much faster downscaling of JPEGs

diff --git a/images/io-libjpeg.c b/images/io-libjpeg.c
index f7458124d20383c650f7f81be32529ff5d6c71a9..876c1720131e0d36c07bcc387d18885c1464bb41 100644 (file)
--- a/images/io-libjpeg.c
+++ b/images/io-libjpeg.c
@@ -257,9 +257,29 @@ libjpeg_read_data(struct image_io *io)
        return 0;
     }
 
-  /* Prepare the image ... FIXME: use libjpeg feature to speed up downscale */
+  /* Prepare the image  */
   struct image_io_read_data_internals rdi;
-  if (unlikely(!image_io_read_data_prepare(&rdi, io, i->cinfo.image_width, i->cinfo.image_height, io->flags)))
+  if (io->cols <= (i->cinfo.image_width >> 3) && io->rows <= (i->cinfo.image_height >> 3))
+    {
+      DBG("Scaling to 1/8");
+      i->cinfo.scale_num = 1;
+      i->cinfo.scale_denom = 8;
+    }
+  else if (io->cols <= (i->cinfo.image_width >> 2) && io->rows <= (i->cinfo.image_height >> 2))
+    {
+      DBG("Scaling to 1/4");
+      i->cinfo.scale_num = 1;
+      i->cinfo.scale_denom = 4;
+    }
+  else if (io->cols <= (i->cinfo.image_width >> 1) && io->rows <= (i->cinfo.image_height >> 1))
+    {
+      DBG("Scaling to 1/2");
+      i->cinfo.scale_num = 1;
+      i->cinfo.scale_denom = 2;
+    }
+  jpeg_calc_output_dimensions(&i->cinfo);
+  DBG("Output dimensions %ux%u", (uns)i->cinfo.output_width, (uns)i->cinfo.output_height);
+  if (unlikely(!image_io_read_data_prepare(&rdi, io, i->cinfo.output_width, i->cinfo.output_height, io->flags)))
     {
       jpeg_destroy_decompress(&i->cinfo);
       return 0;

diff --git a/images/io-main.c b/images/io-main.c
index 15e76fbb57bef15337d9d995105c82f363164b20..03a36cc266305e310295938a54ac6bfae55360f6 100644 (file)
--- a/images/io-main.c
+++ b/images/io-main.c
@@ -264,7 +264,6 @@ image_io_read_data_finish(struct image_io_read_data_internals *rdi, struct image
       if (io->cols != rdi->image->cols || io->rows != rdi->image->rows)
         {
          DBG("Scaling image");
-         rdi->need_transformations = io->flags != rdi->image->flags;
          rdi->need_destroy = rdi->need_transformations || !io->pool;
          struct image *img = image_new(io->thread, io->cols, io->rows, rdi->image->flags, rdi->need_transformations ? NULL : io->pool);
          if (unlikely(!img))
@@ -286,7 +285,6 @@ image_io_read_data_finish(struct image_io_read_data_internals *rdi, struct image
       if ((io->flags ^ rdi->image->flags) & IMAGE_ALPHA)
         {
          DBG("Aplying background");
-         rdi->need_transformations = 0;
          rdi->need_destroy = rdi->need_transformations || !io->pool;
          struct image *img = image_new(io->thread, io->cols, io->rows, io->flags, rdi->need_transformations ? NULL : io->pool);
          if (unlikely(!img))
@@ -303,8 +301,6 @@ image_io_read_data_finish(struct image_io_read_data_internals *rdi, struct image
            }
          rdi->image = img;
        }
-
-      ASSERT(!rdi->need_transformations);
     }
 
   /* Success */