Legacy ImageMagick Discussions Archive

[EDIT: I had a "-set" present that shouldn't have been.] P.S. -- I suppose one could simulate a consistent "working colorspace" e.g. by inserting $c or %c% after every operation (including reading in a file), where c is a shell variable defined as '-colorspace sRGB' or '-colorspa...

1. When I'm editing interactively, I'm curious, what IM-based interactive editing software are you using? I chop and change the image between colorspaces as the need arises, but the main edit window shows a sRGB version of the image. So the knobs and sliders are labelled L,a,b or L,u,v or whatever,...

Ideally, I'd like IM to be colorspace-neutral. It should work equally well in any colorspace: sRGB, linear, AdobeRGB, YUV or whatever. But it doesn't. In my own work, I often... -colorspace {whatever} -set colorspace sRGB ...then continue working with the three or four channels, knowing that IM won...

By request, I'm submitting this simple issue in reading linear png files, separately from another thread (where we were mostly discussing the wisdom of writing linear png files to begin with under certain circumstances). The problem is that on reading a linear png, i.e. a png file with a GAMA=1 chun...

Snigbo, thanks for your thoughtful analysis. This would be IM saying, "I could do what you have asked for, save linear as PNG, but that's unwise so I'll do something else instead." A user hasn't necessarily "asked for" linear output at all. In fact many people may be unaware that...

Fred, going from linear float to linear integer (linear png) is may sound "logical" but linear floating point is a *good* way to store image data and linear integer is *not* such a good way in that it is inefficient and entails more loss of perceptually-relevant data than nonlinear integer...

There's no harm in writing 16-bit sRGB PNG images. Right, so why can't it be the default, even if we happen to currently be working in a linear colorspace (perhaps because we read in an hdri image)? Just because we're working on it as a linear float image does not mean it would be desirable to stor...

we recommend using 8-bit sRGB rather than 16-bit linear samples for export for web use Sure, but if I want to use 16-bit (or if IM is defaulting to 16-bit and I haven't given it any thought), there is certainly no harm in using 16-bit sRGB vs 16-bit linear. If it happens to be read directly by a br...

glennrp wrote: ↑2017-07-28T16:08:43-07:00 ... And they recommend exporting images as 8-bit sRGB for use by the world, ...

Okay, so, at least if we're writing an 8-bit per sample PNG file would you agree that sRGB should be the default, rather than whatever-colorspace-the-image-just-so-happens-to-already-be-in-for-whatever-reasons?

Most software can handle 16-bit png just fine, so long as it's sRGB: [edit] even ordinary web browsers like chrome, firefox, IE, and opera. The PNG developers are perhaps pointing out that if you insist on using a linear colorspace with an integer format, you better not use 8 bits -- 16 bits is much...

But IM seems to be decoding it (as linear) and converting it to sRGB in coders/hdr.c, but then setting image->gamma=1.0 which means it is still linear. Nope... on reading the HDR file it looks to me like it correctly sets the colorspace to linear RGB (not sRGB) initially, in 7.0.6-2 Q16 HDRI at lea...

Glenn, it looks to me like the image data is correctly getting transformed from sRGB to linear RGB in order to write it to HDR, as HDR is a linear-only format. The sG(i.e. G in sRGB)=128/255=50.2% in sRGB is transformed to linearG(i.e. G in RGB)=21.09% in RGB and this value is written to one.hdr and...

Okay, let's split the solution into three parts, from most important (uncontroversial?) to least: 1) At a bare minimum, when IMv7 reads in a png file having gamma=1, it should consider this to be in RGB (linear) colorspace, not sRGB as it (at least IM 7.0.6-2 Q16 HDRI) does today. How can it make se...

Png standard defines a gamma chunk but this is a poor and incomplete substitute for specifying a colorspace (like tiff's photometric interpretation) and is generally ignored. I've never seen an image viewer etc that actually uses this gama and modifies the data accordingly when displaying it or writ...

Does anyone agree or disagree that we should consider *not* writing "linear png" files anymore by default (i.e. instead we should convert to sRGB upon writing to them, just as when writing jpeg or other sRGB file formats), to avoid the problems associated with having png files that have li...