Some Transparent Images Does Not Work

[susanto_tm]

I am currently making a design in inDesign and I am importing some transparent images. In the past it works by Ctrl + D the pictures into my placeholders, but this time instead of a transparent background, it shows an "orange"-like background in what supposed to be the transparent "part". What should I do to fix this?

[BobLevine]

What is the format of the image? What version of InDesign? What operating system? Is the frame filled with a color?

[susanto_tm]

I am using a PNG-8 (dithered) format for the picture. The version of my inDesign is the 2018 (13.0) version. I am using a Windows 10 Pro Build 16299 64-bit. The whole background is filled with this color except for the object in the picture.

[Steve Werner]

Try resaving the PNG in Photoshop. Some applications seem to create non-standard PNG files.

[susanto_tm · Accepted solution]

It works now -- I tried saving it as a PNG-24 instead and for some reason it works.

[Steve Werner]

PNG-24 supports transparency, PNG-8 does not.

[Dave Creamer of IDEAS]

Technically, PNG-8 supports one level of transparency; PNG-24 supports 256 levels of transparency.

[Steve Werner]

Yes, that's a more accurate description, thanks.

[Jongware]

IDEAS-Training  wrote

Technically, PNG-8 supports one level of transparency; PNG-24 supports 256 levels of transparency.

No, PNG-8 also allows more levels within a single image. (You probably mean that Photoshop does not support it. That's something different.)

[Dave Creamer of IDEAS]

Thank you, Jongware for clarifying--yes, I was thinking of Photoshop. If I remember, it supports 16 levels (2^4)--is that correct?

[Jongware]

The official specifications state that for every color index you can add an individual amount of transparency:

For color type 3 (indexed color), the tRNS chunk contains a series of one-byte alpha values, corresponding to entries in the PLTE chunk:

Alpha for palette index 0: 1 byte

Alpha for palette index 1: 1 byte

...etc...

You can deduce where the orange background in OP's image came from: the original palette color is orange and is picked up by InDesign, and the associated tRNS value is totally ignored.

The specifications do mention a minimum, but funny enough no maximum:

The tRNS chunk must not contain more alpha values than there are palette entries, but tRNS can contain fewer values than there are palette entries. In this case, the alpha value for all remaining palette entries is assumed to be 255. In the common case in which only palette index 0 need be made transparent, only a one-bytetRNS chunk is needed.

(PNG Specification: Chunk Specifications , 4.2.1.1 tRNS Transparency)

It comes down to "all color indexes may be marked as transparent", so the maximum possible number of levels is 256, synchronous with the maximum number of color indexes in an 8-bit indexed image.

[Jongware]

https://forums.adobe.com/people/Steve+Werner  wrote

Try resaving the PNG in Photoshop. Some applications seem to create non-standard PNG files.

In this case it's InDesign which does not support some PNG formats, even though they are standard. 8-bit indexed color with a transparency channel is one of these.

[Dave Creamer of IDEAS]

Is the rest of the layout "grayed" out? If yes, check your Flattener Preview panel.