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Advanced Settings

Basic system config options such as the thumbnail image quality can be changed on the advanced settings page. You can also disable specific features and enable the debug or read-only mode.

For security reasons, the advanced settings page is disabled and hidden when the public mode is enabled.

Changing advanced settings always requires a restart to take effect. Selecting a different thumbnail quality or size won't replace existing thumbnails. You may regenerate them using the command-line interface.

The same options can all be set using their corresponding config options instead. Settings are saved in the storage/config directory.

Options

Debug Logs

When enabled, debug logs are shown in Library>Logs. Requires restart.

The equivalent config toggle is PHOTOPRISM_DEBUG.

Read-only Mode

When enabled, importing, uploading and deleting files is not possible.

The equivalent config toggle is PHOTOPRISM_READONLY.

Experimental Features

When enabled, your instance will be updated with experimental features.

The equivalent config toggle is PHOTOPRISM_EXPERIMENTAL.

Disable Backups

This option prevents creating the following yml backups:

  • For photos in storage/sidecar
  • For albums, months, states and folders in storage/albums

The equivalent config toggle is PHOTOPRISM_DISABLE_BACKUPS.

Disable WebDAV

This option prevents building WebDav connections. Requires restart for changes to be applied.

The equivalent config toggle is PHOTOPRISM_DISABLE_WEBDAV.

Disable Places

When selected, geo-information (latitude, longitude) will still be read (and indexed) from your files metadata, however PhotoPrism will not use reverse lookup to determine place names using those coordinates as it normally would.

The Places section will not be visible.

The equivalent config toggle is PHOTOPRISM_DISABLE_PLACES.

Disable ExifTool

This option prevents the creation of json files with Exif data in storage/sidecar.

The equivalent config toggle is PHOTOPRISM_DISABLE_EXIFTOOL.

Disable TensorFlow

When selected, image classification / object detection (using TensorFlow) is disabled, so no labels are created for your files.

The equivalent config toggle is PHOTOPRISM_DISABLE_TENSORFLOW.

Images

This section controls how original files are converted to JPEG for use as thumbnails and image previews.

Downscaling Filter

This selects the algorithm used to generate downsampled JPEG preview images ('thumbnails') from original files.

For best quality thumbnails, choose the lanczos downscaling filter, which is slow to process (during thumbnail generation) but generates higher quality thumbnails. By comparison, the cubic filter may be 30% faster. See section below for detailed description of available filters.

The equivalent config option is PHOTOPRISM_THUMB_FILTER.

Dynamic Previews

Enable generating thumbnails on-the-fly as they're required (either for viewing or analysing with TensorFlow). This saves disk space, but is more processor-intensive and so not recommended when hosting on less powerful devices (such as Raspberry Pi).

The equivalent config toggle is PHOTOPRISM_THUMB_UNCACHED.

JPEG Quality

Choose a value above 90 to display your images in the best possible quality. Note that higher values require more space in the storage folder for less compressed thumbnail files, which may also take longer to create.

Lower quality thumbnails, on the other hand, are smaller, load faster on slow Internet connections, and require less space in the storage folder and in the browser cache.

  • Quality levels of 90% or higher are generally considered high quality
  • 80% to 90% is considered medium quality
  • 70% to 80% is considered low quality, as you might see with highly compressed content on social media

Anything below 70% is generally of very low quality.

Example: If a quality of 95 results in a thumbnail file size of 500kB, then reducing the quality to 80 reduces the file size to about 100kB.

The equivalent config option is PHOTOPRISM_JPEG_QUALITY.

The actual impression depends on how much information an image contains. Empty areas and skies, for example, are easier to compress. Images with a lot of details suffer the most. For this reason, reducing the quality of thumbnails also negatively impacts facial recognition and image classification results. Simply put, this means that the indexer sees fewer details.

Dynamic and Static Size Limits

Dynamic Size Limit: During dynamic (on-demand) thumbnail generation, no thumbnails will be created above this size. The equivalent config option is PHOTOPRISM_THUMB_SIZE_UNCACHED.

Static Size Limit: During initial indexing or import (as thumbnails are generated), no thumbnails will be created above this size. The equivalent config option is PHOTOPRISM_THUMB_SIZE.

Reducing the Static Size Limit of thumbnails has a significant impact on facial recognition and image classification results. Simply put, it means that the indexer can no longer see properly.

If the configured size limit is exceeded (for example, if users have a larger screen), a sufficiently large thumbnail can't be created, and the photo viewer may be forced to display the original image instead. Downscaling images in browsers typically results in poor quality, and they may also be displayed in the wrong orientation.

The smallest configurable size is 720px for consumption by the indexer to perform color detection, face detection, and image classification. Recreating them every time they are needed is too demanding for even the most powerful servers. Unless you only have a few small images, it would render the app unusable.

It is recommended that you set these limits high so that browsing pictures is as smooth as possible. However, if the amount of disk storage required is a serious problem, and you are willing to increase server load instead, it is possible to set the Static Size Limit to the minimum of 720px in combination with a higher Dynamic Size Limit. This allows the server to generate larger thumbnails on demand. It may also result in a noticeable delay when viewing pictures in full-screen mode.

To view original images, enable Dynamic Previews, and configure Dynamic Size Limit and Static Size Limit to a small value like 720. When viewing images exceeding that limit, the original files will be displayed.

What files will be created by PhotoPrism?

The minimum size for static previews is 720px, so all images up to 720x720 will be rendered. Higher static limits will additionally generate previews only up to the defined limit.

The files are generated in the storage/cache/thumbnails folder, with file paths dependent on the size and original file's hash, such as:

storage/cache/thumbnails/1/a/3/1a30c1f...9_100x100_center.jpg

The table below shows each generated size, with the PhotoPrism features using each.

Name Width Height Use
colors 3 3 Color Detection
tile_50 50 50 List Preview
tile_100 100 100 Maps Preview
tile_224 224 224 Mosaic Preview
left_224 224 224 TensorFlow
right_224 224 224 TensorFlow
tile_500 500 500 Cards Preview
fit_720 720 720 Mobile, TV
fit_1280 1280 1024 Mobile, HD Ready TV
fit_1920 1920 1200 Mobile, Full HD TV
fit_2048 2048 2048 Tablets, Cinema 2K
fit_2560 2560 1600 Quad HD, Retina Display
fit_3840 3840 2400 Ultra HD
fit_4096 4096 4096 Ultra HD, Retina 4K
fit_7680 7680 4320 8K Ultra HD 2, Retina 6K

Downscaling Filters

Linear

Bilinear interpolation takes a weighted average of the four neighborhood pixels to calculate its final interpolated value. The result is a much smoother image than the original image. When all known pixel distances are equal, then the interpolated value is simply their sum divided by four. This technique performs interpolation in both directions, horizontal and vertical. This technique gives better result than nearest neighbor interpolation and take less computation time compared to bicubic interpolation.

Cubic

Catmull-Rom is a local interpolating spline developed for computer graphics purposes. Its initial use was in design of curves and surfaces, and has recently been used in several applications. Catmull-Rom splines are a family of cubic interpolating splines formulated such that the tangent at each point is calculated using the previous and next point on the spline. The results are similar to ones produced by bicubic interpolation with regards to sharpness, but the Catmull-Rom reconstruction is clearly superior in smooth signal region.

Lanczos

The Lanczos interpolation function is a mathematical formula used to smoothly interpolate the value of a digital image between its samples. It maps each sample of the given image to a translated and scaled copy of the Lanczos kernel, which is a sinc function windowed by the central hump of a dilated sinc function. The sum of these translated and scaled kernels is then evaluated at the desired pixel. Lanczos interpolation has the best properties in terms of detail preservation and minimal generation of aliasing artifacts for geometric transformations not involving strong down sampling. However higher order Lanczos interpolation requires high computational time, which makes it unsuitable for most commercial software.

Blackman

Blackman is a modification of Lanczos that has better control of ringing artifacts.

Examples

Original image:

The same image resized from 600x400px to 150x100px using different resampling filters. From faster (lower quality) to slower (higher quality):

Filter Resize result
Nearest Neighbor
Bilinear
Sharp Bicubic
Lanczos

Source: A Comparative Analysis of Image Interpolation Algorithms

RAW Conversion

Many photographers keep their originals in some sort of lossless RAW format instead of compressed JPEG, especially when shooting with a Digital SLR. Some mobile phones also support RAW or use HEIC/HEIF for a similar purpose. PhotoPrism aims at providing excellent support for all RAW formats, independent of camera brand and model. Please let us know when there is an issue with your specific device.

Web browsers in general cannot display RAW image files. They need to be converted, which is what our import and convert commands do. You'll also find a checkbox for this step in our Web UI.

In addition, PhotoPrism also supports TIFF, PNG, BMP and GIF files. Be aware that files in those formats often don't contain useful metadata and are typically used for screenshots, charts, graphs and icons only.

Generated sidecar files will be stored outside your originals folder by default, so that RAW to JPEG conversion also works in read-only mode.

JPEG Size Limit

This controls the maximum size of downsampled JPEG preview files to create when converting original RAW images.

The equivalent config toggle is PHOTOPRISM_JPEG_SIZE.

Use Presets

Disables simultaneous conversion of RAW files to apply Darktable presets.

The equivalent config toggle is PHOTOPRISM_RAW_PRESETS.

Disable Darktable

When disabled Darktable won't be used for RAW conversion.

The equivalent config toggle is PHOTOPRISM_DISABLE_DARKTABLE.

Disable RawTherapee

When disabled RawTherapee won't be used for RAW conversion.

The equivalent config toggle is PHOTOPRISM_DISABLE_RAWTHERAPEE.

Disable FFmpeg

When disabled FFmpeg won't be used for video transcoding.

The equivalent config toggle is PHOTOPRISM_DISABLE_FFMPEG.