From c9228ffa367405907265fc96228e7bf046ff7f11 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rosehogenson@posteo.net>
Date: Thu, 28 May 2026 13:12:58 -0700
Subject: Fix transparency for block24

---
 thumbnailer.go | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/thumbnailer.go b/thumbnailer.go
index 6c69fc1..c0d7c9e 100644
--- a/thumbnailer.go
+++ b/thumbnailer.go
@@ -179,10 +179,7 @@ func printImgXterm(w io.Writer, img image.Image) {
 		for x := 0; x < img.Bounds().Dx(); x++ {
 			hi := img.At(x, y)
 			if hi == color.Transparent {
-				if x > 0 && img.At(x-1, y) != color.Transparent {
-					fmt.Fprint(w, "\033[49m")
-				}
-				fmt.Fprint(w, " ")
+				fmt.Fprint(w, "\033[49m ")
 			} else {
 				lo := 9
 				if y+1 < img.Bounds().Dy() && img.At(x, y+1) != color.Transparent {
@@ -195,6 +192,11 @@ func printImgXterm(w io.Writer, img image.Image) {
 	}
 }
 
+func isFullyTransparent(c color.Color) bool {
+	_, _, _, a := c.RGBA()
+	return a == 0
+}
+
 func printImgBlock24(w io.Writer, img image.Image) {
 	for y := 0; y < img.Bounds().Dy(); y += 2 {
 		if y > 0 {
@@ -202,13 +204,10 @@ func printImgBlock24(w io.Writer, img image.Image) {
 		}
 		for x := 0; x < img.Bounds().Dx(); x++ {
 			hi := img.At(x, y)
-			if hi == color.Transparent {
-				if x > 0 && img.At(x-1, y) != color.Transparent {
-					fmt.Fprint(w, "\033[49m")
-				}
-				fmt.Fprint(w, " ")
+			if isFullyTransparent(hi) {
+				fmt.Fprint(w, "\033[49m ")
 			} else {
-				if y+1 < img.Bounds().Dy() && img.At(x, y+1) != color.Transparent {
+				if y+1 < img.Bounds().Dy() && !isFullyTransparent(img.At(x, y+1)) {
 					r, g, b, _ := img.At(x, y+1).RGBA()
 					fmt.Fprintf(w, "\033[48;2;%d;%d;%dm", r>>8, g>>8, b>>8)
 				} else {
@@ -241,11 +240,12 @@ func printImgSixel(w io.Writer, img image.PalettedImage) {
 			}
 		}
 		for x := 0; x < img.Bounds().Dx(); x++ {
-			if img.At(x, y) == color.Transparent {
+			c := img.ColorIndexAt(x, y)
+			if c == 0 {
 				fmt.Fprint(w, "?")
 			} else {
 				char := '?' + 1<<(y%6)
-				fmt.Fprintf(w, "#%d%c", img.ColorIndexAt(x, y)-1, char)
+				fmt.Fprintf(w, "#%d%c", c-1, char)
 			}
 		}
 	}
@@ -450,7 +450,8 @@ func thumbnailer(args []string) error {
 
 func main() {
 	flag.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage: thumbnailer [FILE]...\n")
+		fmt.Fprintf(os.Stderr, "Usage: thumbnailer [OPTION]... [FILE]...\n")
+		flag.PrintDefaults()
 	}
 	flag.Parse()
 
-- 
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