Get channel histogram bounds at once and then filter (instead of the …

…opposite)

pims/api/histograms.py

@@ -12,6 +12,7 @@
 #  * See the License for the specific language governing permissions and
 #  * limitations under the License.
 import itertools
+import operator
 from typing import List, Optional
 
 from fastapi import APIRouter, BackgroundTasks, Depends, Query, Response
@@ -25,7 +26,7 @@
 )
 from pims.api.utils.models import CollectionSize, HistogramType
 from pims.api.utils.parameter import imagepath_parameter
-from pims.api.utils.response import response_list
+from pims.api.utils.response import CustomOrJsonResponse, response_list
 from pims.files.file import HISTOGRAM_STEM, Path
 from pims.processing.histograms.utils import argmax_nonzero, argmin_nonzero, build_histogram_file
 from pims.utils.iterables import ensure_list
@@ -219,6 +220,10 @@ def show_channels_histogram(
     histograms = []
     n_bins = parse_n_bins(hist_config.n_bins, len(in_image.value_range))
     htype = in_image.histogram_type()
+
+    # hist_filter = operator.itemgetter(*channels)
+    # channels_bounds = hist_filter(in_image.channels_bounds())
+    # channels_histograms = hist_filter(in_image.channel_histogram()) TODO
     for channel in channels:
         histograms.append(
             ChannelHistogram(
@@ -256,8 +261,10 @@ def show_channels_histogram_bounds(
 
     hist_info = []
     htype = in_image.histogram_type()
-    for channel in channels:
-        mini, maxi = in_image.channel_bounds(channel)
+    hist_filter = operator.itemgetter(*channels)
+    channels_bounds = hist_filter(in_image.channels_bounds())
+    for channel, bounds in zip(channels, channels_bounds):
+        mini, maxi = bounds
         hist_info.append(
             ChannelHistogramInfo(
                 channel=channel, type=htype,