How do C algorithms convert images to ASCII art using pixel intensity and character fitting?

Image to ASCII Art Conversion in C

Pixel Intensity Based Approach

This method treats each pixel as a single dot. It calculates the average grayscale intensity of the dot and maps it to a corresponding character with similar intensity. A precomputed character map is used for this purpose.

1. Divide the image into pixel or area dots.
2. Calculate the intensity of each dot.
3. Replace the dot with a character from the character map that matches its intensity.

A linear distribution of intensities allows for direct mapping from intensity to character. For a more arbitrary distribution, binary search or minimum distance search is required.

Character Fitting Approach

This method aims to replace areas (rectangular) with characters of similar intensity and shape. It yields better results but is slower than the previous approach.

1. Divide the image into areas with the same aspect ratio as the target font characters.
2. For each area, calculate the intensity in the same way as in the previous approach.
3. Subdivide each character into zones (left, right, up, down, center) and calculate their respective intensities.
4. Find the area with the closest intensity and shape match.

VCL-Based Code

The provided VCL-based code demonstrates both approaches. It includes functions bmp2txt_small for pixel-sized areas and bmp2txt_big for character-sized areas.

Comparison

The character fitting approach produces visually pleasing results, even with larger fonts. It preserves more details due to the shape-sensitive fitting.

In the provided comparison, images marked with green dots are processed with the character fitting approach, while those with red dots are converted using the pixel intensity method.

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