Sven Neumann writes:
> If someone wants to try to recover some of the JPEG save settings
> when loading the JPEG file, feel free.
I did.
Index: plug-ins/jpeg/jpeg-load.c
===================================================================
--- plug-ins/jpeg/jpeg-load.c (revision 22905)
+++ plug-ins/jpeg/jpeg-load.c (working copy)
@@ -50,6 +50,61 @@
gint32 layer_ID_global;
+static gboolean
+check_table (const JQUANT_TBL *file_table,
+ gint quant_tbl_no,
+ gint *quality)
+{
+ int i;
+ gboolean all_ones = TRUE;
+ gint q;
+ struct jpeg_compress_struct cinfo;
+
+ /* First do the simple check for quality 100, a table with all ones */
+ for (i = 0; i < 64; i++)
+ {
+ if (file_table->quantval[i] != 1)
+ all_ones = 0;
+ }
+
+ if (all_ones)
+ {
+ *quality = 100;
+ return TRUE;
+ }
+
+ /* Then produce tables for all qualities 1..99 and compare. It's
+ * better to do it this way than to calculate the quality factor
+ * backwards from the table in the file because of rounding errors:
+ * We would never match all quality factors exactly.
+ */
+ for (q = 1; q < 100; q++)
+ {
+ jpeg_create_compress (&cinfo);
+
+ jpeg_set_quality (&cinfo, q, TRUE);
+
+ for (i = 0; i < 64; i++)
+ {
+ if (cinfo.quant_tbl_ptrs[quant_tbl_no]->quantval[i] !=
file_table->quantval[i])
+ break;
+ }
+
+ jpeg_destroy_compress (&cinfo);
+
+ if (i == 64)
+ break;
+ }
+
+ if (q < 100)
+ {
+ *quality = q;
+ return TRUE;
+ }
+
+ return FALSE;
+}
+
gint32
load_image (const gchar *filename,
GimpRunMode runmode,
@@ -57,6 +112,7 @@
{
GimpPixelRgn pixel_rgn;
GimpDrawable *drawable;
+ GimpParasite *parasite;
gint32 volatile image_ID;
gint32 layer_ID;
struct jpeg_decompress_struct cinfo;
@@ -76,6 +132,8 @@
GimpParasite * volatile comment_parasite = NULL;
jpeg_saved_marker_ptr marker;
gboolean found_exif = FALSE;
+ gint q0, q1, q2;
+ gint quality = -1;
/* We set up the normal JPEG error routines. */
cinfo.err = jpeg_std_error (&jerr.pub);
@@ -153,6 +211,32 @@
(void) jpeg_read_header (&cinfo, TRUE);
+ /* Check if the quantization tables used are produced by libjpeg's
+ * jpeg_set_quality().
+ */
+
+ if ((cinfo.jpeg_color_space == JCS_GRAYSCALE &&
+ check_table (cinfo.quant_tbl_ptrs[cinfo.comp_info[0].quant_tbl_no],
+ cinfo.comp_info[0].quant_tbl_no,
+ &q0)) ||
+ (cinfo.jpeg_color_space == JCS_YCbCr &&
+ check_table (cinfo.quant_tbl_ptrs[cinfo.comp_info[0].quant_tbl_no],
+ cinfo.comp_info[0].quant_tbl_no,
+ &q0) &&
+ check_table (cinfo.quant_tbl_ptrs[cinfo.comp_info[1].quant_tbl_no],
+ cinfo.comp_info[1].quant_tbl_no,
+ &q1) &&
+ q0 == q1 &&
+ (cinfo.comp_info[1].quant_tbl_no == cinfo.comp_info[2].quant_tbl_no ||
+ (check_table (cinfo.quant_tbl_ptrs[cinfo.comp_info[2].quant_tbl_no],
+ cinfo.comp_info[2].quant_tbl_no,
+ &q2) &&
+ q1 == q2))))
+ {
+ /* Yes. Store the quality in a parasite below. */
+ quality = q0;
+ }
+
/* We can ignore the return value from jpeg_read_header since
* (a) suspension is not possible with the stdio data source, and
* (b) we passed TRUE to reject a tables-only JPEG file as an error.
@@ -257,6 +341,14 @@
layer_type, 100, GIMP_NORMAL_MODE);
}
+ if (quality > 0)
+ {
+ parasite = gimp_parasite_new ("jpeg-original-quality",
+ 0, sizeof (gint), &quality);
+ gimp_image_parasite_attach (image_ID, parasite);
+ gimp_parasite_free (parasite);
+ }
+
drawable_global = drawable = gimp_drawable_get (layer_ID);
gimp_pixel_rgn_init (&pixel_rgn, drawable, 0, 0,
drawable->width, drawable->height, TRUE, FALSE);
Index: plug-ins/jpeg/jpeg.c
===================================================================
--- plug-ins/jpeg/jpeg.c (revision 22905)
+++ plug-ins/jpeg/jpeg.c (working copy)
@@ -428,6 +428,23 @@
* over the JPEG encoding parameters.
*/
run_mode = GIMP_RUN_INTERACTIVE;
+
+ /* If we have stored an estimate of the libjpeg quality
+ * factor used when creating the original image, and
+ * that is larger than the default quality, use it as
+ * default for the dialog.
+ */
+ parasite = gimp_image_parasite_find (orig_image_ID,
+ "jpeg-original-quality");
+ if (parasite)
+ {
+ gint quality;
+ memmove (&quality, gimp_parasite_data (parasite), sizeof
(gint));
+ gimp_parasite_free (parasite);
+
+ if (quality > jsvals.quality)
+ jsvals.quality = quality;
+ }
}
break;
}
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