diff --git a/BACKLOG.md b/BACKLOG.md
index e919e5c3..67aaf0ad 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -4,17 +4,18 @@
 
 
 **🚨 CRITICAL: CI test suite failures - user-visible rendering broken**
+- [ ] #401: Fix - CI test-coverage failing with segfaults in colored_contours and ascii_heatmap_demo (blocks all PR merges)
 
 **🚨 CRITICAL: User-visible PNG/PDF rendering regressions**
 
 **User-Facing Issues (Medium Priority)**
-- [ ] #377: Enhancement - make finer grid on pcolormesh_demo.html (enhancement)
+*All user-facing issues moved to DOING*
 
 **Infrastructure & Documentation Issues (Lower Priority)**
 - [ ] #388: Fix - investigate test_mpeg_consolidated failure unrelated to ylabel rotation (test infrastructure)
 
 ## DOING (Current Work)
-*No current work - ready for next task*
+- [x] #377: Enhancement - make finer grid on pcolormesh_demo.html (branch: enhance-finer-grid-377)
 
 ## FUTURE SPRINTS - Systematic Restoration
 
diff --git a/example/fortran/pcolormesh_demo/pcolormesh_demo.f90 b/example/fortran/pcolormesh_demo/pcolormesh_demo.f90
index 8f5be758..5a4a9bc1 100644
--- a/example/fortran/pcolormesh_demo/pcolormesh_demo.f90
+++ b/example/fortran/pcolormesh_demo/pcolormesh_demo.f90
@@ -12,29 +12,33 @@ program pcolormesh_demo
 contains
 
     subroutine demo_basic_gradient()
-        !! Basic pcolormesh with simple gradient
-        real(wp) :: x(6), y(5)
-        real(wp) :: c(4, 5)
+        !! Basic pcolormesh with simple gradient - enhanced 51x51 grid
+        real(wp) :: x(51), y(51)
+        real(wp) :: c(50, 50)
         integer :: i, j
+        real(wp) :: dx, dy
         
-        ! Create coordinate arrays for regular grid
-        do i = 1, 6
-            x(i) = real(i-1, wp) * 0.4_wp
+        ! Create coordinate arrays for high-resolution regular grid
+        dx = 2.0_wp / 50.0_wp  ! Total range 2.0, 50 intervals
+        dy = 1.2_wp / 50.0_wp  ! Total range 1.2, 50 intervals
+        
+        do i = 1, 51
+            x(i) = real(i-1, wp) * dx
         end do
-        do i = 1, 5
-            y(i) = real(i-1, wp) * 0.3_wp
+        do i = 1, 51
+            y(i) = real(i-1, wp) * dy
         end do
         
-        ! Create test data - simple gradient
-        do i = 1, 4
-            do j = 1, 5
-                c(i, j) = real(i, wp) + real(j, wp) * 0.5_wp
+        ! Create test data - smooth gradient across high-res grid
+        do i = 1, 50
+            do j = 1, 50
+                c(i, j) = real(i, wp) / 50.0_wp + real(j, wp) / 50.0_wp * 0.5_wp
             end do
         end do
         
         ! Create pcolormesh plot
         call figure(figsize=[6.4_wp, 4.8_wp])
-        call title('Basic Pcolormesh - Linear Gradient')
+        call title('Basic Pcolormesh - Linear Gradient (50x50 resolution)')
         call xlabel('X coordinate')
         call ylabel('Y coordinate')
         call pcolormesh(x, y, c, colormap='viridis')
@@ -45,32 +49,36 @@ subroutine demo_basic_gradient()
     end subroutine demo_basic_gradient
 
     subroutine demo_sinusoidal_pattern()
-        !! Pcolormesh with sinusoidal pattern
-        real(wp) :: x(9), y(9)
-        real(wp) :: c(8, 8)
+        !! Pcolormesh with sinusoidal pattern - enhanced 51x51 grid
+        real(wp) :: x(51), y(51)
+        real(wp) :: c(50, 50)
         real(wp) :: xi, yj
         integer :: i, j
         real(wp), parameter :: pi = 3.14159265359_wp
+        real(wp) :: dx, dy
+        
+        ! Create coordinate arrays for high-resolution grid
+        dx = 1.6_wp / 50.0_wp  ! Total range 1.6, 50 intervals
+        dy = 1.2_wp / 50.0_wp  ! Total range 1.2, 50 intervals
         
-        ! Create coordinate arrays
-        do i = 1, 9
-            x(i) = real(i-1, wp) * 0.2_wp
+        do i = 1, 51
+            x(i) = real(i-1, wp) * dx
         end do
-        do i = 1, 9
-            y(i) = real(i-1, wp) * 0.15_wp
+        do i = 1, 51
+            y(i) = real(i-1, wp) * dy
         end do
         
-        ! Create sinusoidal pattern  
-        do i = 1, 8
-            do j = 1, 8
-                xi = (x(i) + x(i+1)) * 0.5_wp  ! Center of quad
-                yj = (y(j) + y(j+1)) * 0.5_wp  ! Center of quad 
+        ! Create sinusoidal pattern with proper sampling
+        do i = 1, 50
+            do j = 1, 50
+                xi = (x(i) + x(i+1)) * 0.5_wp  ! Center of cell
+                yj = (y(j) + y(j+1)) * 0.5_wp  ! Center of cell
                 c(i, j) = sin(2.0_wp * pi * xi) * cos(3.0_wp * pi * yj)
             end do
         end do
         
         call figure(figsize=[6.4_wp, 4.8_wp])
-        call title('Pcolormesh - Sinusoidal Pattern')
+        call title('Pcolormesh - Sinusoidal Pattern (50x50 resolution)')
         call xlabel('X coordinate')
         call ylabel('Y coordinate')
         call pcolormesh(x, y, c, colormap='coolwarm')
@@ -81,31 +89,37 @@ subroutine demo_sinusoidal_pattern()
     end subroutine demo_sinusoidal_pattern
 
     subroutine demo_different_colormaps()
-        !! Demo different colormaps
-        real(wp) :: x(6), y(6)
-        real(wp) :: c(5, 5)
-        real(wp) :: r
+        !! Demo different colormaps - enhanced 51x51 grid
+        real(wp) :: x(51), y(51)
+        real(wp) :: c(50, 50)
+        real(wp) :: r, xi, yj
         integer :: i, j
         real(wp), parameter :: pi = 3.14159265359_wp
+        real(wp) :: dx, dy
+        
+        ! Create coordinate arrays for high-resolution grid
+        dx = 1.5_wp / 50.0_wp  ! Total range 1.5, 50 intervals
+        dy = 1.25_wp / 50.0_wp ! Total range 1.25, 50 intervals
         
-        ! Create coordinate arrays
-        do i = 1, 6
-            x(i) = real(i-1, wp) * 0.3_wp
+        do i = 1, 51
+            x(i) = real(i-1, wp) * dx
         end do
-        do i = 1, 6
-            y(i) = real(i-1, wp) * 0.25_wp
+        do i = 1, 51
+            y(i) = real(i-1, wp) * dy
         end do
         
-        ! Create radial pattern
-        do i = 1, 5
-            do j = 1, 5
-                r = sqrt((x(i) - 1.0_wp)**2 + (y(j) - 0.6_wp)**2)
+        ! Create radial pattern with proper sampling
+        do i = 1, 50
+            do j = 1, 50
+                xi = (x(i) + x(i+1)) * 0.5_wp  ! Center of cell
+                yj = (y(j) + y(j+1)) * 0.5_wp  ! Center of cell
+                r = sqrt((xi - 0.75_wp)**2 + (yj - 0.625_wp)**2)
                 c(i, j) = exp(-r)
             end do
         end do
         
         call figure(figsize=[6.4_wp, 4.8_wp])
-        call title('Pcolormesh - Radial Pattern (Plasma)')
+        call title('Pcolormesh - Radial Pattern (Plasma) (50x50 resolution)')
         call xlabel('X coordinate')
         call ylabel('Y coordinate')
         call pcolormesh(x, y, c, colormap='plasma')
diff --git a/src/fortplot_matplotlib.f90 b/src/fortplot_matplotlib.f90
index 4a1596c9..0e81d64b 100644
--- a/src/fortplot_matplotlib.f90
+++ b/src/fortplot_matplotlib.f90
@@ -156,13 +156,22 @@ subroutine pcolormesh(x, y, z, shading, colormap, show_colorbar, label, &
             wp_linewidths = real(linewidths, wp)
         end if
         
-        ! Forward SUPPORTED parameters to underlying method using single call pattern
-        call fig%add_pcolormesh(wp_x, wp_y, wp_z, &
-            colormap=merge(colormap, "", present(colormap)), &
-            vmin=merge(wp_vmin, 0.0_wp, present(vmin)), &
-            vmax=merge(wp_vmax, 0.0_wp, present(vmax)), &
-            edgecolors=merge(wp_edgecolors, [0.0_wp, 0.0_wp, 0.0_wp], present(edgecolors)), &
-            linewidths=merge(wp_linewidths, 0.0_wp, present(linewidths)))
+        ! Forward SUPPORTED parameters to underlying method using conditional calls
+        if (present(colormap) .and. present(vmin) .and. present(vmax) .and. &
+            present(edgecolors) .and. present(linewidths)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, &
+                colormap=colormap, vmin=wp_vmin, vmax=wp_vmax, &
+                edgecolors=wp_edgecolors, linewidths=wp_linewidths)
+        else if (present(colormap) .and. present(vmin) .and. present(vmax)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, &
+                colormap=colormap, vmin=wp_vmin, vmax=wp_vmax)
+        else if (present(colormap)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, colormap=colormap)
+        else if (present(vmin) .and. present(vmax)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, vmin=wp_vmin, vmax=wp_vmax)
+        else
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z)
+        end if
         
         deallocate(wp_x, wp_y, wp_z)
     end subroutine pcolormesh
@@ -472,13 +481,22 @@ subroutine add_pcolormesh(x, y, z, shading, colormap, show_colorbar, label, &
             wp_linewidths = real(linewidths, wp)
         end if
         
-        ! Forward SUPPORTED parameters to underlying method using single call pattern
-        call fig%add_pcolormesh(wp_x, wp_y, wp_z, &
-            colormap=merge(colormap, "", present(colormap)), &
-            vmin=merge(wp_vmin, 0.0_wp, present(vmin)), &
-            vmax=merge(wp_vmax, 0.0_wp, present(vmax)), &
-            edgecolors=merge(wp_edgecolors, [0.0_wp, 0.0_wp, 0.0_wp], present(edgecolors)), &
-            linewidths=merge(wp_linewidths, 0.0_wp, present(linewidths)))
+        ! Forward SUPPORTED parameters to underlying method using conditional calls
+        if (present(colormap) .and. present(vmin) .and. present(vmax) .and. &
+            present(edgecolors) .and. present(linewidths)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, &
+                colormap=colormap, vmin=wp_vmin, vmax=wp_vmax, &
+                edgecolors=wp_edgecolors, linewidths=wp_linewidths)
+        else if (present(colormap) .and. present(vmin) .and. present(vmax)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, &
+                colormap=colormap, vmin=wp_vmin, vmax=wp_vmax)
+        else if (present(colormap)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, colormap=colormap)
+        else if (present(vmin) .and. present(vmax)) then
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z, vmin=wp_vmin, vmax=wp_vmax)
+        else
+            call fig%add_pcolormesh(wp_x, wp_y, wp_z)
+        end if
         
         deallocate(wp_x, wp_y, wp_z)
     end subroutine add_pcolormesh
diff --git a/test/test_pcolormesh_enhanced_resolution.f90 b/test/test_pcolormesh_enhanced_resolution.f90
new file mode 100644
index 00000000..a61de012
--- /dev/null
+++ b/test/test_pcolormesh_enhanced_resolution.f90
@@ -0,0 +1,174 @@
+program test_pcolormesh_enhanced_resolution
+    !! Test enhanced grid resolution for pcolormesh demo
+    !! Verifies that enhanced grids maintain pattern fidelity at higher resolution
+    
+    use iso_fortran_env, only: wp => real64
+    use fortplot
+    implicit none
+    
+    logical :: test_passed
+    character(len=256) :: error_msg
+    
+    test_passed = .true.
+    error_msg = ""
+    
+    print *, "Testing enhanced resolution pcolormesh grids..."
+    
+    ! Test enhanced basic gradient  
+    call test_enhanced_basic_gradient()
+    
+    ! Test enhanced sinusoidal pattern
+    call test_enhanced_sinusoidal_pattern()
+    
+    ! Test enhanced radial pattern
+    call test_enhanced_radial_pattern()
+    
+    if (test_passed) then
+        print *, "PASS: All enhanced resolution tests passed"
+        stop 0
+    else
+        print *, "FAIL: ", trim(error_msg)
+        stop 1
+    end if
+    
+contains
+
+    subroutine test_enhanced_basic_gradient()
+        !! Test enhanced basic gradient with 51x51 grid (50x50 cells)
+        real(wp) :: x(51), y(51), c(50, 50)
+        integer :: i, j, file_size
+        real(wp) :: dx, dy
+        
+        print *, "Testing enhanced basic gradient (50x50 cells)..."
+        
+        ! Create coordinate arrays for high-resolution grid
+        dx = 2.0_wp / 50.0_wp  ! Total range 2.0, 50 intervals
+        dy = 1.2_wp / 50.0_wp  ! Total range 1.2, 50 intervals
+        
+        do i = 1, 51
+            x(i) = real(i-1, wp) * dx
+        end do
+        do i = 1, 51
+            y(i) = real(i-1, wp) * dy
+        end do
+        
+        ! Create test data - smooth gradient across high-res grid
+        do i = 1, 50
+            do j = 1, 50
+                c(i, j) = real(i, wp) / 50.0_wp + real(j, wp) / 50.0_wp * 0.5_wp
+            end do
+        end do
+        
+        ! Create pcolormesh plot
+        call figure(figsize=[6.4_wp, 4.8_wp])
+        call title('Enhanced Basic Gradient (50x50)')
+        call xlabel('X coordinate')
+        call ylabel('Y coordinate')
+        call pcolormesh(x, y, c, colormap='viridis')
+        call savefig('test_enhanced_basic_gradient.png')
+        
+        ! Verify file was created and has reasonable size
+        file_size = get_file_size('test_enhanced_basic_gradient.png')
+        if (file_size < 1000) then
+            test_passed = .false.
+            error_msg = "Enhanced basic gradient PNG too small or not created"
+        end if
+    end subroutine test_enhanced_basic_gradient
+    
+    subroutine test_enhanced_sinusoidal_pattern()
+        !! Test enhanced sinusoidal pattern with 51x51 grid (50x50 cells)
+        real(wp) :: x(51), y(51), c(50, 50)
+        real(wp) :: xi, yj, dx, dy
+        integer :: i, j, file_size
+        real(wp), parameter :: pi = 3.14159265359_wp
+        
+        print *, "Testing enhanced sinusoidal pattern (50x50 cells)..."
+        
+        ! Create coordinate arrays for high-resolution grid
+        dx = 1.6_wp / 50.0_wp  ! Total range 1.6, 50 intervals
+        dy = 1.2_wp / 50.0_wp  ! Total range 1.2, 50 intervals
+        
+        do i = 1, 51
+            x(i) = real(i-1, wp) * dx
+        end do
+        do i = 1, 51
+            y(i) = real(i-1, wp) * dy
+        end do
+        
+        ! Create sinusoidal pattern with proper sampling
+        do i = 1, 50
+            do j = 1, 50
+                xi = (x(i) + x(i+1)) * 0.5_wp  ! Center of cell
+                yj = (y(j) + y(j+1)) * 0.5_wp  ! Center of cell
+                c(i, j) = sin(2.0_wp * pi * xi) * cos(3.0_wp * pi * yj)
+            end do
+        end do
+        
+        call figure(figsize=[6.4_wp, 4.8_wp])
+        call title('Enhanced Sinusoidal Pattern (50x50)')
+        call xlabel('X coordinate')
+        call ylabel('Y coordinate')
+        call pcolormesh(x, y, c, colormap='coolwarm')
+        call savefig('test_enhanced_sinusoidal_pattern.png')
+        
+        ! Verify file was created and has reasonable size
+        file_size = get_file_size('test_enhanced_sinusoidal_pattern.png')
+        if (file_size < 1000) then
+            test_passed = .false.
+            error_msg = "Enhanced sinusoidal pattern PNG too small or not created"
+        end if
+    end subroutine test_enhanced_sinusoidal_pattern
+    
+    subroutine test_enhanced_radial_pattern()
+        !! Test enhanced radial pattern with 51x51 grid (50x50 cells)
+        real(wp) :: x(51), y(51), c(50, 50)
+        real(wp) :: r, dx, dy, xi, yj
+        integer :: i, j, file_size
+        
+        print *, "Testing enhanced radial pattern (50x50 cells)..."
+        
+        ! Create coordinate arrays for high-resolution grid
+        dx = 1.5_wp / 50.0_wp  ! Total range 1.5, 50 intervals
+        dy = 1.25_wp / 50.0_wp  ! Total range 1.25, 50 intervals
+        
+        do i = 1, 51
+            x(i) = real(i-1, wp) * dx
+        end do
+        do i = 1, 51
+            y(i) = real(i-1, wp) * dy
+        end do
+        
+        ! Create radial pattern with proper sampling
+        do i = 1, 50
+            do j = 1, 50
+                xi = (x(i) + x(i+1)) * 0.5_wp  ! Center of cell
+                yj = (y(j) + y(j+1)) * 0.5_wp  ! Center of cell
+                r = sqrt((xi - 0.75_wp)**2 + (yj - 0.625_wp)**2)
+                c(i, j) = exp(-r)
+            end do
+        end do
+        
+        call figure(figsize=[6.4_wp, 4.8_wp])
+        call title('Enhanced Radial Pattern (50x50)')
+        call xlabel('X coordinate')
+        call ylabel('Y coordinate')
+        call pcolormesh(x, y, c, colormap='plasma')
+        call savefig('test_enhanced_radial_pattern.png')
+        
+        ! Verify file was created and has reasonable size
+        file_size = get_file_size('test_enhanced_radial_pattern.png')
+        if (file_size < 1000) then
+            test_passed = .false.
+            error_msg = "Enhanced radial pattern PNG too small or not created"
+        end if
+    end subroutine test_enhanced_radial_pattern
+    
+    integer function get_file_size(filename)
+        character(len=*), intent(in) :: filename
+        integer(8) :: size
+        
+        inquire(file=filename, size=size)
+        get_file_size = int(size)
+    end function get_file_size
+
+end program test_pcolormesh_enhanced_resolution
\ No newline at end of file