when importing pdf/eps there are compression artefacts in bitmaps embedded in the pdf/eps
Dear all,
maybe this is a feature request, bug, or simply a question, so I put it onto this mailing list:
When I import an eps that contains a bitmap (e.g. an eps generated from a MATLAB figure, that also has an image displayed), the bitmap in the imported form does not show the original pixels anymore but suffers from compression artefacts. These artefacts are not very visible for large image with small pixels relative to the total image size.
However, I often need to display zoomed regions of microscopy image, where those compressions are having quite a detrimental effect on the import. As an example I created a MATLAB figure with 10x10 random pixels. I attach the svg file where I imported the MATLAB figure after saving it as a PNG within MATLAB and another import of the eps file that I saved with MATLAB. The artefacts are clearly visible. ;)
Most times the compression is probably great to reduce overall file size, but in occasions like the ones described above it would be great to have a different or no compression of the bitmaps during import.
Many thanks, Enno
Just to add to my other e-mail: if I import the 10x10 image saved as a PNG for itself and not part of the matlab figure, the 10x10 imported bitmap also suffers artefacts (see updated attached svg) Maybe there are some settings to avoid this? Best, Enno
On Wed, Oct 14, 2015 at 8:36 AM, Enno R. Oldewurtel < enno.oldewurtel@...155...> wrote:
Dear all,
maybe this is a feature request, bug, or simply a question, so I put it onto this mailing list:
When I import an eps that contains a bitmap (e.g. an eps generated from a MATLAB figure, that also has an image displayed), the bitmap in the imported form does not show the original pixels anymore but suffers from compression artefacts. These artefacts are not very visible for large image with small pixels relative to the total image size.
However, I often need to display zoomed regions of microscopy image, where those compressions are having quite a detrimental effect on the import. As an example I created a MATLAB figure with 10x10 random pixels. I attach the svg file where I imported the MATLAB figure after saving it as a PNG within MATLAB and another import of the eps file that I saved with MATLAB. The artefacts are clearly visible. ;)
Most times the compression is probably great to reduce overall file size, but in occasions like the ones described above it would be great to have a different or no compression of the bitmaps during import.
Many thanks, Enno
On 2015-10-14 08:36 (+0200), Enno R. Oldewurtel wrote:
When I import an eps that contains a bitmap (e.g. an eps generated from a MATLAB figure, that also has an image displayed), the bitmap in the imported form does not show the original pixels anymore but suffers from compression artefacts. These artefacts are not very visible for large image with small pixels relative to the total image size.
However, I often need to display zoomed regions of microscopy image, where those compressions are having quite a detrimental effect on the import. As an example I created a MATLAB figure with 10x10 random pixels. I attach the svg file where I imported the MATLAB figure after saving it as a PNG within MATLAB and another import of the eps file that I saved with MATLAB. The artefacts are clearly visible. ;)
Most times the compression is probably great to reduce overall file size, but in occasions like the ones described above it would be great to have a different or no compression of the bitmaps during import.
See the discussion e.g. in the comments of this report: * “Interpolation while viewing in-file bitmap image” https://bugs.launchpad.net/inkscape/+bug/1418038
It should cover the new rendering options for bitmap images in Inkscape 0.91, both when importing a bitmap image directly, as well as when importing foreign vector formats with embedded bitmap data.
As workaround for bitmap images embedded in imported EPS/PS files in Inkscape 0.91, you can install and use the extension attached to this report: * https://bugs.launchpad.net/inkscape/+bug/1357808 (The extension will be available as 'Extensions > Images > Set Image Attributes'; just enable "[x] Render images blocky" on the 'Basic' tab, and apply)
Also related (see comments 11 and 12): * “discrete color scale bitmap becomes continuous object after eps/pdf export” https://bugs.launchpad.net/inkscape/+bug/1174651
hth, V
Thank you so much. This helps a lot. I have not played with the extension yet, but simply setting the object properties solves things, too. For some reason I always thought optimizeQuality would lead to a "high quality" appearance of the correct display, instead of switching the rendering to optimizeSpeed.
Just for my own understanding: This object property is something that gets saved when exporting the svg to a pdf or eps again, correct? Do pdf/eps viewer then render the bitmap according to whichever property was set? Does that mean that eps/pdf viewer which do not read this property, might render the bitmap with interpolations again, i.e. depending on the viewer program the bitmap might appear blocky or smoothed? That would also mean that the original image/pixel information always gets exported to pdf/eps, but it is only the rendering which make them appear differently, correct?
Ideally, I would like to produce eps and pdf that will always show the bitmaps blocky (at least when having a zoomed image with very large pixels), independent of the viewer program.
Thanks a lot! Enno
On Wed, Oct 14, 2015 at 4:24 PM, su_v <suv@...2638...> wrote:
On 2015-10-14 08:36 (+0200), Enno R. Oldewurtel wrote:
When I import an eps that contains a bitmap (e.g. an eps generated from a MATLAB figure, that also has an image displayed), the bitmap in the imported form does not show the original pixels anymore but suffers from compression artefacts. These artefacts are not very visible for large image with small pixels relative to the total image size.
However, I often need to display zoomed regions of microscopy image, where those compressions are having quite a detrimental effect on the import. As an example I created a MATLAB figure with 10x10 random pixels. I attach the svg file where I imported the MATLAB figure after saving it as a PNG within MATLAB and another import of the eps file that I saved with MATLAB. The artefacts are clearly visible. ;)
Most times the compression is probably great to reduce overall file size, but in occasions like the ones described above it would be great to have a different or no compression of the bitmaps during import.
See the discussion e.g. in the comments of this report:
- “Interpolation while viewing in-file bitmap image” https://bugs.launchpad.net/inkscape/+bug/1418038
It should cover the new rendering options for bitmap images in Inkscape 0.91, both when importing a bitmap image directly, as well as when importing foreign vector formats with embedded bitmap data.
As workaround for bitmap images embedded in imported EPS/PS files in Inkscape 0.91, you can install and use the extension attached to this report:
(The extension will be available as 'Extensions > Images > Set Image Attributes'; just enable "[x] Render images blocky" on the 'Basic' tab, and apply)
Also related (see comments 11 and 12):
- “discrete color scale bitmap becomes continuous object after eps/pdf
export” https://bugs.launchpad.net/inkscape/+bug/1174651
hth, V
Inkscape-user mailing list Inkscape-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/inkscape-user
On 2015-10-14 16:59 (+0200), Enno R. Oldewurtel wrote:
Just for my own understanding:
This object property is something that gets saved when exporting the svg to a pdf or eps again, correct?
Confirmed for PDF, not tested with PostScript format (unknown to me whether PostScript does know such a interpolation mode for bitmap images, as also mentioned by Jasper in bug #1174651).
Do pdf/eps viewer then render the bitmap according to whichever property was set?
Again, locally only tested with PDF files (and a limited varity of PDF viewers) - results seem to depend on the PDF viewer: - works with Evince 3.16.1, poppler 0.36 - fails with Apple's Preview.app on OS X 10.7.5 Lion (outdated!) - works with Evince 2.30.3, poppler 0.18 (outdated!)
Does that mean that eps/pdf viewer which do not read this property, might render the bitmap with interpolations again, i.e. depending on the viewer program the bitmap might appear blocky or smoothed?
I don't know - you'd have to check details about the specific PDF viewer, as well as whether the PDF specs possibly include details about what to expect if a viewer does not support flags like 'interpolate'. The specific optional interpolation mode for images in PDF files is is already described in the oldest PDF spec available at Adobe's site (PDF Reference, Second Edition, version 1.3 from Jul 3 2000):
Image Interpolation
When the resolution of a source image is significantly lower than that of the out- put device, each source sample covers many device pixels. This can cause images to appear “jaggy” or “blocky.” These visual artifacts can be reduced by applying an image interpolation algorithm during rendering. Instead of painting all pixels covered by a source sample with the same color, image interpolation attempts to produce a smooth transition between adjacent sample values. Because it may increase the time required to render the image, image interpolation is disabled by default; setting the Interpolate entry in the image dictionary to true enables it.
Note: The interpolation algorithm is implementation-dependent and is not specified by PDF. Image interpolation may not always be performed for some classes of images or on some output devices.
(identical text e.g. in PDF 1.3 and PDF 1.5 spec - Inkscape defaults to PDF 1.5 for export).
A quick web search finds results like e.g. http://superuser.com/questions/358134/pdf-rendering-of-images-seems-to-vary-... (it's from 2011, I can't tell whether the situation has improved since then)
That would also mean that the original image/pixel information always gets exported to pdf/eps, but it is only the rendering which make them appear differently, correct?
Yes (AFAIU bug #168434 for PNGs was fixed a long time ago, bug #168708 for JPEGs is fixed in Inkscape 0.91).
Ideally, I would like to produce eps and pdf that will always show the bitmaps blocky (at least when having a zoomed image with very large pixels), independent of the viewer program.
Based on the original topic of this thread ("Subject: when importing pdf/eps (...)"): Please keep in mind that round-trip editing PDF (or PS/EPS) files with Inkscape is not guaranteed to keep appearance 100% identical - the quality might degrade over time (with each round-trip editing) depending on the actual original content (and content added in Inkscape), since the file formats (PDF/PostScript/SVG) differ in how which set of features are supported (not just image rendering mode).
Inkscape's import and export of PDF- and PostScript-based file formats depend on external tools and libraries, so apart from bugs or missing features in Inkscape itself (plenty of those), any upstream issues in specific versions of ps2pdf from Ghostscript (PS/EPS -> PDF)[1], poppler (PDF -> SVG) and cairo (SVG -> PDF/PS/EPS) might additionally affect results.
hth, V
[1] Inkscape's PS/EPS import uses ps2pdf from Ghostscript to convert the PostScript-based files to PDF, and them imports the PDF file using internal routines (based on poppler as parser). Export to PostScript-based formats OTOH is handled internally, based on cairo.
participants (2)
-
Enno R. Oldewurtel -
su_v