than guessing a crop.
Choose 60–100 columns for an initial review. Increase the width only when the new character cells reveal useful details. A 160-column image is harder to read at small display sizes and creates larger animation files. Increasing the PNG pixel scale merely enlarges the same glyph pixels; it does not recover information lost during conversion.
Density is measured in the font you actually export
The built-in alphabet has five drawing columns and seven drawing rows inside a six-pixel-wide cell. The converter counts illuminated pixels in each chosen glyph, sorts the palette and maps image tones to these measured levels. A custom palette is therefore not read as a manually ordered light-to-dark string. Characters with identical ink counts can represent the same tone, and their visual shapes may still feel different.
The selected palette is normalized between its sparsest and densest glyph. Even the densest ASCII character contains gaps. The result is a stylized image, not an exact brightness reproduction. Include a space when the design needs truly empty cells.
Adjust one control at a time
Brightness and contrast affect the sampled linear-light image before gamma and glyph selection. Lift gamma when important midtones vanish. Reduce contrast when both dark and light regions lose detail. Inversion changes character coverage after these adjustments, while the selected theme determines whether dense ink represents light or dark regions.
Error diffusion distributes a cell’s tone mismatch into neighboring cells. This can smooth gradients with a short palette, but it can also create flicker between animation frames because each frame is quantized independently. Compare the result with dithering off before exporting a moving sequence.