overlayed transparency different results

[ivbera 13]

Hello

I am working with pdfs and want to have a transparent colored object above it.

The pdf are mostly transparent but have some white areas in it.
The colored object is displayed differently on white planes or on transparent areas.
The results also varie depending on how I placed it.

I expect all white colored areas to be the same color in the blue rectangle.

picture frame and transparancy.afpub

[dominik 504]

9 minutes ago, ivbera said:

Hello

I am working with pdfs and want to have a transparent colored object above it.

The pdf are mostly transparent but have some white areas in it.
The colored object is displayed differently on white planes or on transparent areas.
The results also varie depending on how I placed it.

I expect all white colored areas to be the same color in the blue rectangle.

picture frame and transparancy.afpub

Hello @ivbera,

for some reason the picture frame in example #3 has a white fill. If you remove the fill it looks the same as #1 & #2.

I assume the PNG in #4 will look the same if you create/export it with a transparent background.

Would this work for you?
d.

[ivbera 13]

1 hour ago, dominik said:

Would this work for you?

Not really. I work with pdfs for vector reasons.

1 and 2 are also not the result i want. some areas are darker than the others, but effectively it is white and it should be the same.

I think this is a problem to be fixed and not to be work around.

[dominik 504]

24 minutes ago, ivbera said:

1 and 2 are also not the result i want.

Oh, then I misunderstood your question. Sorry for that.

Hope to see that get fixed.
d.

[Pauls 176]

I wonder if the png image is a colour conversion issue - do you have the original png

[Lagarto 47]

On 6/23/2019 at 5:27 PM, dominik said:

I expect all white colored areas to be the same color in the blue rectangle.

If you have a transparent colored area on top of a white object, it looks different than than on a transparent object, unless the "paper" (background) of a document is calculated as white.

When you create a PDF file, the document background is by default shown as white, unless specifically ignored (considered as transparent), so you get results that you want in most situations. If you use the option to flatten the pdf, Publisher will rasterize the document, but when it does, it does not flatten the objects with "white" background (but leaves the background transparent, if it is transparent in the original images), which results in colored transparency looking different on white than on transparent background (unless the viewer software adds the background). Whether the background of the resulting pdf is shown as uniformly white depends on the pdf viewer and the way it renders the image.

To avoid the problem, you should export the pdf using some other option than (flatten). You could also add a white rectangle behind all objects to guarantee that you have uniform white background behind all objects. That would let you avoid dependency on viewers and ensure that the background looks the same whether you have transparent or white background in your source images.

[dominik 504]

3 hours ago, Lagarto said:

To avoid the problem, you should export the pdf using some other option than (flatten). You could also add a white rectangle behind all objects to guarantee that you have uniform white background behind all objects. That would let you avoid dependency on viewers and ensure that the background looks the same whether you have transparent or white background in your source images.

That is an interesting advice. I‘ll take that into account for the next time. Thanks.

d.

[ivbera 13]

@Lagarto You are right. But I still think it is weird for it to display this way and export different.

 

On 7/16/2019 at 5:34 PM, Pauls said:

do you have the original png

Sorry, I was away on a long trip...
It is not a png, but an pdf, I have it attached.

 

7_stadtarchiv_biel_a3.pdf

[Pauls 176]

if you place the image into an RGB colour format file do you get the result you expect ?

[Lagarto 47]

I do not think that this is a bug. As mentioned above, the effect of transparency is calculated against underlying colors. White background results in different effect than transparent background. See attached an edited document where white rectangle is placed behind all objects, and the PDF exported from the document. The background (and accordingly the outlook of the blue transparent object) is now uniform.

picture frame and transparancy_whiterectangle.afpub

picture frame and transparancy_whiterectangle.pdf

[Lagarto 47]

 

On 9/3/2019 at 11:17 AM, ivbera said:

@Lagarto You are right. But I still think it is weird for it to display this way and export different.

 

The difference is explained by the fact that the part of the blue transparency that was originally on the white background, has already been "flattened" (that is, its effect is calculated and resolved, and it is now just a shade of blue), while the part that is on transparent background is still an RGB blue with "A" transparency percentage. The shade of blue that it will turn to, depends on the renderer application and the color of the background at the time the image is rendered, and even if it is flattened against white background, the blue may look different due to the differences in color space (e.g., the original effect of transparent blue against white was perhaps resolved using the Adobe RGB color space, while the browser that resolves the remaining of the transparencies is likely to render the image in sRGB color space).

[Lagarto 47]

To illustrate the role of color space, here is how the unflattened image, which was exported in CMYK color space, is shown if you force sRGB color space on it in Adobe Acrobat (the reddish blue parts have already been flattened against the white background while the purer blue has still a transparency value, so it gets its final blue tone in the renderer application that resolves the remaining transparencies). This simulates how the browser would show the source image's transparency cmyk blue against white in sRGB color space.

 

But when you view the pdf in intended color space (CMYK), the blues get identical tones:

 

[ivbera 13]

Thank you for the explanation. I can work with this.

[Lagarto 47]

You're welcome. A white (CMYK 0, 0, 0, 0) rectangle on a master page would probably do the job without causing problems on pages where it is not needed.

I am not sure how Affinity apps actually handle transparencies, but in the example job which was in CMYK color space (possibly because of color profile conversion done when I opened the file), I used CMYK white and the resulting pdf shows consistent background (already in Publisher immediately after the rectangle has been added).

In InDesign it is possible to specifically define the Transparency Blend Space and typically it is the same as the document's main target color space, but I guess it has been made a choice because the one that is more useable may depend on complexity of the transparency effect and what else you have on the document that is affected by the transparency and in which color space (and also because the document often has more than one PDF export targets, so the blend space can be changed as needed). But the point is that it is good to have the background in the same application that creates the effect so that everying can be resolved in one go and nothing is left for an external renderer.