Image Sequence Formats

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Image Sequence Formats

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An image sequence is a series of sequential still images that represent frames of an animation. Commonly, the images are saved within one folder and are labeled with an incrementing file name in order to preserve the chronological order. They have the same pixel resolution, size and file format, whereas Pandoras Box supports .bmp, .jpg, .png and the graphics card texture format .dds. With version 5.7 we introduced the support of .snp files.
Please read the previous chapter Image Formats where - among other things - the difference between these formats is explained.

Most high-level programs like Adobe After Effects, Premiere Pro or 3D Studio Max are able to render an image sequence.

The advantages of working with image sequences

+ Quality
When rendering an animation as one single video you need to decide which codec should be used. Each codec must decide between high / low file size and low / high image quality. When rendering a png or bmp image sequence, no image information, e.g. color depth or resolution are discarded and thus the best possible quality is preserved. The downside is the file size.
A good balance is the dds format, eventhough it compresses the file size the quality does not suffer much. The dds format is a special texture format send directly to the graphics card without drawing performance from the bus and the processor. This way you may play back much more dds image sequences than with the other image formats. Please refer to the previous chapter, "Image Formats" for more information.
In addition, always depending on the kind of content, it possible to achieve better results regarding the quality than the mpeg video format can provide.

+ Alpha channel
Only few codecs support the alpha (transparency) channel. The recommended codec for Pandoras Box playback - mpg2 - only supports RGB. Transparent parts must be keyed out, for example with a masking effect and an according mask which can be generated using the Image Converter. When rendering a png or dds image sequence, you can decide to keep the alpha information.

+ Safety
When playing back a video you need to have the same codec installed that was used to render the video. When working with special / unusual codecs you have to keep in mind that they need to work platform independently and with good performance. When rendering and playing back an image sequence, no codecs are needed.

+ Flexibility
Most of the times content production starts before all hardware or technical decisions are made. In case of large scaled high-resolution softedge projections, for example, the total number of projectors might not be known, or the final projector positions are still in question. Cropping images or scaling them down with a batch program is far easier than editing a video. Please see other coolux tools Dome Master, Image Converter, and Splitter that are free of charge. Other image adjustments can be made e.g. with Adobe Photoshop.
Furthermore there might be limitations and misunderstandings regarding the communication between companies that participate in the same project. Sometimes there is no direct contact between the content creator and the operator or other companies within the production chain. In some cases it is a safer or more confident workflow for them to receive an image sequence and either do the final rendering process with one of our above mentioned tools or - since version 5.3 - to playback the image sequence directly in Pandoras Box.

The disadvantages of working with image sequences

- File Size
Bmp image sequences preserve the best image quality possible thus no information is compressed or discarded. That increases the entire system requirements regarding file transfer and memory. The critical question for a smooth playback is definitely the number of pixels per frame and the number of file accesses per second.

- Decompression
Png and jpg sequences compress the image's information in order to get a smaller file size. When being played back, the system need to decompress each single frame. Here not only the number of file accesses per second is critical, but also the processor's performance consumption due to decompression. For that reason we recommend to use bmp sequences. If you like to playback png or jpg sequences you might want to alter the number of threads used, this is described below.

It is recommended to use image sequences in Pandoras Box with SSD drives as normal hard drives are slower regarding the number of file accesses per second. If you do not necessarily need to change individual frames during playback it is a very good and recommended workflow to render an uncompressed avi at the very end of the content production; you may use the Image Converter for example. The avi format combines all advantages but as it is only one file, the system will be able to load it faster and the playback requires less performance.

How to use an image sequence in Pandoras Box

Just like any other file an image sequence must be first added from the Asset tab into the Project tab. It is recommended to save all images belonging to one sequence within one folder as well as to remove all other images (and other files, e.g. .dsstore, indexing files added automatically from MAC operating systems) not belonging to the sequence from this folder! In order to add the image sequence you cannot simply drag the folder, as this would generate a folder with multiple files. Right-click on the folder within the Assets tab and choose "Import As Image Sequence". A dialog opens and asks for the frame rate; depending on how the content was created enter for example 25fps or 30fps. As seen below, at this time a new resource with the sequence icon was added to the Project tab.
A second way to add a sequence to the project would be to right-click in your Project tab, choose "Add Image Sequence" and attach a sequence using the Inspector.


Now you can start programming with the image sequence by dragging the sequence from the Project tab into the timeline or by assigning it to a layer via double-click after selecting one in the Device Tree tab. If the sequence does not play back fluently, you can activate "Fluid Frame" in the Inspector (select the sequence in the Project tab to see its information in the Inspector). As well you can choose another setting in the text field "Number of Threads". The other options are explained in the topic "Image Sequence Inspector".

The number of threads influence how many threads are called by the Pandoras Box application from the operating system in order to run the sequence. There is no rule of thumb how many threads are the best. A higher number of threads can make the sequence run more smoothly and at the same time a too large number can make the playback more stuttery. There is no definite minimum or maximum. It depends on your hardware, e.g. the processor and type of hard drives. Regarding bmp sequences the default setting of 5 will give you good results. As png and jpg sequences require more processor performance, another thread number can give you better results. The optimal number depends on their compression rate.
Please make sure that the threat number is smaller than the total number of images in the sequence.

Tips for the workflow for image sequences

Before using image sequences in Pandoras Box...:

- Check the file names:
 best is to name all files with the same number of characters, in other words, if you have 100 files, the first one should be named image001 instead of "image"

- Delete additional files from the folder:
 best is to have a folder including the same number of files as images (there should be no thumbs file, notes or administration data)

- Name the folder with the frame rate:
 best is to have a folder including the frame rate the image sequence was rendered out for, e.g. "Stars_25fps"; ask the content creator to do that for you; this way you will later on, know for sure with which frame rate the image sequence should be imported


The previous topics describe the display and content formats in general, how to define the content resolution and provide an output resolution table. Please click these links, if you are interested in other content formats, such as audio, single images and videos.