diff --git a/tools/tui/loop/api.go b/tools/tui/loop/api.go
index ce747e5bd..6fa0bb606 100644
--- a/tools/tui/loop/api.go
+++ b/tools/tui/loop/api.go
@@ -7,7 +7,6 @@ import (
 	"encoding/hex"
 	"fmt"
 	"os"
-	"runtime"
 	"strings"
 	"time"
 
@@ -309,32 +308,11 @@ func (self *Loop) DebugPrintln(args ...any) {
 	}
 }
 
-func format_stacktrace_on_panic(r any) (text string, err error) {
-	pcs := make([]uintptr, 512)
-	n := runtime.Callers(3, pcs)
-	lines := []string{}
-	frames := runtime.CallersFrames(pcs[:n])
-	err = fmt.Errorf("Panicked: %s", r)
-	lines = append(lines, fmt.Sprintf("\r\nPanicked with error: %s\r\nStacktrace (most recent call first):\r\n", r))
-	found_first_frame := false
-	for frame, more := frames.Next(); more; frame, more = frames.Next() {
-		if !found_first_frame {
-			if strings.HasPrefix(frame.Function, "runtime.") {
-				continue
-			}
-			found_first_frame = true
-		}
-		lines = append(lines, fmt.Sprintf("%s\r\n\t%s:%d\r\n", frame.Function, frame.File, frame.Line))
-	}
-	text = strings.Join(lines, "")
-	return strings.TrimSpace(text), err
-}
-
 func (self *Loop) Run() (err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			var text string
-			text, err = format_stacktrace_on_panic(r)
+			text, err = utils.Format_stacktrace_on_panic(r)
 			is_terminal := tty.IsTerminal(os.Stderr.Fd())
 			if is_terminal {
 				os.Stderr.WriteString("\x1b]\x1b\\\x1bc\x1b[H\x1b[2J") // reset terminal
@@ -600,7 +578,7 @@ type SizedText struct {
 
 func (self *Loop) RecoverFromPanicInGoRoutine() {
 	if r := recover(); r != nil {
-		text, err := format_stacktrace_on_panic(r)
+		text, err := utils.Format_stacktrace_on_panic(r)
 		err = fmt.Errorf("Panicked in non-main go routine\n%s\n%w", text, err)
 		// print to kitty stdout as multiple go routines might panic but only
 		// one panic is reported by the main loop panic_channel
diff --git a/tools/utils/images/utils.go b/tools/utils/images/utils.go
index 6ab2631ad..e25f83e53 100644
--- a/tools/utils/images/utils.go
+++ b/tools/utils/images/utils.go
@@ -23,6 +23,14 @@ func (self *Context) NumberOfThreads() int {
 	return int(self.num_of_threads.Load())
 }
 
+func (self *Context) EffectiveNumberOfThreads() int {
+	ans := int(self.num_of_threads.Load())
+	if ans <= 0 {
+		ans = max(1, runtime.NumCPU())
+	}
+	return ans
+}
+
 // parallel processes the data in separate goroutines.
 func (self *Context) Parallel(start, stop int, fn func(<-chan int)) {
 	count := stop - start
@@ -30,14 +38,7 @@ func (self *Context) Parallel(start, stop int, fn func(<-chan int)) {
 		return
 	}
 
-	procs := self.NumberOfThreads()
-	if procs <= 0 {
-		procs = runtime.NumCPU()
-	}
-	if procs > count {
-		procs = count
-	}
-
+	procs := min(self.EffectiveNumberOfThreads(), count)
 	c := make(chan int, count)
 	for i := start; i < stop; i++ {
 		c <- i
@@ -45,7 +46,7 @@ func (self *Context) Parallel(start, stop int, fn func(<-chan int)) {
 	close(c)
 
 	var wg sync.WaitGroup
-	for i := 0; i < procs; i++ {
+	for range procs {
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
diff --git a/tools/utils/misc.go b/tools/utils/misc.go
index 5f9ed25b8..12470f60f 100644
--- a/tools/utils/misc.go
+++ b/tools/utils/misc.go
@@ -11,6 +11,7 @@ import (
 	"runtime"
 	"slices"
 	"strconv"
+	"strings"
 
 	"golang.org/x/exp/constraints"
 )
@@ -64,6 +65,27 @@ func Filter[T any](s []T, f func(x T) bool) []T {
 	return ans
 }
 
+func Format_stacktrace_on_panic(r any) (text string, err error) {
+	pcs := make([]uintptr, 512)
+	n := runtime.Callers(3, pcs)
+	lines := []string{}
+	frames := runtime.CallersFrames(pcs[:n])
+	err = fmt.Errorf("Panicked: %s", r)
+	lines = append(lines, fmt.Sprintf("\r\nPanicked with error: %s\r\nStacktrace (most recent call first):\r\n", r))
+	found_first_frame := false
+	for frame, more := frames.Next(); more; frame, more = frames.Next() {
+		if !found_first_frame {
+			if strings.HasPrefix(frame.Function, "runtime.") {
+				continue
+			}
+			found_first_frame = true
+		}
+		lines = append(lines, fmt.Sprintf("%s\r\n\t%s:%d\r\n", frame.Function, frame.File, frame.Line))
+	}
+	text = strings.Join(lines, "")
+	return strings.TrimSpace(text), err
+}
+
 func Map[T any, O any](f func(x T) O, s []T) []O {
 	ans := make([]O, 0, len(s))
 	for _, x := range s {