use ratio 1.5 for perfect both side rendering

internal/converter/profiles/core.go

@@ -12,6 +12,19 @@ type Profile struct {
 	Height      int
 }
 
+const perfectRatio = 1.5
+
+func (p Profile) PerfectDim() (int, int) {
+	width, height := float64(p.Width), float64(p.Height)
+	perfectWidth, perfectHeight := height/perfectRatio, width*perfectRatio
+	if perfectWidth > width {
+		perfectWidth = width
+	} else {
+		perfectHeight = height
+	}
+	return int(perfectWidth), int(perfectHeight)
+}
+
 type Profiles []Profile
 
 func New() Profiles {

main.go

@@ -91,6 +91,8 @@ $ go install github.com/celogeek/go-comic-converter/v%d@%s
 	fmt.Fprintln(os.Stderr, cmd.Options)
 
 	profile := cmd.Options.GetProfile()
+	perfectWidth, perfectHeight := profile.PerfectDim()
+
 	if err := epub.NewEpub(&epub.EpubOptions{
 		Input:                      cmd.Options.Input,
 		Output:                     cmd.Options.Output,
@@ -102,8 +104,8 @@ $ go install github.com/celogeek/go-comic-converter/v%d@%s
 		DryVerbose:                 cmd.Options.DryVerbose,
 		SortPathMode:               cmd.Options.SortPathMode,
 		ImageOptions: &epub.ImageOptions{
-			ViewWidth:           profile.Width,
-			ViewHeight:          profile.Height,
+			ViewWidth:           perfectWidth,
+			ViewHeight:          perfectHeight,
 			Quality:             cmd.Options.Quality,
 			Crop:                cmd.Options.Crop,
 			Brightness:          cmd.Options.Brightness,