add transparent_bg option

readme.md

@@ -51,7 +51,6 @@ run the program with the following options (the default zig install directory is
    - `-e, --detect_edges`: enable edge detection (optional)
    - `    --sigma1 <float>`: set the sigma1 value for DoG filter (optional, default: 0.3)
    - `    --sigma2 <float>`: set the sigma2 value for DoG filter (optional, default: 1.0)
-   - `    --dither floydstein`: enable dithering (currently only supports floydstein algorithm)
    - `-b, --brightness_boost <float>`: increase/decrease perceived brightness (optional, default: 1.0)
    advanced options:
    - `    --full_characters`: Uses all ascii characters in generated output.
@@ -63,6 +62,10 @@ run the program with the following options (the default zig install directory is
    - `    --keep_audio`: Preserves audio from input video.
    - `    --stretched`: Resizes media to fit terminal window
    - `-f, --frame_rate`: Target frame rate for video output (default: matches input fps)
+   - `-d, --dither <str>`: Dithering, supported values: "floydstein" (default: "floydstein")
+   - `    --fg <str>`: Set a 6-digit hex value like "#ffffff" for the foreground color (default: "#d36a6f")
+   - `    --bg <str>`: Set a 6-digit hex value like "#000000" for the background color (default: "#15091b")
+   - `    --transparent_bg`: Set the background to transparent
 
 >To render on the terminal directly, just omit the output option.
 

src/core.zig

@@ -58,6 +58,7 @@ pub const CoreParams = struct {
     dither: ?DitherType,
     bg_color: ?[3]u8,
     fg_color: ?[3]u8,
+    transparent_bg: bool,
 
     pub fn deinit(self: *CoreParams) void {
         var it = self.ffmpeg_options.iterator();
@@ -505,11 +506,12 @@ fn convertToAscii(
     color: [3]u8,
     block_size: u8,
     color_enabled: bool,
+    channels: u8,
     args: CoreParams,
 ) !void {
     const bm = &(try bitmap.getCharSet(ascii_char));
     const block_w = @min(block_size, w - x);
-    const block_h = @min(block_size, img.len / (w * 3) - y);
+    const block_h = @min(block_size, h - y);
 
     // Define new colors
     const background_color = if (args.bg_color != null) args.bg_color.? else [3]u8{ 21, 9, 27 }; // Blackcurrant
@@ -523,7 +525,7 @@ fn convertToAscii(
             const img_y = y + dy;
 
             if (img_x < w and img_y < h) {
-                const idx = (img_y * w + img_x) * 3;
+                const idx = (img_y * w + img_x) * channels;
                 const shift: u3 = @intCast(7 - dx);
                 const bit: u8 = @as(u8, 1) << shift;
                 if ((bm[dy] & bit) != 0) {
@@ -537,17 +539,13 @@ fn convertToAscii(
                         img[idx + 1] = text_color[1];
                         img[idx + 2] = text_color[2];
                     }
-                } else {
-                    // not a character pixel: set to black
-                    if (color_enabled) {
-                        img[idx] = 0;
-                        img[idx + 1] = 0;
-                        img[idx + 2] = 0;
-                    } else {
-                        img[idx] = background_color[0];
-                        img[idx + 1] = background_color[1];
-                        img[idx + 2] = background_color[2];
+                    if (channels == 4) {
+                        img[idx + 3] = 255;
                     }
+                } else if (!color_enabled) {
+                    img[idx] = background_color[0];
+                    img[idx + 1] = background_color[1];
+                    img[idx + 2] = background_color[2];
                 }
             }
         }
@@ -582,7 +580,8 @@ pub fn generateAsciiArt(
     if (curr_ditherr) |buf| @memset(buf, 0);
     if (next_ditherr) |buf| @memset(buf, 0);
 
-    const ascii_img = try allocator.alloc(u8, out_w * out_h * 3);
+    const channels: u8 = if (args.transparent_bg) 4 else 3;
+    const ascii_img = try allocator.alloc(u8, out_w * out_h * channels);
     @memset(ascii_img, 0);
 
     var y: usize = 0;
@@ -621,7 +620,7 @@ pub fn generateAsciiArt(
             const ascii_char = selectAsciiChar(block_info, args);
             const avg_color = calculateAverageColor(block_info, args);
 
-            try convertToAscii(ascii_img, out_w, out_h, x, y, ascii_char, avg_color, args.block_size, args.color, args);
+            try convertToAscii(ascii_img, out_w, out_h, x, y, ascii_char, avg_color, args.block_size, args.color, channels, args);
         }
 
         if (curr_ditherr != null and next_ditherr != null) {

src/image.zig

@@ -218,21 +218,20 @@ fn saveOutputImage(ascii_img: []u8, img: core.Image, args: core.CoreParams) !voi
 
     out_w = @max(out_w, 1);
     out_h = @max(out_h, 1);
-
+    const channels: u8 = if (args.transparent_bg) 4 else 3;
     const save_result = stb.stbi_write_png(
         @ptrCast(args.output.?.ptr),
         @intCast(out_w),
         @intCast(out_h),
-        @intCast(img.channels),
+        channels,
         @ptrCast(ascii_img.ptr),
-        @intCast(out_w * 3),
+        @intCast(out_w * channels),
     );
     if (save_result == 0) {
         std.debug.print("Error writing output image\n", .{});
         return error.ImageWriteFailed;
     }
 }
-
 pub fn processImage(allocator: std.mem.Allocator, args: core.CoreParams) !void {
     const original_img = try loadAndScaleImage(allocator, args);
 

src/main.zig

@@ -39,8 +39,9 @@ fn parseArgs(allocator: std.mem.Allocator) !core.CoreParams {
         \\    --stretched                Resizes media to fit terminal window
         \\-f, --frame_rate <f32>         Target frame rate for video output (default: matches input fps)
         \\-d, --dither <str>             Dithering, supported values: "floydstein" (default: "floydstein")
-        \\    --fg <str>                 Enter a hex value like "#ffffff" for the foreground color (default: "#d36a6f")
-        \\    --bg <str>                 Enter a hex value like "#000000" for the background color (default: "#15091b")
+        \\    --fg <str>                 Enter a 6-digit hex value like "#ffffff" for the foreground color (default: "#d36a6f")
+        \\    --bg <str>                 Enter a 6-digit hex value like "#000000" for the background color (default: "#15091b")
+        \\    --transparent_bg           Set the background to transparent
         \\<str>...
     );
 
@@ -160,6 +161,7 @@ fn parseArgs(allocator: std.mem.Allocator) !core.CoreParams {
         .dither = dither,
         .fg_color = fg_color,
         .bg_color = bg_color,
+        .transparent_bg = res.args.transparent_bg != 0,
     };
 }
 

src/tests.zig

@@ -106,6 +106,7 @@ test "text" {
         .bg_color = null,
         .fg_color = null,
         .threshold_disabled = false,
+        .transparent_bg = false,
     };
 
     const ascii_txt = try image.generateAsciiTxt(allocator, img, null, args);