diff --git a/src/gui.jl b/src/gui.jl
index 1acefee..bca9e43 100644
--- a/src/gui.jl
+++ b/src/gui.jl
@@ -30,8 +30,12 @@ function gui(
         crop_bottom::Int = 0,
         crop_left::Int = 0,
         crop_right::Int = 0,
+        min_size = 100,                     # minimum size of segments to keep
         colorproj = RGB{Float32}(1, 1, -2), # used for identifying the stimulus
+        expectedpixels = 40000,             # ""
         expectedloc = nothing,              # ""
+        max_size_frac = 0.1,                # sets largest allowed spot size
+        min_size_pixels = 10                # sets smallest allowed spot size
     )
     channelpct(x) = string(round(Int, x * 100)) * '%'
 
@@ -122,7 +126,7 @@ function gui(
     update_threshold = change -> begin
         newvalue = round(threshold + change; digits=2)
         try
-            seg = segment_image(rescaledimg; threshold = newvalue)
+            seg = segment_image(rescaledimg; threshold = newvalue, min_size = min_size)
             nsegs = length(segment_labels(seg))
             nsegs > length(colors) && @warn "More than $(length(colors)) segments ($(nsegs)). Excluded ones will be displayed in white and will not be selectable"
             empty!(labels2idx)
@@ -134,7 +138,7 @@ function gui(
                 push!(idx2labels, idx=>l)
             end
             centroidsacc, _ = get_centroidsacc(seg.image_indexmap)
-            istim = labels2idx[stimulus_index(seg, centroidsacc; colorproj = colorproj, expectedloc = expectedloc)]            
+            istim = labels2idx[stimulus_index(seg, centroidsacc; colorproj = colorproj, expectedpixels = expectedpixels, expectedloc = expectedloc)]            
             for (j, cb) in enumerate(cbs)
                 # set_gtk_property!(cb, "active", j <= nsegs)
                 cb[] = (j == istim || j == preclick)
@@ -182,7 +186,7 @@ function gui(
         img = color.(load(file))[crop_top+1:end-crop_bottom, crop_left+1:end-crop_right]
         rescaledimg = isnothing(bkgimg) ? img : (img ./ bkgimg .* bkgmean)
 
-        seg = segment_image(rescaledimg; threshold = threshold)
+        seg = segment_image(rescaledimg; threshold = threshold, min_size = min_size)
         nsegs = length(segment_labels(seg))
         nsegs > length(colors) && @warn "More than $(length(colors)) segments ($(nsegs)). Excluded ones will be displayed in white and will not be selectable"
         empty!(labels2idx)
@@ -194,7 +198,7 @@ function gui(
             push!(idx2labels, idx=>l)
         end
         centroidsacc, _ = get_centroidsacc(seg.image_indexmap)
-        istim = labels2idx[stimulus_index(seg, centroidsacc; colorproj = colorproj, expectedloc = expectedloc)]            
+        istim = labels2idx[stimulus_index(seg, centroidsacc; colorproj = colorproj, expectedpixels = expectedpixels, expectedloc = expectedloc)]            
         for (j, cb) in enumerate(cbs)
             # set_gtk_property!(cb, "active", j <= nsegs)
             cb[] = (j == istim || j == preclick)
@@ -214,7 +218,7 @@ function gui(
         pixelskeep = map(i -> i ∈ keep, labels_map(seg))
         L = label_components(pixelskeep)
         newseg = SegmentedImage(img, L)
-        spotdict, stimulus = spots(newseg; colorproj = colorproj, expectedloc = expectedloc)
+        spotdict, stimulus = spots(newseg; colorproj = colorproj, expectedpixels = expectedpixels, expectedloc = expectedloc, max_size_frac = max_size_frac, min_size_pixels = min_size_pixels)
         push!(results, (file, spotdict, stimulus, newseg))
     end
 
diff --git a/src/segment.jl b/src/segment.jl
index 192e740..347fd92 100644
--- a/src/segment.jl
+++ b/src/segment.jl
@@ -10,7 +10,7 @@ function segment_image(
         img::AbstractMatrix{<:Color};
         threshold::Real = 0.2,      # threshold for color similarity in region growing
         prune::Bool = true,         # prune small segments
-        min_size::Int = 500,        # minimum size of segments to keep
+        min_size::Int = 100,        # minimum size of segments to keep
     )
     seg = unseeded_region_growing(img, threshold)
     if prune
@@ -22,27 +22,27 @@ end
 segment_image(img::AbstractMatrix{<:Colorant}; kwargs...) = segment_image(color.(img); kwargs...)
 
 """
-    idx = stimulus_index(seg::SegmentedImage, centroidsacc; colorproj = RGB(1, 1, -2), expectedloc = nothing)
+    idx = stimulus_index(seg::SegmentedImage, centroidsacc; colorproj = RGB(1, 1, -2), expectedpixels = 50000, expectedloc = nothing)
 
 Given a segmented image `seg`, return the index of the segment that scores
-highest on the product of (1) projection (dot product) with `colorproj` and (2)
-number of pixels.
+highest on the quotient of (1) projection (dot product) with `colorproj` with (2)
+the absolute value of the difference between the number of pixels with `expectedpixels`.
 
 Optionally, if images were taken with a fixed location for the stimulus, a segment's score
 is divided by the squared distance of its centroid (via `centroidsacc`) from the position given by `expectedloc`.
 """
-function stimulus_index(seg::SegmentedImage, centroidsacc; colorproj = RGB{Float32}(1, 1, -2), expectedloc = nothing)
+function stimulus_index(seg::SegmentedImage, centroidsacc; colorproj = RGB{Float32}(1, 1, -2), expectedpixels = 40000, expectedloc = nothing)
     if !isnothing(expectedloc)
         proj = map(segment_labels(seg)) do l
             l == 0 && return 0
             val = centroidsacc[l]
             centroid = [round(Int, val[1] / val[3]), round(Int, val[2] / val[3])]
-            return l => (colorproj ⋅ segment_mean(seg, l) * segment_pixel_count(seg, l) / max(1, sum(abs2, centroid .- expectedloc)))
+            return l => (colorproj ⋅ segment_mean(seg, l) / max(1, abs(segment_pixel_count(seg, l) - expectedpixels)) / max(1, sum(abs2, centroid .- expectedloc)))
         end
         (i, _) = argmax(last, proj)
         return i
     else 
-        proj = [l => (colorproj ⋅ segment_mean(seg, l)) * segment_pixel_count(seg, l) for l in segment_labels(seg)]
+        proj = [l => (colorproj ⋅ segment_mean(seg, l)) / max(1, abs(segment_pixel_count(seg, l) - expectedpixels)) for l in segment_labels(seg)]
         (i, _) = argmax(last, proj)
         return i
     end
@@ -110,18 +110,18 @@ Spots larger than `max_size_frac * npixels` (default: 10% of the image) are igno
 function spots(
         seg::SegmentedImage;
         max_size_frac=0.1,            # no spot is bigger than max_size_frac * npixels
+        min_size_pixels=10,           # smallest allowed spot
         kwargs...
     )
     centroidsacc, nadj = get_centroidsacc(seg.image_indexmap)
     istim = stimulus_index(seg, centroidsacc; kwargs...)
-
     stimulus = Ref{Pair{Int,Spot}}()
     filter!(centroidsacc) do (key, val)
         if key == istim
             stimulus[] = key => Spot(val[3], (round(Int, val[1] / val[3]), round(Int, val[2] / val[3])))
             return false
         end
-        return val[3] <= max_size_frac * length(seg.image_indexmap)
+        return min_size_pixels <= val[3] <= max_size_frac * length(seg.image_indexmap)
         # # is the centroid within the segment?
         # x, y = round(Int, val[1] / val[3]), round(Int, val[2] / val[3])
         # l = seg.image_indexmap[x, y]
@@ -148,6 +148,7 @@ function spots(
         indexmap::Matrix{Int},
         istim::Int;
         max_size_frac=0.1, 
+        min_size_pixels=10,
         kwargs...
     )
     centroidsacc, nadj = get_centroidsacc(indexmap)
@@ -157,7 +158,7 @@ function spots(
             stimulus[] = key => Spot(val[3], (round(Int, val[1] / val[3]), round(Int, val[2] / val[3])))
             return false
         end
-        return val[3] <= max_size_frac * length(indexmap)
+        return min_size_pixels <= val[3] <= max_size_frac * length(indexmap)
     end
     return Dict(l => Spot(val[3], (round(Int, val[1] / val[3]), round(Int, val[2] / val[3]))) for (l, val) in centroidsacc), stimulus[]
 end