RawTherapee 5.6 on Mac OS 10.14.4: Low quality Editor Preview

Hi, I’ve been an avid user of rawTherapee for a couple of months, and I really like what you have created. Well done.

The Editor’s Preview only shows a low quality image compared to other applications. Making it very hard to judge the overall quality of the image. I have to export the image to be able to see the overall quality compared to other applications (Bridge, Capure One) where I can see the full quality preview. Specifically, set the zoom of an image to fill (shortcut f). Open the same image in another application e.g. Adobe bridge, and scale the preview there to the same size as in rawTherapee. We can now compare the previews, and rawTherapee’s lacks much clarity, (it seems that the resolution is reduced). There isn’t a problem in any other case.
Is this a bug or an intended feature, and can I do anything to fix this?.

I’m not talking about seeing any adjustments, e.g. some require 100% zoom, but seeing the whole full quality image in the Editor Preview. I can see the quality degradation of the Preview at zoomed out.

I’ve created these screenshots on a MacBook Pro (13-inch, Late 2016), running the latest version of rawTherapee 5.6 and

Adobe Bridge. Screenshots Taken with CMD+Shift+3 (capture full screen).

18.5.0 Darwin Kernel Version 18.5.0: Mon Mar 11 20:40:32 PDT 2019; root:xnu-4903.251.3~3/RELEASE_X86_64 x86_64
macOS Mojave 10.14.4
MacBook Pro (13-inch, Late 2016) ( with Retina display )
Screen: 13.3”, 2,560 × 1,600, 227 ppi with Wide colour (P3) gamut, 500-[nits] (13")
Display Type:|Built-In Retina LCD
Resolution:|2560x1600 Retina
Framebuffer Depth:|24-Bit Colour (ARGB8888)

Version: 5.6
Branch: 5.6
Commit: 5a4ed7317
Commit date: 2019-04-20
Compiler: clang
Processor: generic x86
System: Apple
Bit depth: 64 bits
Gtkmm: V3.24.1
Lensfun: V0.3.95.0
Build type: release
Build flags: -std=c++11 -std=c++11 -mtune=generic -Werror=unused-label -mmacosx-version-min=10.9 -flto -Wall -Wuninitialized -Wno-deprecated-declarations -Wno-unused-result -Xpreprocessor -fopenmp /opt/local/lib/libiomp5.dylib -I/opt/local/include -Werror=unknown-pragmas -O3 -DNDEBUG -ftree-vectorize
Link flags: -mtune=generic -headerpad_max_install_names -flto
OpenMP support: ON
MMAP support: ON

See point 9 in the Advanced section:
It applies to everything, not only the transform tools.

So if I undersand you/the documentation correctly the preview will always be of a small size unless you are at 100%.

I understand the rationale of having a smallish preview to make the rendering go faster when you have many layers of tools.
But I believe that the option change the sized of the rendered preview, to fully use the screen, would be helpful, especially when reviewing/culling your images.

The developers probably had good intention for choosing the rescaling of the preview image.
Depending on goal of the resizing, this could a bug. For example if the preview size (pixels) should approximate the size (pixels) on the screen.
It looks like result of the current implementation chooses the preview 1/4 size (halved length and width) of the area used to draw it on the screen, then the display?/graphics card? extrapolates it to be drawn on the screen. See the photos:

Bridge Bridge_zoom

Raw (100%) RAW_ZOOM

Previous images where hard to see, I took a screenshot of them instead.
RawTherapee: Super smooth and nice.
Notice the 2x2 blotchiness from the extrapolation.

Bridge/Adobe Camera Raw:
Notice the noise but no 2x2 blotchiness.

The source image is shrunk to the size of the preview, and then most operations (not all) are performed on that little preview image. Tools such as Retinex operate on the full image (for technical reasons), which is why manipulating them takes longer to update the preview. We would all like the situation to be different, but it is what it is for technical and historical reasons. Maybe one day it will change: Unify the various processing pipelines · Issue #3897 · Beep6581/RawTherapee · GitHub

Ah, then you might be referring to something else. Specifically, you might be encountering the HiDPI problem joyride. Try fiddling with “Pseudo-HiDPI” mode and with your macOS display scale/resolution: Preferences - RawPedia