Add NoUpscale option

README.md

@@ -70,6 +70,8 @@ Commands:
     	Image height (default "0")
     --fit
     	Best fit for required width and height (default "false")
+    --no-upscale
+    	Do not upscale images already smaller than the requested width/height (default "false")
     --dpi
     	Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300) (default "0")
     --format
@@ -126,6 +128,8 @@ Commands:
     	Image height (default "0")
     --fit
     	Best fit for required width and height (default "false")
+    --no-upscale
+    	Do not upscale images already smaller than the requested width/height (default "false")
     --dpi
     	Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300) (default "0")
     --format
@@ -156,6 +160,8 @@ Commands:
     	Image height (default "0")
     --fit
     	Best fit for required width and height (default "false")
+    --no-upscale
+    	Do not upscale images already smaller than the requested width/height (default "false")
     --dpi
     	Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300) (default "0")
     --filter

cbconvert.go

@@ -39,6 +39,8 @@ type Options struct {
 	Height int
 	// Best fit for required width and height
 	Fit bool
+	// Do not upscale images already smaller than the requested width/height
+	NoUpscale bool
 	// Document rendering resolution in DPI (PDF, EPUB, etc.); 0 uses the default
 	DPI int
 	// 0=NearestNeighbor, 1=Box, 2=Linear, 3=MitchellNetravali, 4=CatmullRom, 6=Gaussian, 7=Lanczos
@@ -180,6 +182,7 @@ func (o Options) Args() []string {
 	num("width", o.Width, def.Width)
 	num("height", o.Height, def.Height)
 	flag("fit", o.Fit)
+	flag("no-upscale", o.NoUpscale)
 	num("dpi", o.DPI, def.DPI)
 	str("format", o.Format, def.Format)
 	str("archive", o.Archive, def.Archive)
@@ -360,11 +363,7 @@ func (c *Converter) Cover(file File) error {
 	}
 
 	if c.Opts.Width > 0 || c.Opts.Height > 0 {
-		if c.Opts.Fit {
+		cover = c.resizeFit(cover)
-			cover = fit(cover, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
-		} else {
-			cover = resize(cover, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
-		}
 	}
 
 	ext := c.Opts.Format
@@ -409,11 +408,7 @@ func (c *Converter) Thumbnail(file File) error {
 	}
 
 	if c.Opts.Width > 0 || c.Opts.Height > 0 {
-		if c.Opts.Fit {
+		cover = c.resizeFit(cover)
-			cover = fit(cover, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
-		} else {
-			cover = resize(cover, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
-		}
 	} else {
 		cover = resize(cover, 256, 0, filters[c.Opts.Filter])
 	}

cbconvert_convert.go

@@ -326,11 +326,7 @@ func (c *Converter) imageTransform(img image.Image) image.Image {
 	var i = img
 
 	if c.Opts.Width > 0 || c.Opts.Height > 0 {
-		if c.Opts.Fit {
+		i = c.resizeFit(i)
-			i = fit(i, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
-		} else {
-			i = resize(i, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
-		}
 	}
 
 	if c.Opts.Rotate > 0 {

cbconvert_image.go

@@ -86,6 +86,26 @@ func fit(img image.Image, width, height int, filter transform.ResampleFilter) *i
 	return resize(img, dstW, dstH, filter)
 }
 
+// withinBounds reports whether img already fits within width by height; a zero dimension is unbounded.
+func withinBounds(img image.Image, width, height int) bool {
+	b := img.Bounds()
+
+	return (width == 0 || b.Dx() <= width) && (height == 0 || b.Dy() <= height)
+}
+
+// resizeFit resizes img to the configured width/height, honoring Fit and NoUpscale.
+func (c *Converter) resizeFit(img image.Image) image.Image {
+	if c.Opts.Fit {
+		return fit(img, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
+	}
+
+	if c.Opts.NoUpscale && withinBounds(img, c.Opts.Width, c.Opts.Height) {
+		return img
+	}
+
+	return resize(img, c.Opts.Width, c.Opts.Height, filters[c.Opts.Filter])
+}
+
 func rotate(img image.Image, angle float64) *image.RGBA {
 	return transform.Rotate(img, angle, &transform.RotationOptions{ResizeBounds: true, Pivot: &image.Point{}})
 }

cbconvert_test.go

@@ -114,17 +114,68 @@ func TestArgs(t *testing.T) {
 	opts.Effort = 4
 	opts.Lossless = true
 	opts.Width = 1200
+	opts.NoUpscale = true
 	opts.DPI = 150
 	opts.Grayscale = true
 	opts.OutDir = "/out"
 
 	got := strings.Join(opts.Args(), " ")
-	want := "--width 1200 --dpi 150 --format webp --quality 90 --effort 4 --lossless --grayscale --outdir /out"
+	want := "--width 1200 --no-upscale --dpi 150 --format webp --quality 90 --effort 4 --lossless --grayscale --outdir /out"
 	if got != want {
 		t.Errorf("Args() = %q, want %q", got, want)
 	}
 }
 
+func TestNoUpscale(t *testing.T) {
+	tmpDir, err := os.MkdirTemp(os.TempDir(), "cbc")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	width := func(o Options) int {
+		conv := New(o)
+		files, err := conv.Files([]string{"testdata/test.cbz"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, file := range files {
+			if err := conv.Convert(file); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		return firstPage(t, conv, filepath.Join(tmpDir, "test.cbz")).Bounds().Dx()
+	}
+
+	base := NewOptions()
+	base.OutDir = tmpDir
+	orig := width(base)
+
+	up := NewOptions()
+	up.OutDir = tmpDir
+	up.Width = orig * 2
+	up.NoUpscale = true
+	if got := width(up); got != orig {
+		t.Errorf("NoUpscale should keep original width %d, got %d", orig, got)
+	}
+
+	no := NewOptions()
+	no.OutDir = tmpDir
+	no.Width = orig * 2
+	if got := width(no); got != orig*2 {
+		t.Errorf("without NoUpscale should upscale to %d, got %d", orig*2, got)
+	}
+
+	down := NewOptions()
+	down.OutDir = tmpDir
+	down.Width = orig / 2
+	down.NoUpscale = true
+	if got := width(down); got != orig/2 {
+		t.Errorf("NoUpscale should still downscale to %d, got %d", orig/2, got)
+	}
+}
+
 func TestConvertDPI(t *testing.T) {
 	tmpDir, err := os.MkdirTemp(os.TempDir(), "cbc")
 	if err != nil {

cmd/cbconvert-gui/options.go

@@ -25,6 +25,7 @@ func options() cbconvert.Options {
 	opts.Height = iup.GetHandle("Height").GetInt("VALUE")
 	opts.DPI = dpiValue(iup.GetHandle("DPI").GetAttribute("VALUE"))
 	opts.Fit = iup.GetHandle("Fit").GetAttribute("VALUE") == "ON"
+	opts.NoUpscale = iup.GetHandle("NoUpscale").GetAttribute("VALUE") == "ON"
 	opts.Filter = iup.GetHandle("Filter").GetInt("VALUE") - 1
 	opts.Quality = iup.GetHandle("Quality").GetInt("VALUE")
 	switch opts.Format {

cmd/cbconvert-gui/settings.go

@@ -39,6 +39,7 @@ var settings = []setting{
 	{"NoNonImage", kindBool, "OFF"},
 	{"Combine", kindBool, "OFF"},
 	{"Fit", kindBool, "OFF"},
+	{"NoUpscale", kindBool, "OFF"},
 	{"Lossless", kindBool, "OFF"},
 	{"Grayscale", kindBool, "OFF"},
 	{"OutDir", kindStr, ""},

cmd/cbconvert-gui/widgets.go

@@ -359,6 +359,8 @@ func tabImage() iup.Ihandle {
 			iup.Vbox(
 				iup.Toggle(" Best Fit").SetHandle("Fit").
 					SetAttributes(`TIP="Best fit for required width and height"`),
+				iup.Toggle(" No Upscale").SetHandle("NoUpscale").
+					SetAttribute("TIP", "Do not enlarge images already smaller than the requested size"),
 			),
 			iup.Vbox(
 				iup.Label("Resize Filter:"),

cmd/cbconvert/go.mod

@@ -5,6 +5,7 @@ go 1.26
 require (
 	github.com/gen2brain/cbconvert v1.0.5-0.20260623161611-a5817c3ba5de
 	github.com/schollz/progressbar/v3 v3.19.0
+	golang.org/x/term v0.44.0
 )
 
 require (
@@ -52,7 +53,6 @@ require (
 	golang.org/x/net v0.56.0 // indirect
 	golang.org/x/sync v0.21.0 // indirect
 	golang.org/x/sys v0.46.0 // indirect
-	golang.org/x/term v0.44.0 // indirect
 	golang.org/x/text v0.38.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )

cmd/cbconvert/main.go

@@ -192,6 +192,7 @@ func parseFlags() (cbconvert.Options, []string) {
 	convert.IntVar(&opts.Width, "width", 0, "Image width")
 	convert.IntVar(&opts.Height, "height", 0, "Image height")
 	convert.BoolVar(&opts.Fit, "fit", false, "Best fit for required width and height")
+	convert.BoolVar(&opts.NoUpscale, "no-upscale", false, "Do not upscale images already smaller than the requested width/height")
 	convert.IntVar(&opts.DPI, "dpi", 0, "Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300)")
 	convert.StringVar(&opts.Format, "format", "jpeg", "Image format, valid values are jpeg, png, tiff, bmp, webp, avif, jxl")
 	convert.StringVar(&opts.Archive, "archive", "zip", "Archive format, valid values are zip, tar")
@@ -220,6 +221,7 @@ func parseFlags() (cbconvert.Options, []string) {
 	cover.IntVar(&opts.Width, "width", 0, "Image width")
 	cover.IntVar(&opts.Height, "height", 0, "Image height")
 	cover.BoolVar(&opts.Fit, "fit", false, "Best fit for required width and height")
+	cover.BoolVar(&opts.NoUpscale, "no-upscale", false, "Do not upscale images already smaller than the requested width/height")
 	cover.IntVar(&opts.DPI, "dpi", 0, "Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300)")
 	cover.StringVar(&opts.Format, "format", "jpeg", "Image format, valid values are jpeg, png, tiff, bmp, webp, avif")
 	cover.IntVar(&opts.Quality, "quality", 75, "Image quality")
@@ -235,6 +237,7 @@ func parseFlags() (cbconvert.Options, []string) {
 	thumbnail.IntVar(&opts.Width, "width", 0, "Image width")
 	thumbnail.IntVar(&opts.Height, "height", 0, "Image height")
 	thumbnail.BoolVar(&opts.Fit, "fit", false, "Best fit for required width and height")
+	thumbnail.BoolVar(&opts.NoUpscale, "no-upscale", false, "Do not upscale images already smaller than the requested width/height")
 	thumbnail.IntVar(&opts.DPI, "dpi", 0, "Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300)")
 	thumbnail.IntVar(&opts.Filter, "filter", 2, "0=NearestNeighbor, 1=Box, 2=Linear, 3=MitchellNetravali, 4=CatmullRom, 6=Gaussian, 7=Lanczos")
 	thumbnail.StringVar(&opts.OutDir, "outdir", ".", "Output directory")
@@ -256,7 +259,7 @@ func parseFlags() (cbconvert.Options, []string) {
 		fmt.Fprintf(os.Stderr, "Usage: %s <command> [<flags>] [file1 dir1 ... fileOrDirN]\n\n", filepath.Base(os.Args[0]))
 		fmt.Fprintf(os.Stderr, "\nCommands:\n")
 		fmt.Fprintf(os.Stderr, "\n  convert\n    \tConvert archive or document\n\n")
-		order := []string{"width", "height", "fit", "dpi", "format", "archive", "zip-level", "quality", "effort", "lossless", "combine", "outfile", "filter", "no-cover", "no-rgb",
+		order := []string{"width", "height", "fit", "no-upscale", "dpi", "format", "archive", "zip-level", "quality", "effort", "lossless", "combine", "outfile", "filter", "no-cover", "no-rgb",
 			"no-nonimage", "no-convert", "grayscale", "rotate", "brightness", "contrast", "suffix", "outdir", "size", "recursive", "quiet"}
 		for _, name := range order {
 			f := convert.Lookup(name)
@@ -264,14 +267,14 @@ func parseFlags() (cbconvert.Options, []string) {
 			fmt.Fprintf(os.Stderr, "%v (default %q)\n", f.Usage, f.DefValue)
 		}
 		fmt.Fprintf(os.Stderr, "\n  cover\n    \tExtract cover\n\n")
-		order = []string{"width", "height", "fit", "dpi", "format", "quality", "effort", "lossless", "filter", "outdir", "size", "recursive", "quiet"}
+		order = []string{"width", "height", "fit", "no-upscale", "dpi", "format", "quality", "effort", "lossless", "filter", "outdir", "size", "recursive", "quiet"}
 		for _, name := range order {
 			f := cover.Lookup(name)
 			fmt.Fprintf(os.Stderr, "    --%s\n    \t", f.Name)
 			fmt.Fprintf(os.Stderr, "%v (default %q)\n", f.Usage, f.DefValue)
 		}
 		fmt.Fprintf(os.Stderr, "\n  thumbnail\n    \tExtract cover thumbnail (freedesktop spec.)\n\n")
-		order = []string{"width", "height", "fit", "dpi", "filter", "outdir", "outfile", "size", "recursive", "quiet"}
+		order = []string{"width", "height", "fit", "no-upscale", "dpi", "filter", "outdir", "outfile", "size", "recursive", "quiet"}
 		for _, name := range order {
 			f := thumbnail.Lookup(name)
 			fmt.Fprintf(os.Stderr, "    --%s\n    \t", f.Name)