docs: improve remarks about lossy JBIG2 and lossy image transformations

docs/advanced.rst

@@ -223,7 +223,9 @@ The ``hocr`` renderer
 The ``hocr`` renderer works with older versions of Tesseract. The image
 layer is copied from the original PDF page if possible, avoiding
 potentially lossy transcoding or loss of other PDF information. If
-preprocessing is specified, then the image layer is a new PDF.
+preprocessing is specified, then the image layer is a new PDF. (You may
+need to disable PDF/A conversion nad optimization to eliminate all
+lossy transformations.)
 
 Unlike ``sandwich`` this renderer is implemented within OCRmyPDF; anyone
 looking to customize how OCR is presented should look here. A major

docs/cookbook.rst

@@ -340,6 +340,9 @@ levels in the GCC compiler.
         - Enables lossless optimizations, such as transcoding images to more
           efficient formats. Also compress other uncompressed objects in the
           PDF and enables the more efficient "object streams" within the PDF.
+          (If ``--jbig2-lossy`` is issued, then lossy JBIG2 optimization is used.
+          The decision to use lossy JBIG2 is separate from standard optimization
+          settings.)
     *   - ``--optimize 2``
         - All of the above, and enables lossy optimizations and color quantization.
     *   - ``--optimize 3``
@@ -360,3 +363,8 @@ fo a PDF.
     ocrmypdf --optimize 3 in.pdf out.pdf  # Make it small
 
 Some users may consider enabling lossy JBIG2. See: :ref:`jbig2-lossy`.
+
+.. note::
+
+    Image processing and PDF/A conversion can also introduce lossy transformations
+    to your PDF images, even when ``--optimize 1`` is in use.