Image scroll producer does not work as expected

[CasparCGImport]

Converted from SourceForge issue 3560165, submitted by zebiolo

Image scroller producer does not work as expected (starts at a strange position in the image). Needs a general overhaul.

[CasparCGImport]

Submitted by hummelstrand

This needs to be documented in the wiki!

[CasparCGImport]

Submitted by hellgore

Image Scroll Producer

Changes

• The SPEED parameter is now expressed as pixels to move per frame/field. Previously it was expressed as number of half pixels to move per frame.
• The scrolling direction is now reversed so that a positive speed is now correct for an ordinary end credits roll.
• Previously both fields in interlaced video formats represented the same temporal image position causing unsmooth film like motion. This has now been corrected so that both fields represents two different temporal image positions for smooth field-rate motion instead of frame-rate motion.
• A PROGRESSIVE parameter can be given to suppress the smooth motion, so it will once again move in the frame rate instead of the field rate.
• The image now starts at a position just outside of the screen and ends at a position just outside of the screen. Previously it started at a strange somewhere in the middle of the image position for end credit rolls.
• The SPEED parameter now is a decimal value instead of an integer value. using a value of for example 0.5 will move the image one half pixel each frame/field placed with subpixel accuracy. SPEED 0.5 is the previous equivalent of SPEED -1 since the speed previously was measured in half pixels instead of pixels.
• The producer now internally is more exact in the positioning of each frame/field. Previously the image could be placed a little bit "off" because of double precision rounding errors which could make the image being rendered in between two pixels with subpixel accuracy once in a while even though speed was 2 or more (no half pixels should be involved).
• A new parameter PREMULTIPLY has been added to preprocess the loaded image by premultiplying the color channels with alpha channel in case that the image was not saved that way.
• Motion blur support has been added via the parameter BLUR which can be useful to counteract interline twitter in interlaced video formats.

Recommendations

• For interlaced video formats always use an even speed value (2, 4, 8, 10 etc). The reason for this is that otherwise the image will loose half of its vertical resolution while scrolling. This is only important when scrolling vertically though (credit rolls for example).
• For interlaced video scrolling vertically, don't use thin (vertically) and sharp details, because it will flicker during scrolling (interline twitter).
• Apply a slight motion blur in the direction where the image is supposed to be scrolled, this will reduce the flickering effect but loose some detail. This can be done by Caspar on loading the image via the BLUR parameter but it will add to the load time (filtering speed is related to the number of pixels to blur).
• Images are sometimes stored with straight alpha by image editors. If so the PREMULTIPLY parameter must be given in order for Caspar to perform as expected when rendering.
• For progressive video formats the speed value can have uneven values or even values without a problem with vertical resolution.
• Don't use decimal speed values unless 1 pixel per frame/field is too fast, because the brightness of details in the image might appear to change when the image is placed with subpixel accuracy between two pixels.

[CasparCGImport]

Submitted by hummelstrand

Does this documentation relate to "2.0 stable" or is this something that has been changed after that release? We have nothing in the wiki about this feature, I'm planning on putting it in http://casparcg.com/wiki/CasparCG_Server#Image_Producer as soon as I can get a confirmation that it works in the released version.

[CasparCGImport]

Submitted by hummelstrand

I'd also like to get a good syntax description with a few examples.

[CasparCGImport]

Submitted by hellgore

This functionality is not yet released, but is committed to trunk at this point.

I attached a file instead for easier reading (fixed width font in tracker comments might be possible but I don't know how)

[CasparCGImport]

Submitted by hellgore

I will add some examples to the text document

[CasparCGImport]

Submitted by hellgore

There is now examples in the attached file

[CasparCGImport]

Submitted by zebiolo

This feature will be included in the next release.

[CasparCGImport]

Submitted by hellgore

Ready for test